The achievements of the e+e- Factories have been impressive. The KEK B- Factory has achieved a peak luminosity of 1.7x1034 cm2/s and the PEP-II B-Factory has reached 1.2x1034 cm2/s while the Dafne Phi-Factory has obtained 1.5x1032 cm2/s. Early in the B-Factory running, CP violation in the B meson system was found to be consistent with the prediction of the Standard Model. Now all three factories are integrating as much luminosity as they can in order to look for rare decay channels that may have a rate that differs from the value predicted by the Standard Model and therefore hint at New Physics. I will give a status report on the most recent accomplishments of all three factories PEP-II, KEKB and Dafne and will show what the three facilities have for plans to further improve performance.
CLASSE, Ithaca
University of Minnesota, Minneapolis, Minnesota
CESR-LEPP, Ithaca, New York
Cornell University, Department of Physics, Ithaca, New York
Technion, Haifa
In April 2008, we propose to begin operation of the Cornell Electron Storage Ring (CESR) as a test accelerator, CesrTA, for International Linear Collider (ILC) damping ring research. Utilizing 12 damping wigglers, the baseline CesrTA lattice at 2.0 GeV will offer a natural geometric emittance of 2.25 nm. An experimental program has been laid out which focuses on several key areas of damping rings R&D. First we will test vacuum chamber designs to suppress electron cloud growth in the wiggler magnets. Secondly, we will develop correction, tuning and emittance monitoring strategies to achieve vertical emittances of a few picometers. As part of this effort we will validate alignment and survey techniques being developed by the Linear Collider Alignment and Survey group (LiCAS) for curved tunnel applications. After achieving ultra-low emittance, we intend to explore the impact of the electron cloud, the fast ion instability and other beam dynamics effects on ultra-low emittance beams. Finally, we plan to test various technical systems required for the ILC damping rings. This paper provides an update on conceptual design issues for CesrTA and describes the experimental program in detail.
CESR-c operates with twelve 2.1 Tesla wigglers that account for 90% of the synchrotron radiation with beam energy in the range of 1.8 to 2.1 GeV. The wigglers reduce the radiation damping time from 0.5 seconds to 50 milliseconds. The carefully designed wigglers restrict neither physical nor dynamic aperture of the storage ring, though both quadrupole and sextupole distributions must be tailored to compensate the primary optics effects of the wigglers. Colliding beam performance limits are determined by the numerous parasitic beam-beam interactions in the single ring. Several approaches taken to mitigate these limiting effects are described herein. The CESR-c wigglers are an excellent match to the requirements for future damping rings. We describe how with flexible optics, extensive infrastructure, and resource expertise, they form an effective test bed for assessment and solution of damping ring issues such as electron cloud and ion effects, and achieving ultra-low emittance beams.
IHEP Beijing, Beijing
Jefferson Lab, Newport News, Virginia
CEBAF is a 5-pass, recirculating cw electron linac operating at ~6 GeV. The 12-GeV Upgrade is a $300M project anticipated to receive Critical Decision 2 approval in late summer of 2007 and begin construction activities in 2008; funding for the project is provided by the DOE Office of Nuclear Physics which will double the beam energy. The new energy reach will permit significant extensions in research into non-perturbative aspects of QCD. Areas of interest are Generalized Parton Distributions (GPDs), measurements at high-xBjorken, and the use of hybrid mesons to explore the nature of quark confinement. The upgrade includes: doubling the accelerating voltages of the linacs by adding 10 new high-performance cryomodules plus the requisite expansion of the 2K cryogenics plant and rf power systems, upgrading the beam transport system from 6 GeV to 12 GeV capability through extensive re-use of existing hardware, adding one recirculation arc, adding a new experimental area and the beamline to it, building new experimental equipment for the GPD, high-xBjorken, and hybrid mesons programs. The presentation will touch on the science and give some details of the accelerator plans.
BINP SB RAS, Novosibirsk
* A. A. Zholentz et al., Phys. Lett. B 96 (1980) 214-216.** T. A. Armstrong et al., Phys. Rev. D47 (1993) 772-783.
Subpicosecond x-ray pulses are now routinely obtained at the ALS, BESSY and SLS light sources using laser e-beam slicing technique. Other x-ray pulse shortening techniques were also proposed and are now under consideration for ALS, APS, DIAMOND and PETRA light sources. In this talk I review current results and discuss R&D plans and activity.
INFN/LNF, Frascati (Roma)
INFN-Milano, Milano
INFN-Roma II, Roma
UCLA, Los Angeles, California
ENEA C. R. Frascati, Frascati (Roma)
INFN-Roma, Roma
Jefferson Lab, Newport News, Virginia
Operation of the JLab IR Upgrade FEL at CW powers in excess of 10 kW requires sustained production of high electron beam powers by the driver ERL. This in turn demands attention to numerous issues and effects, including: cathode lifetime; control of beamline and RF system vacuum during high current operation; longitudinal space charge; longitudinal and transverse matching of irregular/large volume phase space distributions; halo management; management of remnant dispersive effects; resistive wall, wake-field, and RF heating of beam vacuum chambers; the beam break up instability; the impact of coherent synchrotron radiation (both on beam quality and the performance of laser optics); magnetic component stability and reproducibility; and RF stability and reproducibility. We discuss our experience with these issues and describe the modus vivendi that has evolved during prolonged high current, high power beam and laser operation.
NSRRC, Hsinchu
IUCF, Bloomington, Indiana
Vanderbilt University, Nashville, Tennessee
DESY, Hamburg
CLASSE, Ithaca
CHESS, Ithaca, New York
Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
Cornell University, Department of Physics, Ithaca, New York
The status of plans for an Energy-Recovery Linac (ERL) X-ray facility at Cornell University is described. Currently, Cornell operates the Cornell High Energy Synchrotron Source (CHESS) at the CESR ring and the ERL is planned to be an extension to the CESR ring with the addition of a 5-GeV superconducting c.w. linac. Topics covered in this paper include the full layout on the Cornell campus, the different operation modes of the accelerator, methods to limit emittance growth, control of beam-ion effects and ways to limit transverse instabilities. As an upgrade of the CESR ring, special attention is given to reuse of many of the existing components. The very small electron-beam emittances would produce an x-ray source that is highly superior than any existing storage-ring light source. The ERL includes 18 X-ray beamlines optimized for specific areas of research that are currently being defined by an international group of scientists. This planned upgrade illustrates how other existing storage rings could be upgraded to work as ERL light sources with vastly improved beam qualities and with limited dark time for x-ray users.
AIST, Tsukuba, Ibaraki
SHI, Tokyo
LANL, Los Alamos, New Mexico
For national security, it is important to detect the presence of Special Nuclear Materials (SNM), especially Highly-Enriched Uranium (HEU). Generally used methods for such detection include interrogation by photons and neutrons. For example, photofission in HEU can be initiated with 14-MeV photons. The resulting delayed neutrons and photons from the fission fragments are clear signatures of the presence of HEU. One can generate high-energy photons using electron accelerators via various mechanisms. In this paper, we will describe two of them, namely electron bremsstrahlung and Compton-backscattered photons. We focus on these two mechanisms because they cover a wide range of accelerator requirements. Electron bremsstrahlung can be generated using a compact low-energy electron linac while the generation of Compton-backscattered photons requires a high-energy electron accelerator of a few hundred MeV. We review these two options, describe their accelerator requirements, and compare their relative merits.
LLNL, Livermore, California
PPPL, Princeton, New Jersey
LBNL, Berkeley, California
University of electro-communications, Tokyo
We describe near term heavy-ion beam-driven warm dense matter (WDM) experiments. Initial experiments are at low beam velocity, below the Bragg peak, increasing toward the Bragg peak in subsequent versions of the accelerator. The WDM conditions are envisioned to be achieved by combined longitudinal and transverse neutralized drift compression to provide a hot spot on the target with a beam spot size of about 1 mm, and pulse length about 1-2 ns. The range of the beams in solid matter targets is about 1 micron, which can be lengthened by using porous targets at reduced density. Initial candidate experiments include an experiment to study transient darkening in the WDM regime; and a thin target dE/dx experiment to study beam energy and charge state distribution in a heated target. Further experiments will explore target temperature and other properties such as electrical conductivity to investigate phase transitions and the critical point.
LNLS, Campinas
Institute of High Current Electronics, Tomsk
GSI, Darmstadt
TEMF, Darmstadt
The Wien filter is well known as a common energy analyzer and is also used more and more as a compact variant of a spin rotator at low energy for electrons. The Wien filter based on a homogenous magnetic and electric field that are perpendicular to each other and transverse to the direction of the electrons. The rotation of the spin vector is caused by the magnetic field. If the force equilibrium condition is fulfilled the beam should not be deflected at the Wien filter. Simulations show that in the fringe fields the electrons get a kick. Therefore full 3D simulations of the electromagnetic fields and beam dynamics simulations are studied in detail at the example of the Wien filter at the new polarized 100 keV electron injector at the S-DALINAC. The results of the simulations with CST Design Environment(TM), MAFIA and V-Code are presented.
DESY, Hamburg
The next generation of FEL's (Free Electron Lasers) require a long and short term stable synchronisation of RF reference signals with an accuracy of 10 fs. For that an optical synchronisation system is developed for FLASH at DESY, that is based on optical pulse train which carry the timing information encoded in its precise repetition rate. The optical pulse train has to be converted into an RF signal to provide a local reference for calibration and operation of RF based devices. The drift and jitter performance of the optical to RF converter influences directly the phase stability of the accelerator. Three different methods for optical to RF converters, namely the direct photodiode detection, injection locking and a sagnac loop interferometer are currently under investigation. In this paper we concentrate on the jitter and drift performance of the direct photodiode conversion and show its limitations from measurement results.
Warsaw University of Technology, Institute of Electronic Systems, Warsaw
DESY, Hamburg
ELETTRA, Basovizza, Trieste
SAES Getters S.p. A., Lainate
Kyoto IAE, Kyoto
USTC/NSRL, Hefei, Anhui
KAERI, Daejon
20MeV proton linear accelerator of the PEFP(Proton Engineering Frontier Project) has above 10 magnet power supplies and getter pumps to interface with Modbus protocol. VME IOC(Input Output Controller) has been designed and constructed for the control system by using VME serial I/O. The driver support module of the VME IOC has been developed to initialize the IO board and communicate with the instruments through EPICS. Operating console and storage module for operators in the control room has been programmed on PC and SUN of the operator interface.
PAL, Pohang, Kyungbuk
NSRRC, Hsinchu
JAI, Oxford
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
SLAC, Menlo Park, California
Royal Holloway, University of London, Surrey
Electro-optic techniques might allow implementing a laserwire scanner for intra-train scanning at the ILC with scanning speed in excess of 100 kHz. A scanner capable of running at such a rate would in fact provide information about the particle beam size in about one hundred different positions along the bunch train (approximately 1ms long for the ILC*). The design of an electro-optic deflector capable to scan within 10-100 microsecond is presented, discussed and analytically treated.
* ILC Baseline Conceptual Design (2006).: http://www.linearcollider.org/.
Fermilab, Batavia, Illinois
The current Fermilab A0 Photoinjector laser system includes a seed laser, a flashlamp pumped multipass amplifier cavity, a flashlamp pumped 2-pass amplifier system followed by an IR to UV conversion stage. However the current system can only deliver up to 800 pulses due to the low efficiency of Nd:Glass used inside multi-pass cavity. In this paper we will report the effort to develop a new multi pass cavity based on Nd:YLF crystal end-pumped by diode laser. We will also discuss the foreseen design of the laser system for the NML accelerator test facility at Fermilab.
UMD, College Park, Maryland
Beam based alignment and control has been a critical issue for many accelerators. In this paper, we've developed a new approach that can correct the beam orbit using a systematic quad-scan method, where there is an insufficient number of beam position monitors. In this approach, we've proposed a calibrated response matrix. This matrix takes consideration of the different sensitivities of different quadrupoles in the lattice. With the calibrated response matrix, we can greatly enhance our ability to control the beam centroid motion and reduce the control effort.
FEL/Duke University, Durham, North Carolina
PAL, Pohang, Kyungbuk
Dimtel, Redwood City, California
Cornell University, Department of Physics, Ithaca, New York
Cornell University, Ithaca, New York
Cornell University is developing a high brightness, high average current electron source for the injector of an ERL based synchrotron radiation source. The source is a DC electron gun with a negative electron affinity photoemission cathode. The photocathode is illuminated by a 1300 MHz CW train of optical pulses to produce a 100 mA average current beam. The optical pulse train is generated by frequency doubling the output of a diode-pumped, mode-locked Yb-fiber oscillator-amplifier system. The 50 MHz fundamental frequency oscillator is locked on its 26th harmonic to produce the 1300 MHz train. The oscillator output is amplified in three stages and doubled to give 26 W in the green. The doubled beam is diffraction limited (M2 = 1.08) with a pulse width of 2.5 ps. This pulse is split and differentially delayed in a series of birefringent crystals to produce a flat top temporal profile with fast rise and fall times. The final pulse shape is measured by cross-correlation. The pulses are spatially shaped by a commercial aspheric lens system. A full power system operating at 50 MHz is in routine use for electron beam measurements. Detailed laser performance information will be presented.
LLNL, Livermore, California
The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has been specifically designed for advanced rf gun applications, with a special emphasis on the production of high-brightness electron beams for free-electron lasers and Compton scattering light sources. The laser pulse can be shaped to a flat-top in both space and time with a duration of 10 ps FWHM and rise and fall times under 1 ps. The pulse energy is 100 micro-joules at 261.75 nm and the spot size diameter of the beam at the photocathode measures 2 mm. A fiber oscillator and amplifier system generates a chirped pump pulse at 1047 nm; stretching is achieved in a chirped fiber Bragg grating. A single multi-layer dielectric grating based compressor recompresses the input pulse to 250 fs FWHM and a two stage harmonic converter frequency quadruples the beam. A custom-designed diffractive optic reshapes the input pulse to a flat-top. Temporal shaping is achieved with a Michelson-based ultrafast pulse stacking device with nearly 100% throughput. The integration of the system, as well as preliminary electron beam measurements will be discussed.
ORNL, Oak Ridge, Tennessee
LBNL, Berkeley, California
IUCF, Bloomington, Indiana
LANL, Los Alamos, New Mexico
SLAC, Menlo Park, California
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos National Laboratory Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). Evidence obtained from these tests suggests that further improvement in performance is limited by beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback. Here we describe the present system configuration, system optimization, results of several recent experimental tests, and results from studies of factors limiting its performance.
Omega-P, Inc., New Haven, Connecticut
Euclid TechLabs, LLC, Solon, Ohio
KEK, Ibaraki
Ceramics Ltd., St. Petersburg
A fast, electrically-controlled phase shifter is described with parameters suitable for operation with the SC acceleration structure of the electron cooling system of Relativistic Heavy Ion Collider (RHIC) at BNL. The phase shifter is a key element of the external RF vector modulator that is capable of fast tuning of the cavities against microphonics, Lorentz force and beam instabilities in a way that can possibly lead to an order of magnitude reduction in the required RF power. The phase shifter is based on a shortened low-impendence coaxial line with ferroelectric rings. The dielectric constant of the ferroelectric rings is altered by applying a 4.2 kV voltage that provides an RF phase shift from 0 to 180 deg.
The College of William and Mary, Williamsburg
Jefferson Lab, Newport News, Virginia
Two styles of Panofsky Quadrupoles with integral corrector dipole windings are in use in the electron beam line of the Free Electron Laser at Jefferson Lab. We combined the functions into single magnets, adding hundreds of Gauss-cm dipole corrector capability to existing quadrupoles because space is at a premium along the beam line. Superposing high quality dipole corrector field on a high quality, weak (600 to 1'000 Gauss) quadrupole is possible because the parallel slab iron yoke of the Panofsky Quadrupole acts as a window frame style dipole yoke. The dipole field is formed when two current sources, designed and made at Jlab, add and subtract current from the two opposite quadrupole current sheet windings parallel to the dipole field direction. The current sources also drive auxiliary coils at the yoke's inner corners that improve the dipole field. Magnet measurements yielded the control system field maps that characterize the two types of fields. Details of field analysis using OPERA, construction methods, wiring details, magnet measurements and the current sources are presented.
Jefferson Lab, Newport News, Virginia
Recent upgrades to the CEBAF Polarized Source include a fiber-based seed laser, capable of producing pulses with frequency centered at 499 MHz. Combined with the existing three-beam Chopper, an aliasing, or beat frequency technique is used to produce long time intervals between individual electron microbunches (tens of nanoseconds) by merely varying the nominal 499 MHz drive laser frequency by <20%. This RF Laser modulator uses a divider and heterodyne scheme to maintain coherence with the accelerator Master Oscillator, while providing delay resolution in increments of 2ns. Laser repetition frequencies producing bunch repetition rates between 20 MHz and 100 MHz are demonstrated, resulting in time delays between 50 and 10 ns, respectively. Also, possible uses for such a beam are discussed as well as intended development. Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177
LANL, Los Alamos, New Mexico
University of Tennessee, Knoxville, Tennessee
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
ORNL, Oak Ridge, Tennessee
KEK, Ibaraki
Diamond stripping foils are under development for the SNS. Free-standing, flat 350 microgram/cm2 foils as large as 17 x 25 mm have been prepared. These nano-textured polycrystalline foils are grown by microwave plasma-assisted chemical vapor deposition in a corrugated format to maintain their flatness. They are mechanically supported on a single edge by a residual portion of their silicon growth substrate; typical fine foil supporting wires are not required for diamond foils. Six foils were mounted on the SNS foil changer in early 2006 and have performed well in commissioning experiments at reduced operating power. A diamond foil was used during a recent experiment where 12 microCoulombs of protons, approximately 40% of the design value, were stored in the ring. A few diamond foils have been tested at LANSCE/PSR, where one foil was in service for a period of five months (820 Coulombs of integrated injected charge) before it was replaced. Diamond foils have also been tested in Japan at KEK (650 keV H-) where their lifetimes slightly surpassed those of evaporated carbon foils, but fell short of those for Sugai's new hybrid boron carbon (HBC) foils.
BNL, Upton, Long Island, New York
In this paper we describe unique features of magnets for R&D ERL, which is under construction in Collider-Accelerator Department, BNL. The R&D ERL serves as a test-bed future BNL ERLs, such as electron-cooler-ERL for RHIC and 20 GeV ERL for future electron-hadron, eRHIC. We present selected designs of various dipole and quadrupole magnets, which are used in Z-bend merging systems and the returning loop, 3-D simulations of the fields in these magnets, particle tracking and analysis of magnet's influence on the beam parameters. We discuss an uncommon method of setting requirements on the quality of magnetic field and transferring them into measurable parameters as well as into manufacturing tolerances. We compare selected simulation with results magnetic measurements.
The Relativistic Heavy Ion Collider (RHIC) is designed to provide luminosity over a wide range of beam energies and species, including heavy ions, polarized protons, and asymmetric beam collisions. In the first seven years of operation there has been a rapid increase in the achieved peak and average luminosity, substantially exceeding design values. Work is presently underway to achieve the Enhanced Design parameters in about 2008. Planned major upgrades include the Electron Beam Ion Source (EBIS), the RHIC-II electron cooling upgrade, and construction of an electron-ion collider (eRHIC). We review the expected RHIC upgrade performance. Electron cooling and its impact on the luminosity at various collision energies both for heavy ions and protons are discussed in detail.
Fermilab, Batavia, Illinois
LANL, Los Alamos, New Mexico
LBNL, Berkeley, California
LLNL, Livermore, California
UCB, Berkeley, California
Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 us duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.*
* M. Kireeff Covo, A. W. Molvik, A. Friedman, J.-L. Vay, P. A. Seidl, G. Logan, D. Baca, and J. L. Vujic, Phys. Rev. Lett. 97, 054801 (2006).
BNL, Upton, Long Island, New York
ALBA, Bellaterra (Cerdanyola del Valles)
Since 2001 RHIC has experienced electron cloud effects, which have limited the beam intensity. These include dynamic pressure rises – including pressure instabilities, a reduction of the stability threshold for bunches crossing the transition energy, and possibly slow emittance growth. We report on the main observations in operation and dedicated experiments, as well as the effect of various countermeasures including baking, NEG coated warm pipes, pre-pumped cold pipes, bunch patterns, scrubbing, and anti-grazing rings.
LBNL, Berkeley, California
LLNL, Livermore, California
Tech-X, Boulder, Colorado
We present recent advances in the modeling of beam-electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation.
Tech-X, Boulder, Colorado
* C. Nieter, J. R. Cary, J. Comp. Phys. 196 (2004) 448.** S. Dey, R. Mittra, IEEE Microwave and Guided Wave Letters 7 (1997) 273.
PSI, Villigen
LBNL, Berkeley, California
UCLA, Los Angeles, California
SLAC, Menlo Park, California
BNL, Upton, Long Island, New York
Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60 MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12 MeV. The Trafic4 simulation confirms the observation.
The paper was published at PRST-AB, November 2006
SLAC, Menlo Park, California
DESY, Hamburg
LBNL, Berkeley, California
The Linac Coherent Light Source (LCLS) is a SASE x-ray free-electron laser project presently under construction at SLAC. The injector section from RF photocathode gun through the first bunch compressor chicane was installed during the Fall of 2006. The first bunch compressor chicane is located at 250 MeV and nominally compresses a 1-nC electron bunch from an rms length of about 1 mm to 0.2 mm. The degree of compression is highly adjustable using RF phasing and also chicane magnetic field variations. Transverse phase space and bunch length diagnostics are located immediately after the chicane. We present measurements and simulations of the longitudinal and transverse phase space after the chicane in various beam conditions, including extreme compression where coherent radiation effects are expected to be striking.
UMD, College Park, Maryland
Circular accelerators and storage rings have traditionally been designed with limited intensity in order to avoid resonances and instabilities. The possibility of operating a ring beyond the Laslett tune shift limit has been suggested but little tested, apart from a pioneering experiment by Maschke at the BNL AGS in the early 1980s. We have recently circulated the highest-space-charge beam in a ring to date in the University of Maryland Electron Ring (UMER), achieving a breakthrough both in the number of turns and in the amount of current propagated. At undepressed tunes of up to 7.6, the space charge in UMER is sufficient to depress the tune by nearly a factor of 2, resulting in tune shifts up to 3.6. This makes the UMER beam the most intense beam that has been propagated to date in a circular lattice. This is an exciting and promising result for future circular accelerators, and the UMER beam can now be used as a platform to study intense space charge dynamics in rings.
KEK, Ibaraki
[1] T. Ieiri et al., Proc. of EPAC06, Edinburgh, Scotland, 2101 (2006).
LANL, Los Alamos, New Mexico
TechSource, Santa Fe, New Mexico
SLAC, Menlo Park, California
Recent beam physics studies on the two-stream e-p instability at LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Experimental results will be presented on various characteristics of electron cloud obtain from experiments using this diagnostic and compared with simulations. Results include data on flux and energy spectra of electrons striking the vacuum chamber, the line density and lifetime of electrons trapped in the quadrupole after the beam has been extracted as well as evidence regarding electrons ejected from the magnet during passage of the proton beam.
LANL, Los Alamos, New Mexico
LBNL, Berkeley, California
LLNL, Livermore, California
LLNL, Livermore, California
University of Missouri - Rolla, Rolla, Missouri
University of Missouri, Columbia, Columbia, Missouri
TPL, Albuquerque, NM
Progress in the development of compact induction accelerators employing advanced vacuum insulators and dielectrics will be described. These machines will have average accelerating gradients at least an order of magnitude higher than existing machines and can be used for a variety of applications including flash x-ray radiography and medical treatments. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described.
DULY Research Inc., Rancho Palos Verdes, California
High-gradient electron guns can suppress space-charge induced transverse emittance growth when the electron beam is still in the low-energy injection stage. A synchronizable, high-voltage pulser can be used to power up a high-gradient gun. We propose to build a 200 kV pulser using a special trigger that utilizes a laser-photocathode sub-system. A laser trigger beam will first energize a spark gap, and then provide a second trigger signal from a photocathode using its leftover energy, to further close the gap. This system will not only raise the utilization efficiency of the laser beam energy, but also enhance the reliability of the trigger circuit. Our preliminary analysis shows that the proposed system will significantly improve the performance of the laser trigger pulse with the jitter on the order of hundreds of picoseconds. It is expected that the pulser can be used in the applications of high gradient guns as well as in other devices that need high precision trigger such as short pulse lasers, streak cameras, impulse radiating antennas, etc.
Stangenes Industries, Palo Alto, California
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
Fermilab, Batavia, Illinois
UNM, Albuquerque, New Mexico
LBNL, Berkeley, California
SLAC, Menlo Park, California
We discuss our progress on integration of the coupled Vlasov-Maxwell equations in 4D. We emphasize Coherent Synchrotron Radiation from particle bunches moving on arbitrary curved planar orbits, with shielding from the vacuum chamber, but also include space charge forces. Our approach provides simulations with lower numerical noise than the macroparticle method, and will allow the study of emittance degradation and microbunching in bunch compressors. The 4D phase space density (PSD) is calculated in the beam frame with the method of local characteristics (PF). The excited fields are computed in the lab frame from a new double integral formula. Central issues are a fast evaluation of the fields and a deep understanding of the support of the 4D PSD. As intermediate steps, we have (1) developed a parallel self-consistent code using particles, where an important issue is the support of the charge density*; (2) studied carefully a 2D phase space Vlasov analogue; and (3) derived an improved expression of the field of a 1D charge/current distribution which accounts for the interference of different bends and other effects usually neglected**. Results for bunch compressors are presented.
* Self Consistent Particle Method to Study CSR Effects in Bunch Compressors, Bassi, et.al., this conference.** CSR from a 1-D Bunch on an Arbitrary Planar Orbit, Warnock, this conference.
ASP, Clayton, Victoria
Danfysik A/S, Jyllinge
* http://www.danfysik.com/
ACCEL, Bergisch Gladbach
BESSY GmbH, Berlin
GSI, Darmstadt
JLAB, Newport News, Virginia
BESSY is proposing a demonstration facility, called STARS, for a two-stage high-gain harmonic generation free electron laser (HGHG FEL). STARS is planned for lasing in the wavelength range 40 to 70 nm, requiring a beam energy of 325 MeV. The facility consists of a normal conducting gun, three superconducting TESLA-type acceleration modules modified for CW operation, a single stage bunch compressor and finally a two-stage HGHG cascaded FEL. This paper describes the faciliy layout and the rationale behind the operation parameters.
BESSY GmbH, Berlin
PTB, Berlin
In 2003, the Metrology Light Source (MLS) was approved, a dedicated low energy electron storage ring of the Physikalisch-Technische-Bundesanstalt (PTB), the German national metrology institute. Design, construction and operation of the MLS are realized by BESSY, based on the PTB requirements for a permanent accessible radiometry source, optimized for the spectral range between UV up to VUV. The MLS is tunable in energy between 200 MeV and 600 MeV. Based on the experiences at BESSY, a highly stable and reliable Race Track Microtron for injection was realized by Danfysik. The commissioning of the 100 MeV microtron at the MLS started in December 2006. The concept and construction as well as the main parameters of the microtron are introduced.
BESSY GmbH, Berlin
PTB, Berlin
The Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute, has built an electron storage ring in close cooperation with BESSY for energies between 200 MeV and 600 MeV. This storage ring, named Metrology Light Source (MLS), will mainly be used for radiometry and can be operated as a primary source standard. The spectral range of the MLS is optimized for UV, EUV and also for Terahertz radiation. Commissioning is planed for May 2007. First MLS commissioning results will be reported.
BESSY GmbH, Berlin
Uni HH, Hamburg
Universität Muenster, Physikalisches Institut, Muenster
BESSY GmbH, Berlin
The cascaded High Gain Harmonic Generation (HGHG) scheme proposed for the BESSY-FEL contains an inherent potential for providing jitter free radiation pulses for pump and probe experiments. In an HGHG stage an energy modulation is imprinted to the electron beam by a seeding radiation. A dispersive section converts this energy modulation to a spatial modulation which is optimized for a particular harmonic. The subsequent radiator is optimized for this harmonics and generates radiation with high power which is used as seeding radiation for the next stage. After passage through the modulator, the seeding radiation become redundant and can be separated from the prebunched electrons using a deflecting dispersive chicane. This radiation and the final FEL output will have a fixed temporal separation as the first one is the driving seeding radiation for the second one. Using the planned test facility for HGHG scheme at BESSY as an example, we present simulation studies for a sequences of two jitter free pump and probe pulses including the deflecting chicane and a suitable beam line.
DESY, Hamburg
INFN/LNF, Frascati (Roma)
DESY, Hamburg
Jefferson Lab, Newport News, Virginia
SLAC, Menlo Park, California
SBUNSL, Stony Brook, New York
BNL, Upton, Long Island, New York
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
UU/ISV, Uppsala
Uni HH, Hamburg
FYSIKUM, AlbaNova, Stockholm University, Stockholm
BESSY GmbH, Berlin
DESY, Hamburg
* E. Saldin, E. Schneidmiller, M. Yurkov, NIM A 539 (2005), 499
University of Karlsruhe, Karlsruhe
FZK, Karlsruhe
University of Erlangen-Nurnberg, Physikalisches Institut II, Erlangen
CERN, Geneva
DESY Zeuthen, Zeuthen
INRNE, Sofia
YerPhI, Yerevan
INFN/LASA, Segrate (MI)
BESSY GmbH, Berlin
Uni HH, Hamburg
Beginning 2007, a new gun cavity will be installed at the photo injector test facility at DESY in Zeuthen (PITZ). It will be conditioned towards gradients as high as 60 MV/m. This gradient is required for the operation of the European XFEL. Results from the conditioning for high peak power and high duty cycle will be reported.
ELETTRA, Basovizza, Trieste
INFN-Milano, Milano
Universita degli Studi di Milano, Milano
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
INFN/LNF, Frascati (Roma)
INFN-Milano, Milano
INFN-Roma, Roma
INFN-Milano, Milano
Universita degli Studi di Milano, Milano
RIKEN Spring-8 Harima, Hyogo
AIST, Tsukuba, Ibaraki
Kyoto IAE, Kyoto
UVSOR, Okazaki
Nagoya University, Nagoya
KEK, Ibaraki
RISE, Tokyo
ISIR, Osaka
AIST, Tsukuba, Ibaraki
RIKEN, Saitama
At Waseda University, we have succeeded in generating soft X-rays based on laser Compton scattering. The energies are within "Water Window" part (250~500eV) where the X-ray absorption coefficient of water is much less than that of constituent elements of living body such as carbon, hydrogen and nitrogen. For this reason, it is expected to apply to a bio-microscope with which we can observe living cells without dehydration. To improve the generation system, we remodeled our collision chamber and adopted 3-pass flash lamp amplifier system. With these modifications, we achieved high S/N ratio. The photon number detected by MCP was 278/pulse, tenfold increase of that in last year. Moreover, we succeeded in generating soft X-rays stably for more than 10 hours. Now we are planning to measure two-dimensional distribution of the X-rays by CCD. In this conference, experimental results and future plans will be reported.
KEK, Ibaraki
Kyoto University, Kyoto
Tsukuba-shi, Ibaraki-ken
RISE, Tokyo
RISE, Tokyo
ISIR, Osaka
AIST, Tsukuba, Ibaraki
SHI, Tokyo
TUB, Beijing
This work was supported by the Chinese National Foundation of Natural Sciences under Contract no. 10645002.
TUB, Beijing
TUB, Beijing
PAL, Pohang, Kyungbuk
There are growing interests in generation, preservation and applications of high brightness electron beam. With the rapid development in the techniques for emittance compensation and laser shaping, we are approaching the limit-the uncorrelated thermal emittance. In this paper, we report the measurements of thermal emittance for Cu and Mg. The measurement is conducted in a field-free region. The energy spectrum and angular distribution of the electrons are measured immediately after its emission and further used to reconstruct the initial phase space and the corresponding thermal emittance. We also show how cathode surface roughness* and laser incidence angle as well as its polarization state** affect the quantum efficiency and thermal emittance.
*X. Z. He, High energy physics and nuclear physics,28(2004)1007.**Dao Xiang,et al, NIM A,562(2006)48.
TUB, Beijing
The ultrashort ultraviolet (UV) laser system and the optical transport line for driving the photocathode RF gun at Accelerator Laboratory of Tsinghua University are introduced in the article. Temporal profile of the UV pulse was measured by non-colinear difference frequency generation (DFG) between the UV pulse itself and the jitter-free residual IR laser pulse after third harmonic generation (THG) process. Experiments to measure the dependence of quantum efficiency (QE) on laser polarization state are also performed. Results show that in our case the ratio of QE between p- and s- polarization is more than 2.6.
NSRRC, Hsinchu
NSRRC, Hsinchu
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
ISP, Novosibirsk
STFC/RAL, Chilton, Didcot, Oxon
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Studies of the electron beam dynamics for the 4GLS design are presented. 4GLS will provide three different electron bunch trains to a variety of user synchrotron sources. The 1 kHz XUV-FEL and 100 mA High Average Current branches share a common 540 MeV linac, whilst the 13 MHz IR-FEL must be well-synchronised to them. An overview of the injector designs, electron transport, and energy recovery is given, including ongoing studies of coherent synchrotron radiation, beam break-up and wakefields. This work is being pursued for the forthcoming Technical Design Report due in 2008.
STFC/DL, Daresbury, Warrington, Cheshire
STFC/DL/SRD, Daresbury, Warrington, Cheshire
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
ANL, Argonne, Illinois
A short x-ray pulse source based on the crab cavity scheme proposed by Zholents* is being developed at the Advanced Photon Source (APS). Photon diagnostics that visualizes the electron bunches with transverse momentum chirp and verifies the performance of the short x-ray pulse is required. We present a design study for the imaging diagnostics inside and outside of the crab cavity zone, utilizing both x-ray and visible synchrotron radiation. Several design options of monochromatic and polychromatic x-ray optics will be explored for their compatibility with the short-pulse source. The diagnostics outside of the crab cavity zone will be used to map out stable operation parameters of the storage ring with crab cavities, and to perform single-bunch single-pass imaging of the chirped bunch, which facilitates the tuning of the crab cavity rf phase and amplitude so the performance of the short pulse source can be optimized while other users around the ring will not be disturbed.
* A. Zholents et al., NIM A 425, 385 (1999).
LBNL, Berkeley, California
LLNL, Livermore, California
Due to copious synchrotron radiation from the beam, electron cloud effects are predicted to be important in the wiggler sections of the ILC positron damping ring. In this area of the ring, the physics is inherently 3D. Moreover, a self-consistent calculation of the physics of the electron cloud/beam system is necessary for examining such phenomena as emittance growth in the beam. We present the first calculations of this system with the self-consistent 3D particle-in-cell code WARP/POSINST. The code includes self-consistent space charge for both species, mesh refinement, and detailed models of primary and secondary electron production. Interaction with electrons is assumed to occur only in the wigglers in this model– the beam is moved using maps between wiggler sections.
LBNL, Berkeley, California
The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, and wavelength; utilization of harmonics to attain shorter wavelengths; and precise synchronization of the x-ray pulse with laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FELs, each producing high average brightness, tunable over the soft x-ray-VUV range, and each with individual performance characteristics determined by the configuration of the FEL SASE, enhanced-SASE (ESASE), seeded, self-seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands. FELs would be tailored to specific experimental needs, including production of ultrafast pulses even into the attosecond domain, and high temporal coherence (i.e. high resolving power) beams.
LBNL, Berkeley, California
By "conditioning" an electron beam, through establishing a correlation between transverse action and energy within the beam, the performance of free electron lasers (FELs) can be dramatically improved. Under certain conditions, the FEL can perform as if the transverse emittances of the beam were substantially lower than the actual values. After a brief review of the benefits of beam conditioning, we present a method to generate this correlation through the use of a plasma channel. The strong transverse focusing produced by a dense plasma (near standard gas density) allows the optimal correlation to be achieved in a reasonable length channel, of order 1 m. This appears to be a convenient and practical method for achieving conditioned beams, especially in comparison with other methods which require either a long beamline or multiple passes through some type of ring.
LBNL, Berkeley, California
SLAC, Menlo Park, California
PSI, Villigen
LBNL, Berkeley, California
Nano-tips with high acceleration gradient around the emission surface have been proposed to generate high brightness beams. However, due to the small size of the tip, the charge density near the tip is very high even for a small number of electrons. The Coulomb scattering near the tip can significantly degrade the beam quality and cause extra emittance growth and energy spread. In the paper, we present a numerical study of these effects using a direct relativistic N-body model. We found that emittance growth and energy spread, due to Coulomb scattering, can be significantly enhanced with respect to mean-field space-charge calculations in different parameter regimes.
Jefferson Lab, Newport News, Virginia
PKU/IHIP, Beijing
A free-electron laser based on a superconducting linac is under construction in Peking University. To increase FEL output power, energy recovery is chosen as one of the most potential and popular ways. The design of a beam transport system for energy recovery is presented, which is suitable for the Peking University construction area. Especially, a chicane structure is chosen to change path length at ±20 degree and M56 in the arc is adjusted for fully bunch compression.
BNL, Upton, Long Island, New York
Quiet start scheme is broadly utilized in Self Amplified Spontaneous Radiation (SASE) FEL simulations, which is proven to be correct and efficient. Nevertheless, due to the existing of energy modulation effect and the dispersion section, the High Gain Harmonic Generation (HGHG) FEL simulation will not be improved by the traditional quiet start method. A new approach is presented to largely decrease the macro-particles per slice that can be implemented in both time-independent and time-dependent simulation, accordingly expedites the HGHG FEL simulation especially high order harmonic cascade case and makes the multi-parameter scanning be possible.
UMD, College Park, Maryland
NRL, Washington, DC
Photocathodes for high power free electron lasers face significant engineering and physics challenges in the quest for efficient, robust, long-lived, prompt laser-switched operation. The most efficient semiconductor photocathodes, notably those responsive to visible wavelengths, suffer from poor lifetime due to surface layer degradation, contamination, and desorption. Using a novel dispenser photocathode design, rejuvenation of cesiated surface layers in situ is investigated for semiconductor coatings building on previous results for cesiated metals. Cesium from a sub-surface reservoir diffuses to the surface through a microscopically porous, sintered tungsten matrix to repair the degraded surface layer. The goal of this research is to engineer and demonstrate efficient, robust, long-lived regenerable photocathodes in support of predictive photocathode modeling efforts and suitable for photoinjection applications.
BINP SB RAS, Novosibirsk
FEL/Duke University, Durham, North Carolina
TUNL, Durham, North Carolina
A booster synchrotron has been built and recently commissioned at Duke University Free Electron Laser Laboratory (DFELL) as part of the High Intensity Gamma-ray Source (HIGS) facility upgrade. HIGS is developed collaboratively by the DFELL and Triangular Universities Nuclear Laboratory (TUNL). The booster will provide top-off injection into the Duke FEL storage ring in the energy range of 0.27 - 1.2 GeV. When operating the Duke storage ring to produce high energy Compton gamma ray beams above 20 MeV, continuous electron beam loss occurs. The lost electrons will be replenished by the booster injector operating in the top-off mode. The compactness of the booster posed a challenge for its development and commissioning. The booster has been successfully commissioned in 2006. This paper reports experience of commissioning and initial operation of the booster.
The Duke Free-Electron Laser Laboratory (DFELL) has recently completed two major accelerator/light source development projects - we successfully commissioned the world's first distributed optical klystron FEL (DOK-1 FEL) and a new 0.27-1.2 GeV booster synchrotron. The DOK-1 FEL has a much improved FEL gain compared with traditional optical klystrons. This allows the DOK-1 FEL to become a versatile light source for UV-VUV operation and as a driver for a high-intensity Compton gamma-source. The top-off booster injector for the Duke storage ring is part of the upgrade project of High Intensity Gamma-ray Source (HIGS), a facility jointly developed by the DFELL and Triangle Universities Nuclear Laboratory (TUNL). The accelerator and light source development has created new opportunities for the accelerator physics research. In this paper, we will report our recent progress in accelerator and light source development as well as the ongoing accelerator physics research programs to meet the new challenges in the areas of beam dynamics and beam instability.
CLASSE, Ithaca
In an energy recovery linac (ERL) where beam-loss has to be minimal, and where beam positions and emittances have to be very stable in time, optic errors and beam instabilities due to ion effects have to be avoided. Here we explain why ion clearing electrodes are the least unattractive way of eliminating ions in an ERL and we present calculations of the remnant ion density and its effect on the beam. We also show a design of the clearing electrodes that should be distributed around the accelerator and illustrate their wake-field properties.
Cornell University, Department of Physics, Ithaca, New York
Cockcroft Institute, Lancaster University, Lancaster
KEK, Ibaraki
Recent computational optimizations have demonstrated that it should be possible to construct electron injectors based on photoemission cathodes in very high voltage DC electron guns in which the beam emittance is dominated by the thermal emittance from the cathode. Negative electron affinity photocathodes have been shown to have a naturally low thermal emittance. However, the thermal emittance depends on the illuminating wavelength; the degree of negative affinity; and the band structure of the photocathode material. As part of the development of a high brightness, high average current photoemission electron gun for the injector of an ERL light source, we have measured the thermal emittance from negative affinity GaAs and GaAsP photocathodes. The measurements were made by measuring the electron beam spot size downstream of a counter-wound solenoid lens as a function of the lens strength. Electron beam spot sizes were measured by two techniques - a 20 micron wire scanner, and a CVD diamond screen. Both Gaussian and 'tophat' spatial profiles were used, and measurements were made at several wavelengths. Results will be presented for both cathode types.
Cornell University, Department of Physics, Ithaca, New York
CLASSE, Ithaca
We have constructed a very high voltage photoemission electron gun as the electron source of a high brightness, high average current injector for an energy recovery linac (ERL) synchrotron radiation light source. The source is designed to deliver 100 mA average current in a CW 1300 MHz pulse train (77 pC/bunch). The cathode voltage may be as high as 750 kV. Negative electron affinity photocathodes are employed to obtain small thermal emittances. The electrode structure is assembled without touching any electrode surface. A load-lock system allows cleaning and activation of cathode samples prior to installation in the electron gun. Cathodes are cleaned by heating and exposure to atomic hydrogen, and activated with cesium and nitrogen trifluoride. Two cathode electrode sets, of 316LN stainless steel and Ti4V6Al alloy, have been used. The anode is beryllium. The internal surface of the ceramic insulator of the gun has a high resistivity fired coating, providing a path to drain away charge from field emission. Non-evaporable getters provide a very high pumping speed for hydrogen. Operating experience with this gun will be presented.
CLASSE, Ithaca
Multi-pass, multi-bunch beam-breakup (BBU) can limit the current in linac-based recirculating accelerators. We have therefore made the computation of the transverse and longitudinal BBU-threshold current available in Cornell's main optics design and beam simulation library BMAD. The coupling of horizontal and vertical motion as well as time of flight effects are automatically contained. Subsequently we present a detailed simulation study of transverse and longitudinal BBU in the proposed 5GeV Energy Recovery Linac light source at Cornell University, including the use of frequency randomization, polarized cavities and optical manipulations to improve the threshold current.
The design of insertion device depends on the properties of the permanent magnet material used. While magnetic material properties such as coercive force, residual induction and magnetization variation with temperature are provided by manufacturer, demagnetization caused by radiation can be only roughly estimated based on very few published data. To obtain data which can be reliably used in ERL insertion device design, we irradiated two materials of very different coercive forces and measured their demagnetization as function of radiation dose. For irradiation we used 5GeV electron beam from Cornell 12GeV Synchrotron. Radiation dose was measured using the calorimetric technique. One of the materials was similar to what we plan to use in construction of ERL undulators. Detailed information on experimental setup, radiation dose measurement techniques, results and analysis will be presented.
MAX-lab, Lund
Advanced Design Consulting, Inc, Lansing, New York
ASP, Clayton, Victoria
This paper summarizes the final magnetic measurement for a hybrid wiggler installed at the Australian Synchrotron Project (ASP). This device uses an anti-symmetric, hybrid design with a period of 100 mm and 40 full-strength Vanadium-Permendur poles surrounded by Neodynium-Iron-Boron magnets. It is designed to operate at two gaps with critical energies of 11.4 (14mm) and 9.6 keV (18.16mm) and to have a maximum gap with the field strength By ≤ 50 G. The wiggler's drive mechanism is capable of moving from minimum to maximum gap in 96 seconds. End terminations are designed to maintain the electron trajectory on-axis. The straightness of the electron orbit is controlled by moving the poles vertically and horizontally. The integrated multipoles are controlled over the interval |x| < 25 mm and all gap sizes by moving the side magnets, installing correction magnets at the wiggler entrance and exit and using correction coils. All adjustments have been made using threaded fasteners. No shims have been used.
UCLA, Los Angeles, California
LLNL, Livermore, California
Compton scattering of intense laser pulses with ultra-relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free-electron lasers and laser and plasma based advanced accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described and transverse phase space measurements are presented.
LLNL, Livermore, California
A new class of tunable, monochromatic gamma-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photo-science and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. Key technologies, basic scaling laws, and recent experimental results will be presented, along with an overview of future research and development directions.
LLNL, Livermore, California
Thomson-Scattering based systems offer a path to high-brightness high-energy (> 1 MeV) x-ray & gamma-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to optimize such a device, dubbed the "Thomson-Radiated Extreme X-Ray" (T-REX) source, targeting up to 680 keV photon energy. Such a system requires precise design of the interaction between a high-intensity laser pulse and a high-brightness electron beam. Presented here are the optimal design parameters for such an interaction, including factors such as the collision angle, focal spot size, optimal bunch charge and laser intensity, pulse duration, and laser beam path. These parameters were chosen based on extensive modelling using PARMELA and in-house, well-benchmarked scattering simulation codes. Also discussed are early experimental results from the newly commissioned system.
LLNL, Livermore, California
Frequency upconversion of laser-generated photons by inverse Compton scattering for applications such as nuclear spectroscopy and gamma-gamma collider concepts on the future ILC would benefit from an increase of average source brightness. The primary obstacle to higher average brightness is the relatively small Thomson scattering cross section. It has been proposed that this limitation can be partially overcome by use of laser pulse recirculation. The traditional approach to laser recirculation entails resonant coupling of low-energy pulse train to a cavity through a partially reflective mirror.* Here we present an alternative, passive approach that is akin to "burst-mode" operation and does not require interferometeric alignment accuracy. Injection of a short and energetic laser pulse is achieved by placing a thin frequency converter, such as a nonlinear optical crystal, into the cavity in the path of the incident laser pulse. This method leads to the increase of x-ray/gamma-ray energy proportional to the increase in photon energy in frequency conversion. Furthermore, frequency tunability can be achieved by utilizing parametric amplifier in place of the frequency converter.
* G. Klemz, K. Monig, and I. Will, "Design study of an optical cavity for a future photon-collider at ILC", Nucl. Instrum. Meth. A 564, 212-224 (2006).
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
BESSY GmbH, Berlin
Rome University La Sapienza, Roma
UCLA, Los Angeles, California
Seeded FEL/IFEL techniques can be used for modulation of a relativistic electron beam longitudinally on the radiation wavelength. However, in the 1-10 THz range, which is of particular importance for matched injection of prebunched electrons into a laser-driven plasma accelerating structure, a suitable radiation source is not available. At the UCLA Neptune Laboratory we have built and fully characterized a radiation source tunable in the range of 1-3 THz. The THz pulse is produced by mixing two CO2 laser lines in a noncollinear phase-matched GaAs crystal at room temperature. The crystal is pumped by 200 ns pulses of a dual beam TEA CO2 laser running at 1 Hz. A grating placed in each lasing section allowed to cover the spectral range for the difference frequency from 0.5-4.5 THz with a step of 30-40 GHz. The achieved narrow bandwidth of ~10-5 and the output power of 2kW are sufficient for seeding a single-pass, waveguide FEL amplifier-prebuncher*. These pulses were used to measure the coupling efficiency and the attenuation for different types of THz waveguides and the results will be reported.
* C. Sung et al. "Seeded FEL/IFEL techniques for radiation amplification and electron microbunching in the terahertz range" Phys. Rev. STAB, 2006 (to be published)
UW-Madison/SRC, Madison, Wisconsin
MIT, Cambridge, Massachusetts
The University of Wisconsin-Madison and its partners are developing a design for an FEL operating in the UV to soft x-ray range that will be proposed as a new multidisciplinary user facility. Key features of this facility include seeded, fully coherent output with tunable photon energy and polarization over the range 5 eV to 1240 eV, and simultaneous, independent operation of multiple beamlines. The different beamlines will support a wide range of science from femto-chemistry requiring ultrashort pulses with kHz repetition rates to photoemission and spectroscopy requiring high average flux and narrow bandwidth at MHz rates. The facility will take advantage of the flexibility, stability, and high average pulse rates available from a CW superconducting linac driven by a photoinjector. This unique facility is expected to enable new science through ultra-high resolution in the time and frequency domains, as well as coherent imaging and nano-fabrication. This project is being developed through collaboration between the UW Synchrotron Radiation Center and MIT. We present an overview of the facility, including the motivating science, and its laser, accelerator, and experimental systems.
UW-Madison/SRC, Madison, Wisconsin
MIT, Cambridge, Massachusetts
We present an initial design of the driver for the Wisconsin VUV/Soft Xray FEL facility, which will provide high intensity coherent photons from 5 eV to 1.2 keV. It uses a 2.5 GeV, L-band CW superconducting linac with a 1.7 GeV tap-off to feed the lower energy FELs. In order to support multiple high rep-rate FELs, the average design current is 1 mA. Sub-nanocoulomb bunches with normalized transverse emittances of order 1 micron are generated in a photoinjector for beamlines operating at repetition rates from kHz to MHz. Multi-stage bunch compression provides 1 kA peak current to the FELs, with low energy spread and a suitable current profile. Compressed bunch lengths of several hundred femtoseconds will allow generation of photon pulses in the range 10 to 100 fs using cascaded FELs. Consideration has been given to removing the residual energy chirp from the beam, and minimizing the effects of space charge, coherent synchrotron radiation, and microbunching instabilities. A beam switchyard using RF separators and fast kickers delivers the desired electron bunches to each of the FELs. Details of the design will be presented, including those areas requiring the most development work.
SLAC, Menlo Park, California
* E. Saldin et al, Nucl. Instr. and Meth. A 539, 499 (2005).** A. Zholents, Phys. Rev. ST Accel. Beams 8, 040701 (2005); A. Zholents et al., in Proceedings of FEL2004, 582 (2004).
SLAC, Menlo Park, California
The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at GTF at SLAC, SDL and ATF at BNL and other laboratories, the 1.6cell s-band (2856MHz) gun was chosen to be the best electron source for the LCLS injector, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce nearly-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120Hz and a 140MV/m cathode field, or to an average power dissipation of 4kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results and analysis of these high-power tests will be presented.
SLAC, Menlo Park, California
The field emission was measured during the high-power testing of the LCLS photocathode RF gun. A careful study and analysis of the field emission electrons, or dark current is important in assessing the gun's internal surface quality in actual operation, especially those surfaces with high fields. The charge per 2 microsecond long RF pulse (the dark charge) was measured as a function of the peak cathode field for the 1.6 cell, 2.856GHz LCLS RF gun. Faraday cup data was taken for cathode peak RF fields up to 120MV/m producing a maximum of 0.6nC/RF pulse for a diamond-turned polycrystalline copper cathode installed in the gun. The field dependence of the dark charge is analyzed using a temperature-dependent Fowler-Nordheim (FN) theory to obtain the field enhancement factor and other emitter parameters. Digitized images of the dark charge were taken using a 100 micron thick YAG crystal for a range of solenoid fields to determine the location and angular distribution of the field emitters. The FN plots and emitter image analysis will be described in this paper.
* M. Borland, APS Report LS-287
SLAC, Menlo Park, California
SLAC, Menlo Park, California
SLAC, Menlo Park, California
This paper presents an efficient, RF-coupled, 95-GHz undulatory (snake-like) antenna that can be fabricated using IC technology. While there are many uses for directed power at this frequency our interest is in understanding the propagation of the input power through the circuit and its radiative characteristics for comparison to earlier work in the THz range (see PAC05). 95 GHz was chosen because test equipment was available (WR-10 waveguide and HP network analyzer). Different materials, heights and widths of the circuit were considered on a low-loss, 0.10-mm thick quartz substrate e.g. 0.75 microns of elevated gold corresponding to three skin depths. The design is compared to more conventional RF technology using a low energy, high power electron beam and to higher energy, lower power Smith Purcell gratings and free-electron-lasers (FELs). The FDTD results show narrow-band, 80% radiation efficiency with a dipole-like radiation pattern that is enhanced by adding periods. The radiated power was calculated using two different techniques that agreed quite well i.e. by integrating the far-field Poynting vector as well as subtracting the output power from input power.
SLAC, Menlo Park, California
The LCLS x-ray free electron laser project at SLAC requires 40 undulators: 33 in the beamline, 6 spares, and one reference undulator. A new facility was constructed at SLAC for tuning and fiducializing the undulators. The throughput of the facility must be approximately one undulator per week. Much effort has gone into automating the undulator tuning. Because of tight alignment tolerances, accurate techniques were developed to fiducialize the undulators. The new facility, the tuning techniques, and the fiducialization techniques will be discussed.
Jefferson Lab, Newport News, Virginia
Jefferson Lab, Newport News, Virginia
DESY Zeuthen, Zeuthen
Injector gun design is an iterative process where the designer optimizes a few nonlinearly interdependent beam parameters to achieve the required beam quality for a particle accelerator. Few tools exist to automate the optimization process and thoroughly explore the parameter space. The challenging beam requirements of new accelerator applications such as light sources and electron cooling devices drive the development of RF and SRF photo injectors. RF and SRF gun design is further complicated because the bunches are space charge dominated and require additional emittance compensation. A genetic algorithm has been successfully used to optimize DC photo injector designs for Cornell* and Jefferson Lab**, and we propose studying how the genetic algorithm techniques can be applied to the design of RF and SRF gun injectors. In this paper, we report on the initial phase of the study where we model and optimize gun designs that have been benchmarked with beam measurements and simulation.
* I. Bazarov, et al., "Multivariate Optimization of a High Brightness DC Gun Photoinjector", PRST-AB 2005.** F. Hannon, et al., "Simulation and Optimisation of a 100 mA DC Photoinjector", EPAC 2006.
Jefferson Lab, Newport News, Virginia
Notional designs for ERL-driven high average power free electron lasers often invoke amplifier-based architectures. To date, however, amplifier FELs have been limited in average power output to values several orders of magnitude lower than those demonstrated in optical-resonator based systems; this is due at least in part to the limited electron beam powers available from their driver accelerators. In order to directly contrast the performance available from amplifiers to that provided by high-power cavity-based resonators, we have developed a scheme to test an amplifier FEL in the JLab SRF ERL driver. We describe an accelerator system design that can seamlessly and non-invasively integrate a 10 m wiggler into the existing system and which provides, at least in principle, performance that would support high-efficiency lasing in an amplifier configuration. Details of the design and an accelerator performance analysis will be presented.
Stanford University, Stanford, Califormia
DC photoguns are used to produce high-quality, high-intensity electron beams for accelerator driven applications. Ion bombardment is credited as the major cause of degradation of the photocathode efficiency. Additionally to ions produced in the accelerating cathode-anode gap, the electron beam can ionize the residual gas in the transport line. These ions are trapped transversely within the beam and can drift back to the accelerating gap and contribute to the bombardment rate of the cathode. This paper proposes a method to reduce the flow of ions produced in the beam transport line and drifting back to the cathode-anode gap by introducing a positive potential barrier that repels the trapped ions. The reduced ion bombardment rate and increased life time of photocathodes will reduce the downtime required to service photoinjectors and associated costs.
DESY, Hamburg
Jefferson Lab, Newport News, Virginia
SBUNSL, Stony Brook, New York
BNL, Upton, Long Island, New York
We report recent progress in the development of a hybrid lead/niobium superconducting (SC) injector. The goal of this effort is to produce an all-SC injector with the SCRF properties of a niobium cavity along with the superior quantum efficiency (QE) of a lead photocathode. Two prototype hybrid injectors have been constructed, one utilizing a cavity with a removable cathode plug, and a second consisting of an all-niobium cavity arc-deposited with lead in the cathode region. We present the results of QE measurements on these cavities, along with tests of the effect of the laser on the cavity RF performance.
BNL, Upton, Long Island, New York
We report the experimental characterization of the FEL efficiency enhancement using a tapered undulator in a single-pass seeded FEL amplifier at the NSLS SDL. The last 3 m of the 10 m NISUS undulator was linearly tapered so that the magnetic field strength at the end of the undulator was reduced by 5 %. The FEL energy gain along the undulator was measured for both the tapered and un-tapered undulator. The FEL energy with the taper was measured to be about 3.2 times higher than that without the taper. We also experimentally characterized the spectrum and the transverse distribution of the FEL light for both the tapered and un-tapered undulator. The experimental results are compared with the numerical simulation code, GENESIS 1.3.
BNL, Upton, Long Island, New York
UMD, College Park, Maryland
LANL, Los Alamos, New Mexico
SAIC, Burlington, Massachusetts
A recently developed model* of the emittance and brightness of a photocathode based on the evaluation of the moments of the electron emission distribution function admits an analytical solution for the zero-field and zero-temperature asymptotic model. Here, the model has been extended to account for the critical modifications of temperature and field dependence, which are tied to material issues with the cathode. Temperature impacts the nature of scattering within the photoemitter material and therefore affects quantum efficiency significantly. Field changes the emission probability at the surface barrier, and is particularly important for low work function coatings, as occur for the cesiated surfaces characteristic of our controlled porosity dispenser photocathodes. Extensions of the theoretical models shall be given, followed by an analysis of their comparison with numerical simulations of the intrinsic emittance and brightness of a photocathode. The methodology is designed to facilitate the development of photoemission models into comprehensive particle-in-cell (PIC) codes to address issues otherwise not readily treated, e.g., variation in surface coverage and topology.
* K. L. Jensen, P. G. O'Shea, D. W. Feldman, and N. A. Moody, Applied Physics Letters 89, 224103 (2006).
GSI, Darmstadt
Uppsala University, Uppsala
FZJ, Julich
TSL, Uppsala
Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, Bonn
UU/ISV, Uppsala
GSI, Darmstadt
BINP SB RAS, Novosibirsk
Universita e Politecnico di Bari, Bari
INFN-Bari, Bari
Bari University, Science Faculty, Bari
The Radioactive Ion Beam (RIB) production with ISOL technique should require a charge breeder device to increase the ion acceleration efficiency and reduce greatly the production cost. The "charge breeder" is a device designed to accept RIB with charge state +1 and in order to increase their charge state up to +n. Recently, at the INFN section of Bari first and at LNL (Italy) then, a new charge breeder device, based on an EBIS ion source called BRIC, has been developed. The new feature of BRIC, with respect to the classical EBIS, is given by the insertion, in the ion drift chamber, of a Radio Frequency (RF) - Quadrupole aiming to filtering the unwanted masses and then making a selective more efficient containment of the wanted ions. The RF test measurements for Ar gas confirm, as foreseen by simulation results* that the selective containment can be obtained. More measurements on the selective containment of heavier element ions (more close to the radioactive ion produced with ISOL technique) like Xe are needed to study with more details that effect. In this contribution new measurements on the rf selective containement in BRIC for Xe gas will be presented and discussed.
* V. Variale and M. Claudione, "BRICTEST: a code for charge breeding simulations in RF quadrupolar field", NIM in Phys. res. A 543 (2005) 403-414.
KEK, Ibaraki
JAEA/LINAC, Ibaraki-ken
JAEA, Ibaraki-ken
Utsunomiya University, Utsunomiya
* R. Sonobe, S. Kawata, et. al., Phys. Plasmas 12 (2005) 073104.
BNL, Upton, Long Island, New York
Fermilab, Batavia, Illinois
CERN, Geneva
NASU/INR, Kiev
BINP SB RAS, Novosibirsk
NSCL, East Lansing, Michigan
Fermilab, Batavia, Illinois
LANL, Los Alamos, New Mexico
Rochester University, Rochester, New York
Carbon foils are widely used in charge-exchange injection in high intensity hadron accelerators. There are a variety of physics issues associated with the use of carbon foils, including stripping efficiency, energy deposition, foil lifetime (temperature rise, mechanical stress and buckling), multiple Coulomb scattering, large angle single Coulomb scattering, energy straggling and radiation activation. This paper will give a brief discussion of these issues based on the study of the Proton Driver and experience of the Fermilab Booster. Details can be found in Ref*.
* W. Chou et al., "Transport and Injection of 8 GeV H- Ions," Fermilab-TM-2285 (2007).
Fermilab, Batavia, Illinois
BINP SB RAS, Novosibirsk
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
A 0.1 A, 4.3 MeV DC electron beam is routinely used to cool 8 GeV antiprotons in Fermilab's Recycler storage ring. While the primary function of the electron cooler is to increase the longitudinal phase-space density of the antiprotons, significant transverse cooling rates have been observed as well. Numerical characterization of electron cooling is done by two types of measurements: friction force measurements by the voltage jump method and diffusion/cooling rates measurements. The paper will present the recent measurement results and will compare them to a non-magnetized model.
UMD, College Park, Maryland
The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron beam current is adjustable from 0.7 mA, an emittance dominated beam, to 100 mA, a strongly space charge dominated beam. UMER is addressing issues in beam physics relevant to many applications that require intense beams of high quality such as advanced concept accelerators, free electron lasers, spallation neutron sources, and future heavy-ion drivers for inertial fusion. The primary focus of this presentation is experimental results and improvements in multi-turn operation of the electron ring. Transport of a low current beam over 100 turns (3600 full lattice periods) has been achieved. Results of high current, space charge dominated multi-turn transport will also be presented.
UMD, College Park, Maryland
The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron storage ring has been closed and recent operations have been focused on achieving multi-turn transport. An entire suite of terminal diagnostics is available for time-resolved phase space measurements of the beam. These diagnostics have been mounted and tested at several points on the ring before it was closed. UMER utilizes a unique injection scheme which uses the fringe fields of an offset quadrupole to assist a pulsed dipole in bending the beam into the ring. Similar concepts, along with more traditional electrostatic methods, are being considered for beam extraction. This presentation will focus on the recent efforts to design and deploy these major subsystems required for beam extraction.
CESR-LEPP, Ithaca, New York
Following two decades of operation at 5 GeV beam energy for studies of bottom quark bound states, the Cornell Electron Storage Ring (CESR) converted to 2 GeV operation in 2001 for the purpose of investigating bound states of charm quarks. This reduction of beam energy resulted in increased relative contributions of the beam-beam force. The beam-beam interaction has been found to have considerable consequences for the optics and for the injection aperture. We describe recent developments in our modelling of the beam-beam interaction, experimental validation techniques, and investigations into compensation strategies.
LLNL, Livermore, California
A compact Dielectric Wall Accelerator (DWA), with field gradient up to 100 MV/m, is being developed to accelerate proton bunches for use in cancer therapy treatment. The injector first generates a few nanosecond long and 40 pQ proton bunch, which is then compressed in the compression section at the end of the injector. Finally the bunch is accelerated in the high-gradient DWA accelerator to energy up to 70 - 250 MeV. The Particle-In-Cell (PIC) code LSP is used to model several aspects of this design. First, we use LSP to determine the needed voltage waveform in the A-K gap that will produce a proton bunch with the requisite charge. We then model pulse compression and shaping in the section between the A-K gap and the DWA. We finally use LSP to model the beam transport through the DWA.
LANL, Los Alamos, New Mexico
The aim of the helicon plasma generator-assisted negative ion source development at Los Alamos Neutron Science Center (LANSCE) is to use high-density helicon plasmas for producing intense beams of H- ions. Our work consists of two development paths, construction of a hybrid ion source and replacement of the LANSCE surface converter ion source filaments by helicon plasma generators. The hybrid ion source is a combination of a long-life plasma cathode, sustained by a helicon plasma generator, with a stationary, pulsed main discharge (multi-cusp H- production chamber) directly coupled to each other. The electrons are transferred from the helicon plasma to the cusp-chamber by thermal flow process to ignite and sustain the main discharge. Replacing the filaments of the surface converter source by two helicon plasma generators is a low-cost solution, building upon the well-proven converter-type ion sources. Both development paths are aimed at meeting the beam production goals of the LANSCE 800 MeV linear accelerator refurbishment project. The design and status of both ion source types is discussed.
CERN, Geneva
The ILC positron damping ring comprises hundreds of meters of wiggler sections, where many more photons than in the arcs are emitted, and with the smallest beam-pipe aperture of the ring. A significant electron-cloud density can therefore be accumulated via photo-emission and via beam-induced multipacting. In field-free regions the electron-cloud build up may be suppressed by adding weak solenoid fields, but the electron cloud remaining in the wigglers as well as in the arc dipole magnets can still drive single-bunch and multi-bunch beam instabilities. This paper studies the electron-cloud formation in an ILC wiggler section for various scenarios, as well as its character, and possible mitigation schemes.
Far-Tech, Inc., San Diego, California
Electron cyclotron resonance ion sources (ECRIS) that generate multiply charged ions reduce the cost to produce radioactive ion beams by reducing the accelerating voltage needed to achieve the desired beam energy. FAR-TECH, Inc. is developing an integrated suite of numerical codes to simulate ECRIS ion capture, charge breeding, and ion extraction. Ion extraction is modeled with a particle in cell (PIC) code. Since the ion dynamics are strongly dependent on the behavior of the plasma sheath at the boundary between the ECRIS plasma and the ion optics, the PIC code uses an adaptive Poisson solver to accurately resolve the potential drop in the sheath. Results of the integrated ECRIS model will be presented, including calculations of extraction efficiency with multiple ion species.
Far-Tech, Inc., San Diego, California
ANL, Argonne, Illinois
UW-Madison/PD, Madison, Wisconsin
The electron cyclotron-resonance ion source (ECRIS) is one of the most efficient ways to provide high-quality, high-charge-state ion beam for research and development of particle accelerators and atomic physics experiments. For ECR ion source performance optimization, FAR-TECH Inc. is developing an integrated suite of computer codes: the Generalized ECRIS plasma Modeling code (GEM), the MCBC (Monte Carlo Beam Capture) module, to study beam capture and charge-breeding processes in ECRIS, and the extraction section code. Our recent progress includes the following: algorithm update of Coulomb collision in MCBC for more accurate calculations of the beam capture efficiency, which depends on beam energy and the background plasma, 2D extension of GEM by adding the radial dimension, and the ion extraction section modeling using an adaptive technique.
Far-Tech, Inc., San Diego, California
To model ECRIS, GEM is being extended to 2D by adding radial dimension. The electron distribution function (EDF) is calculated on each magnetic flux surface using a bounce-averaged Fokker-Planck code with 2D ECR heating (ECRH) modeling. The ion fluid model is also being extended to 2D by adding collisional radial transport terms. All species in ECRIS are balanced by keeping the neutrality in each cell and the plasma potential is calculated by maintaining the ambipolarity globally. The graphical user interface (GUI) and parallel computing ability of GEM make it an easy-to-use tool for ECRIS research. Numerical results and comparisons with experimental data will be presented.
BNL, Upton, Long Island, New York
Beam-beam effects present one of major factors limiting the luminosity of colliders. In the linac-ring option of eRHIC design, an electron beam accelerated in a superconducting energy recovery linac collides with a proton beam circulating in the RHIC ring. There are some features of beam-beam effects which require careful examination in linac-ring configuration. First, the beam-beam interaction can induce specific head-tail type instability of the proton beam referred to as kink instability. Thus, beam stability conditions should be established to avoid proton beam loss. Also, the electron beam transverse disruption by collisions has to be evaluated to ensure beam quality is good enough for the energy recovery pass. In addition, fluctuations of electron beam current and/or electron beam size, as well as transverse offset, can cause proton beam emittance growth. The tolerances for those factors should be determined and possible countermeasures should be developed to mitigate the emittance growth. In this paper, a soft Gaussian strong-strong simulation is used to study all of mentioned beam-beam interaction features and possible techniques to reduce the emittance growth.
BNL, Upton, Long Island, New York
There is significant interest in RHIC heavy ion collisions at c.m. energies of 5-50 GeV/u, motivated by a search for the QCD phase transition critical point. The low end of this energy range is well below the nominal RHIC injection c.m. energy of 19.6 GeV/u. There are several challenges that face RHIC operations in this regime, including longitudinal acceptance, magnet field quality, lattice control, and luminosity monitoring. We report on the status of work to address these challenges and include results from beam tests of low-energy RHIC operations with protons and gold.
BNL, Upton, Long Island, New York
The beam emittance growth in RHIC polarized proton runs has a dependence on the dynamic pressure rise, which is caused by the electron cloud and peaked at the end of the beam injection and the early energy acceleration. This emittance growth is usually presented without beam instability, and it is slower than the ones above the instability threshold. The effect on the machine luminosity, nevertheless, is significant, and it is currently a limiting factor in machine performance. The electron cloud is substantially reduced at the store, the emittance growth there has no dependence on the bunch spacing and instead it has a clear dependence on the beam-beam parameter. The results of the machine operation and beam studies will be reported.
Technion, Haifa
Franck and Hertz in 1914 were the first to demonstrate that free electrons can be decelerated by mercury atoms in discrete energy quanta. In 1930 Latyscheff and Leipunsky have demonstrated the inverse effect namely; free electrons can be accelerated by energy stored in the mercury atoms (collision of the second kind). It was only in 1958 that Townes has used multiple collisions between photons and excited atoms to amplify radiation (MASER & LASER). In 1995 Schachter suggested to use excited atoms for coherently accelerate particles. The results of a proof-of-principle experiment (2006) demonstrating the PASER scheme are reported here. Performed at the BNL-ATF, the essence of the experiment is to inject a 45MeV density modulated beam into an excited CO2 gas mixture. Resonance is insured by having the beam bunched by its interaction with a high-power CO2 laser pulse within a wiggler. The electrons experienced 0.15% relative change in their kinetic energy, in less than 40cm long interaction region. The experimental results indicate that a fraction of these electrons have gained 200keV each, implying that such an electron has undergone 2,000,000 collisions of the second kind.
Stanford University, Stanford, Califormia
SLAC, Menlo Park, California
There has been continued interest in the development of dielectric-loaded wakefield structures that can be used to accelerate particle beams. The present search for materials able to withstand very intense RF fields has renewed this interest. Recent experiments at the Argonne Wakefield Accelerator have generated short RF pulses with accelerating fields in excess of 80 MV/m. These experiments used ceramic-lined cylindrical waveguides, operating at frequencies between 10 and 15 GHz. Other important experiments, at different RF frequencies and using planar or cylindrical geometries, have been carried out at various other facilities. A number of new experiments are planned in the near future to explore the capabilities of this class of structures. This presentation will provide an up-to-date survey of the activities in this area of research.
*M. Zolotorev and A. Zholents, Phys Rev. E 50 (1994) 3087.
UCLA, Los Angeles, California
Fermilab, Batavia, Illinois
Rochester University, Rochester, New York
Northern Illinois University, DeKalb, Illinois
Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion. Time resolved measurements of the focused electron bunch are also reported and all results are compared to simulations.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
The costs and the time scales of colliders intended to reach the energy frontier are such that it is important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders. In these accelerators a drive beam, either laser or particle, produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on sustaining ultra-high accelerating fields over a substantial length to achieve a significant energy gain. More than 42 GeV energy gain was achieved in an 85 cm long plasma wakefield accelerator driven by a 42 GeV electron drive beam at the Stanford Linear Accelerator Center (SLAC). Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of ~52 GV/m. This effectively doubles their energy, producing the energy gain of the 3 km long SLAC accelerator in less than a metre for a small fraction of the electrons in the injected bunch.
Tech-X, Boulder, Colorado
University of Nevada, Reno, Reno, Nevada
LBNL, Berkeley, California
OXFORDphysics, Oxford, Oxon
Tech-X, Boulder, Colorado
University of Nevada, Reno, Reno, Nevada
LBNL, Berkeley, California
Laser wakefield accelerators produce accelerating gradients up to hundreds of GeV/m and narrow energy spread, and have recently demonstrated energies up to GeV and improved stability [*,**] using electrons self trapped from the plasma. Controlled injection and staging can further improve beam quality by circumventing tradeoffs between energy, stability, and energy spread/emittance. We present experiments demonstrating production of a stable electron beam near 1 MeV with 100 keV level energy spread and central energy stability by using the plasma density profile to control self injection, and supporting simulations. A 10 TW laser pulse was focused near the downstream edge of a mm-long hydrogen gas jet. The plasma density near focus is decreasing in the laser propagation direction, which changes the wake phase velocity and reduces the trapping threshold. This allows stable self trapping and low absolute energy spread. Simulations indicate that such beams can be post accelerated to form high energy, high quality, stable beams, and experiments are under investigation.
* Geddes et al, Nature v431 no7008, 538 (2004).** Leemans et al, Nature Physics v2 no10, p696 (2006)
UCLA, Los Angeles, California
Instituto Superior Tecnico, Lisbon
In a laser wakefield accelerator experiment where the length of the pump laser pulse is several plasma period long, the leading edge of the laser pulse undergoes frequency downshifting as the laser energy is transferred to the wake. Therefore, after some propagation distance, the group velocity of the leading edge of of the pump pulse–and therefore of the driven electron plasma wave–will slow down. This can have implications for the dephasing length of the accelerated electrons and therefore needs to be understood experimentally. We have carried out an experimental investigation where we have measured the velocity vf of the 'wave-front' of the plasma wave driven by a nominally 50fs (FWHM), intense (a0~1), 0.8 micron laser pulse. To determine the speed of the wave front, time- and space-resolved shadowgraphy, interferometry, and Thomson scattering were used. Although low density data (ne ~ 1018 cm-3) showed no significant changes in vf over 1.5mm (and no accelerated electrons), high-density data shows accelerated electrons and an approximately 5% drop in vf after a propagation distance of about 800 microns.
The Fermilab Tevatron Collider Run II program continues at the energy and luminosity frontier of high energy particle physics. The presentation will cover major improvements in the performance of the collider complex which lead to the record-breaking luminosity.
Jefferson Lab, Newport News, Virginia
IUCF, Bloomington, Indiana
BTG, New York
BNL, Upton, Long Island, New York
ANL, Argonne, Illinois
Experiments on the study of fundamental quark-gluon structure of nucleons require an electron-light ion collider of a center of mass energy from 20 to 65 GeV at luminosity level of 1035 cm-2s-1 with both beams polarized. A CEBAF accelerator based ring-ring collider of 7 GeV electrons/positrons and 150 GeV light ions is envisioned as a possible next step after the 12 GeV CEBAF Upgrade. The developed ring-ring scheme takes advantage of the existing polarized continuous electron beam and SRF linac, the green-field design of the collider rings and the ion accelerator complex with electron cooling. We report results of our design studies of the ring-ring version of an electron-light ion collider of the required luminosity.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
ORNL, Oak Ridge, Tennessee
AES, Princeton, New Jersey
Fermilab, Batavia, Illinois
Jefferson Lab, Newport News, Virginia
BINP SB RAS, Novosibirsk
JINR, Dubna, Moscow Region
The physics interest in a luminosity upgrade of RHIC requires the development of a cooling-frontier facility. Detailed cooling calculations have been made to determine the efficacy of electron cooling of the stored RHIC beams. This has been followed by beam dynamics simulations to establish the feasibility of creating the necessary electron beam. Electron cooling of RHIC at collisions requires electron beam energy up to about 54 MeV at an average current of between 50 to 100 mA and a particularly bright electron beam. The accelerator chosen to generate this electron beam is a superconducting Energy Recovery Linac (ERL) with a superconducting RF gun with a laser-photocathode. An intensive experimental R&D program engages the various elements of the accelerator: Photocathodes of novel design, superconducting RF electron gun of a particularly high current and low emittance, a very high-current ERL cavity and a demonstration ERL using these components.
SLAC, Menlo Park, California
JAI, Oxford
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
An undulator based positron source allows generation of polarized positrons in quantities required by ILC. Here we describe the results of modeling and testing of elements for such a system.
ORNL, Oak Ridge, Tennessee
LBNL, Berkeley, California
LANL, Los Alamos, New Mexico
IUCF, Bloomington, Indiana
SLAC, Menlo Park, California
UW-Madison, Madison, Wisconsin
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This talk describes the system configuration, results of several experimental tests and studies of system optimization along with studies of the factors limiting its performance.
SLAC, Menlo Park, California
PSI, Villigen
Possible remedies for the electron cloud in the Damping Ring of the International Linear collider includes conditioning of the surface and chamber with grooves. We installed chambers in PEP-II to test the secondary electron yield (SEY) of coated TiN and TiZrV NEG samples and study the effect of electron and photon conditioning in situ. We have also installed vacuum chambers with rectangular groove profile in straight sections to test this possible mitigation technique. In this paper, we will describe the PEP-II test layout, results and impact on impedance.
Eisenwerke Fried. Wilh. Dueker GmbH & Co. KGaA, Laufach
Clausthal, Inst für Nichtmetall. Werkstoffe, Clausthal-Zellerfeld
CERN, Geneva
Wendel GmbH, Dillenburg
Fermilab, Batavia, Illinois
The more beam is cooled, the less stable it is. In the Recycler Ring, antiprotons are cooled both with stochastic and electron cooling. To stabilize it against the resistive wall instability, a digital damper is successfully used. Digital dampers can be described as linear operators with explicit time dependence, and that makes a principle difference with analogous dampers. Theoretical description of the digital dampers is presented. Electron cooling makes possible a two-beam instability of the cooled beam with the electron beam. Special features of this instability are described, and the remedy is discussed.
SOLEIL, Gif-sur-Yvette
UMD, College Park, Maryland
A common challenge for accelerator systems is to maintain beam quality and brightness over the usually long distance from the source to the target. In order to do so, knowledge of the beam distribution in both configuration and velocity space along the beam line is needed. However, measurement of the velocity distribution can be difficult, especially for beams with strong space charge. Here we present a simple and portable tomographic method to map the beam phase space, which can be used in the majority of accelerators. The tomographic reconstruction process has first been compared with results from simulations using the particle-in-cell code WARP. Results show excellent agreement even for beams with extreme space charge and exotic distributions. Our diagnostic has also been successfully demonstrated experimentally on the University of Maryland Electron Ring, a compact ring designed to study the transverse dynamics of beams in both emittance and space charge dominated regimes. Special emphasis is given to intense beams where our phase space tomography diagnostic is used to shed light on the consequences of the space charge forces on the transport of these beams.
MPI-K, Heidelberg
Kyoto ICR, Uji, Kyoto
JINR, Dubna, Moscow Region
NIRS, Chiba-shi
S-LSR is a storage and cooler ring with the circumference of 22.56 m applied for an electron beam cooling of 7 MeV proton beam and laser cooling of 24Mg+ beam with 35 keV. From the measurement with the use of Schottky pich-up of the momentum spread of 7 MeV proton beam reducing the particle number to suppress the effect of intra-beam scattering,abrupt jump in fractional momentum spread and Schottky power has been observed, which is considered the 1 dimensional phase transition to the ordered state*. The situation has also been expected from numerical simulation**. Laser cooling with much stronger cooling force is expected to realize 2Dand 3D crystalline states if the maintenance condition can be satisfied. Experimental approaches to realize such a condition at S-LSR as dispersion free lattice and "tapered cooling" are also decribed in the present paper.
* A Noda, et al., , New Journal of Physics, 8 (2006)288.** A. Smirnov et al., Beam Science and Technology, 10 (2006) 6*** J. Wei, X-P, Li and A. M. Sessler, , Phys. Rev. Lett. 73 (1994) 3089.
Royal Holloway, University of London, Surrey
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
CERN, Geneva
Halo simulations and estimates are important for the design of future linear accelerators. We present simulations performed for the ILC and CLIC and compare these with semi-analytical estimates and other simulations.
BNL, Upton, Long Island, New York
IUCF, Bloomington, Indiana
CRE, Wuppertal
ACCEL, Bergisch Gladbach
DESY, Hamburg
For pump- and probe experiments at VUV- and X-ray free-electron lasers the stability of the electron beam and timing reference must be guaranteed in phase for the injector and bunch compression section within a resolution of 0.01 degree (rms) and in amplitude within 1 10-4 (rms). The performance of the field detection and regulation of the acceleration RF critically influences the phase and amplitude stability. For the RF field control, a multichannel RF downconverter is used to detect the field vectors and control the vectorsum of 32 cavities. In this paper a new design of an 8 channel downconverter is presented. The downconverter frontend consists of a passive rf double balanced mixer input stage, intermediate filters and an integrated 16bit analog-to-digital converter (ADC). The design includes a digital motherboard for data preprocessing and communication with the controller. In addition we characterize the downconverter performance in amplitude and phase jitter, temperature drifts and channel crosstalk in laboratory environment as well as for accelerator operation.
TETD, Otawara
Toshiba, Yokohama
KEK, Ibaraki
IHEP Beijing, Beijing
USTC/NSRL, Hefei, Anhui
We have developed the mathod to determine the permittivity and permeability of Kanthal alloy available. The alloy is coated on the inside walls of disk-loaded cavities,which is used for the collinear load. The collinear load absorbs the remaining rf-power over the last cells of the section while still accelerating the beam. Based on the experimental results of the permittivity and permeability,the computation study of the constant power-loss collinear load has been made by Microwave Studio. The design data about the S-band collinear load are present.
KAERI, Daejon
An elliptical superconducting RF cavity of 700 MHz with βg=0.42 has been designed for the Linac of Proton Engineering Frontier Project (PEFP). A double-ring stiffening structure is used for a low-beta cavity for a Lorentz force detuning. The results of the electron multipacting analysis of the cavity are presented. A HOM analysis shows that the HOM coupler's Qext is lower than 3·10+5, thus reducing the influence of dangerous modes on the beam instabilities and the HOM-induced power.
PAL, Pohang, Kyungbuk
RIST, Pohang
Pohang Accelerator Laboratory has studied SRF cavity and set up SRF test laboratory from January 2006. The first activity for SRF research was to develop SRF 3rd harmonic cavity for Pohang Light Source, which was designed, fabricated and tested in 2006. The cryostat are under design. The fabrication of ICHIRO cavity, which is ILC ACD cavity, is PAL's second activity related to SRF. Deep drawing, trimming and welding by electron beam for a 9-cell ICHIRO cavity were done in PAL. The polishing processes for the RF surface including electropolishing were done in KEK under the collaboration between two institutes. This will be tested with real beam in STF-1 of KEK in second half period of 2007. This paper reports the results of fabrication of ICHIRO single- and nine-cell cavities performed in PAL.
PAL, Pohang, Kyungbuk
Pohang Accelerator Laboratory has prepared to SRF 3rd harmonic cavity to increase beam lifetime and to damp orbit instability by lengthening electron bunch in PLS. The SRF cavity was developed and its vertical test was done already with success. Higher order modes were analyzed to optimize its performance in beam orbit. Most of them are not effective to electron beam, while the others have possibility to impact orbit stability. These harmful HOMs can be removed by HOM absorber installed in beam pipe. This paper reports the HOM analysis and design of its removal system.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
UMAN, Manchester
ANL, Argonne, Illinois
The Phase I Advanced Photon Source Deflecting Cavity System for producing short X-ray pulses uses one multi-cell, S-band cavity to apply a deflecting voltage to the stored electron beam ahead of an undulator that supports a beamline utilizing short picosecond X-rays. Two additional multi-cell cavities are then used to cancel out the perturbation and redirect the electron beam along the path of its nominal orbit. The pulsed rf system driving the deflecting cavities is described. Design tradeoffs are discussed with emphasis on topology considerations and digital control loops making use of sampling technology in a manner consistent with the present state of the art.
IIT, Chicago, Illinois
Tech-X, Boulder, Colorado
Recent experimental work done to develop high gradient, low frequency cavities for muon cooling, has led to a model of rf breakdown and high gradient limits in warm structures. We have recently been extending this model to try to explain some superconducing rf quench mechanisms, as well as DC and dielectric breakdown. The model assumes that the dominant mechanisms in warm metal systems are fractures caused by the the electric tensile stress, and surface micro-topography that is strongly determined by the the cavity design and history*. We describe how these processes can determine all measurable parameters in warm systems. With superconducting systems, these mechanisms also apply, however field emission, impurities and temperature produce a somewhat different picture of quenching and pulsed power processing. We describe the model and some recent extensions and improvements in some detail and a variety of results accelerators and other applications.
* Hassanein et. al. Phys. Rev. STAB, 9, 062001
Fermilab, Batavia, Illinois
As part of the research and development towards the International Linear Collider (ILC), several test facilities have been developed at Fermilab. This paper presents the latest LLRF results obtained with Capture Cavity II at these test facilities. The main focus will be on controls and RF operations using the SIMCON based LLRF system. Details about hardware upgrades and overall system performance will be also explained. Finally, design considerations and objectives for the future test facility at the New Muon Laboratory (NML) will be presented.
STAR, Inc., Mequon, Wisconsin
Fermilab, Batavia, Illinois
Rutgers University, The State University of New Jersey, Piscataway, New Jersey
Fermilab, Batavia, Illinois
Valuable experience in operating and maintaining superconducting RF cavities in a horizontal test module has been gained with Capture Cavity II. We report on all facets of our experience to date.
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
Illinois Institute of Technology, Chicago, Illinois
The FLASH user facility providing free electron laser radiation is built based on the TTF project at DESY. Fermilab has the responsibility for the design and processing of a third harmonic, 3.9 GHz, superconducting cavity which is powered via a coaxial power coupler. Six power couplers have been manufactured at CPI after successful design of the power coupler including RF simulation, multipacting calculation, and thermal analysis. The power couplers are being tested and processed with high pulsed power in an elaborate test stand at Fermilab now. This paper presents the RF design and processing work of the power coupler.
MIT/PSFC, Cambridge, Massachusetts
A concept for a high-power ribbon-beam klystron (RBK) employing a novel large-aspect ratio elliptic electron beam instead of a conventional circular electron beam is presented. Both cold-fluid and kinetic equilibrium theories are developed and applied in the design of the elliptic electron beam for the RBK. A small-signal theory is developed and applied in the design of the beam tunnel and the input, idler and output cavities. The electron gun and beam matching is being studied. Design results of a 10 MW 1.3 GHz RBK for the International Linear Collider (ILC) and of a 50 MW 22 GHz RBK for high-gradient research will be discussed.
UMD, College Park, Maryland
The University of Maryland Electron Ring (UMER) is a scaled storage ring using low-energy electrons to inexpensively model beams with high-space-charge. With the ability to inject such beams comes the problem of longitudinal end erosion of both the head and tail. It is important therefore to apply suitably designed longitudinal focusing forces to confine the beam and prevent it from its normal expansion. This paper presents the design and prototyping of an induction cell for this purpose. Successful operation of the induction cell would push the achievable number of turns and also enable us to perform studies of the longitudinal physics of such highly space-charge dominated beams. The pulsed voltage requirements for such a system on UMER would require ear-fields that switch 3kV in about 8ns or so for the most intense flat-top rectangular beam injected into the ring. This places a considerable challenge on the electronics used to deliver ideal waveforms with a compact module. Alternate waveforms are also being explored for other various injected beam shapes into UMER.
CLASSE, Ithaca
Based on the encouraging results of the first 1300 MHz 70 mm aperture single cell re-entrant cavities*, we continue the high gradient studies for ILC with new re-entrant cavities made of fine-grain as well as large-grain niobium. These new cavities have smaller aperture of 60 mm, providing a further reduced Hpk/Eacc or a further improved ultimate gradient. Four 1300 MHz 60 mm aperture re-entrant cavities are made, two out of fine grain niobium and the other two out of large-grain niobium. In addition, two elliptical shape 1500 MHz cavities are also made out of large-grain niobium. We present the testing results of these cavities.
* R. L. Geng et al., PAC2005, p.653.
CLASSE, Ithaca
Six 1300 MHz superconducting niobium 2-cell cavities are manufactured for the prototype of Cornell ERL injector to boost the energy of a high current, low emittance beam produced by a DC gun. Designed for high current beam acceleration, these cavities have new characteristics as compared to previously developed low-current cavities such as those for TTF. Precision manufacture is emphasized for a better straightness of the cavity axis so as to avoid unwanted emittance dilution. We present the manufacturing, processing and vertical test performance of these cavities. We also present the impact of new cavity characteristics to the cavity performance as learnt from vertical tests. Solutions for improving cavity performance are discussed.
Cornell University, Ithaca, New York
CLASSE, Ithaca
Electropolishing is now the preferred method for chemical treatment of niobium cavity surfaces. It provides a very smooth surface and after baking accelerating fields between 35 - 40 MV/m. However the reproducibility of performance needs to be improved substantially. Some of the leading causes are related to contaminant residues after electropolishing, these include sulphur particles, niobium pentoxide particles and traces of aluminum from reaction between the aluminum cathode and the acid electrolyte. We have carried out studies to enhance the deposition of such particles so that we can isolate and study the residues. We will present analysis of these studies using optical microscopy, SEM, and Auger. In at attempt to dissolve these contaminants, we have also conducted studies on the effectiveness of various rinsing agents, such as degreasing agents, dilute HF, hydrogen peroxide.
CLASSE, Ithaca
Cornell University, Ithaca, New York
As the surface magnetic field in niobium cavities approaches the theoretical critical field, rf losses begin to grow sensitive to increasingly subtle features of the material and the surface. A striking example is the familiar occurrence of the high-field Q-slope, where rf losses increase exponentially with field above an onset field. A surprising feature of the high-field Q slope is its positive response to mild baking at 120 C. But the Q-slope returns after the first 20 nm of the niobium metal surface is converted to loss-less pentoxide via anodization, a key feature. The latter result suggests that the cause of the fast growing losses resides in the first 20 nm of the rf surface. Although there are several propositions, the exact mechanism for the high-field Q-slope is not yet fully understood and demands further research. We are conducting surface analytic studies with XPS, SIMS, and Auger to shed light on the mechanism of the high-field Q-slope. We are comparing the behavior of fine-grain samples with single crystal samples, BCP treatments with EP treatments and properties before and after 120 C bake. We also study the effect of baking at temperatures up to 400 C.
LLNL, Livermore, California
University of Missouri - Rolla, Rolla, Missouri
As part of our ongoing development of the Dielectric Wall Accelerator, we are studying the performance of multilayer high-gradient insulators. These vacuum insulating structures are composed of thin, alternating layers of metal and dielectric, and have been shown to withstand higher gradients than conventional vacuum insulator materials. This paper describes these structures and presents some of our recent results.
LLNL, Livermore, California
The now-mature FXR (Flash X-Ray) radiographic facility at Lawrence Livermore National Laboratory will be briefly described with emphasis on its pulsed power system. The heart of each accelerating cell's pulse-forming Blumlein is it's sulfur hexafluoride-based triggered closing switch. FXR's recent upgrade to a recirculating SF6 gas reclamation system will be described and the resulting accelerator performance and reliability improvements documented. This was accompanied by a detailed switch breakdown study on FXR's Test Stand* and the recent analysis of the resulting statistics will be shown.
* W. DeHope, D. Goerz, R. Kihara, M. Ong, G. Vogtlin, J. Zentler, "An Induction Linac Test Stand", 21st Particle Accelerator Conference, Knoxville, TN, May 20, 2005
SAIC, Alamo, California
LLNL, Livermore, California
LBNL, Berkeley, California
The Pulse-Line Ion Accelerator* (PLIA) is a helical distributed transmission line. A rising pulse applied to the upstream end appears as a moving spatial voltage ramp, on which an ion pulse can be accelerated. This is a promising approach to acceleration and longitudinal compression of an ion beam at high line charge density. In most of the studies carried out to date, using both a simple code for longitudinal beam dynamics and the Warp PIC code, a circuit model for the wave behavior was employed; in Warp, the helix I and V are source terms in elliptic equations for E and B. However, it appears possible to obtain improved fidelity using a "sheath helix" model in the quasi-static limit. Here we describe an algorithmic approach that may be used to effect such a solution.
*R. J. Briggs, PRST-AB 9, 060401 (2006).
SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
Fundamental power couplers for superconducting accelerator applications like the ILC are complicated RF transmission line assemblies due to their having to simultaneously accommodate demanding RF power, cryogenic, and cleanliness constraints. When these couplers are RF conditioned, the observed response is an aggregate of all the parts of the coupler and the specific features that dominate the conditioning response are unknown. To better understand and characterize RF conditioning phenomena toward improving performance and reducing conditioning time, a high-power coupler component test stand has been built at SLAC. Operating at 1.3 GHz, this test stand was designed to measure the conditioning behavior of select components of the TTFIII coupler independently, including outer-conductor bellows, diameter changes, copper plating and surface preparations, and cold window geometries and coatings. A description of the test stand, the measurement approach, and a summary of the results obtained are presented.
LANL, Los Alamos, New Mexico
NSTec, Los Alamos, New Mexico
SAIC, Los Alamos, New Mexico
LANL, Los Alamos, New Mexico
We propose to use the photonic band gap (PBG) structures for the construction of a traveling-wave tube (TWT) at W-band. Interest in millimeter-waves has increased in recent years due to applications in environmental monitoring and remote sensing. The development of wide-band mm-wave TWT amplifiers is underway at Los Alamos National Laboratory. A TWT would present a wide bandwidth source for remote mm-wave spectroscopy. PBG TWT structures have great potential for very large bandwidth and linear dispersion. In addition, being cheap to fabricate, the PBG structures enhance the commercial transferability of the W-band TWT technology. We employ an omniguide which is a one-dimensional version of the PBG structure representing a periodic system of concentric dielectric tubes as a slow-wave structure. A silica omniguide was designed to support a TM01-like mode with a phase velocity matching the one of a 120keV electron beam. The structure was fabricated, cold-tested and installed at our laboratory for the hot test.
UCLA, Los Angeles, California
RadiaBeam, Los Angeles, California
The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, the full cell geometry must be changed significantly. We report on a method of accomplishing this, in which we use a mechanical device of custom design to stretch the cavity structure of an existing photoinjector in order to tune the resonant frequency up by over 2 MHz. We present results of testing the modified photoinjector in an RF test bed with both copper and magnesium cathodes, succeeding in putting approximately 8 - 10 MW of RF power into the gun. This is an improvement over the 4 MW routinely achieved in a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory.
ANL, Argonne, Illinois
SLAC, Menlo Park, California
LLNL, Livermore, California
The TTF-III coupler adopted for the ILC baseline cavity design has shown a tendency to have long initial high power processing times. A possible cause for the long processing times is believed to be multipacting in various regions of the coupler. To understand performance limitations during high power processing, SLAC has built a flexible high-power coupler test stand. The plan is to test individual sections of the coupler, which includes the cold and warm coaxes, the cold and warm bellows, and the cold window, using the test stand to identify problematic regions. To provide insights for the high power test, detailed numerical simulations of multipacting for these sections will be performed using the 3D multipacting code Track3P. The simulation results will be compared with measurement data.
Omega-P, Inc., New Haven, Connecticut
KEK, Ibaraki
A relatively simple and inexpensive two-cavity 45 MW, 22.8 GHz second-harmonic multiplier is considered as an RF source for High-Gradient experiments. The design is to be based on use of an existing SLAC electron gun, such as the XL-4 gun. RF drive power would be supplied from a 50 MW SLAC klystron and modulator, and a second modulator would be used to power the gun in the multiplier. An important feature of the harmonic multiplier is TE 01 circular waveguide for output RF power extraction.
AMAC, Newport News, Virginia
MIT, Cambridge, Massachusetts
There is an increasing demand for High beam Current, high Radio-Frequency (RF) power S-band cavities in existing and new accelerator projects to produce a very brilliant, broadband, teraherz coherent synchrotron radiation source (CRS). To achieve this goal, the RF cavities must be upgraded to a gap voltage of 1.5 MV in the limited space available in the machine with a high gradient superconducting cavity. At the present time there are no cavities and accessories designed to support the high beam currents of up to 100 mA and at the same time provide a high gap voltage at such a high S-band frequency. AMAC proposed a High Current, Large Aperture, Low HOM, Single Crystal Nb 2.85GHz Superconducting Cavity with high RF Power Coupler and HOM absorber device. Comprehensive simulation and optimization to determine the SRF cavity parameters to meet the requirements, provided two alternate designs for the RF input couplers, performed a detailed Higher Order Modes (HOM) analysis, and proposed an HOM absorber concept to dampen the modes exited in the cavity due to the high beam current and high bunch intensity.
AMAC, Newport News, Virginia
Fermilab, Batavia, Illinois
In order to increase the protons energy up to 8 GeV in a driver Linac, the particles must be accelerated through various stages and three different power levels (25kW, 100kW and 210kW) are required for the 325 MHz Fermilab Proton Driver couplers. The problem identified by the project is that no High RF power coupler for these cavities has ever been produced using US industrial capabilities. AMAC proposed a novel resolution by development of innovative modular, multiple power levels, 325 MHz spoke cavities power couplers, which to meet three type cavities with one coupler design. The simulation and concept design are presented. The results of HFSS, MAFIA, ANSYS, and Multipacting are also discussed.
Jefferson Lab, Newport News, Virginia
The Thomas Jefferson National Accelerator Facility has begun a cryomodule refurbishment project. The goal of this project is robust 6 GeV, 5 pass operation of the Continuous Electron Beam Accelerator Facility (CEBAF). The scope of the project includes removing, refurbishing and replacing 10 CEBAF cryomodules at a rate of three per year. Refurbishment includes reprocessing of SRF cavities to eliminate field emission and increase the nominal gradient from the original 5 MV/m to 12.5 MV/m. New "dogleg" couplers between the cavity and helium vessel flanges will intercept secondary electrons that produce arcing on the 2 K ceramic window in the Fundamental Power Coupler (FPC). Modification of the Qext of the FPC will allow higher gradient operations. Other changes include new ceramic RF windows for the air to vacuum interface of the FPC and improvements to the mechanical tuners. Any damaged or worn components will be replaced as well. Currently, the first of the refurbished cryomodules has been installed and tested both in the Cryomodule Test Facility and in place in the North Linac of CEBAF. This paper will summarize the results of these tests.
Jefferson Lab, Newport News, Virginia
We have developed a digital process that emulates an analog oscillator and ultimately a self excited loop (SEL) for field control. The SEL, in its analog form, has been used for many years for accelerating cavity field control. In essence the SEL uses the cavity as a resonant circuit – much like a resonant ?tank? circuit is used to build an oscillator. An oscillating resonant circuit can be forced to oscillate at different, but close, frequencies to resonance by applying a phase shift in the feedback path. This allows the circuit to be phased locked to a master reference, which is crucial for multiple cavity accelerators. For phase and amplitude control the SEL must be forced to the master reference frequency, and feedback provided for in both dimensions. The novelty of this design is in the way digital signal processing (DSP) is structured to emulate an analog system. While the digital signal processing elements are not new, to our knowledge this is the first time that the digital SEL concept has been designed and demonstrated. This paper reports on the progress of the design and implementation of the digital SEL for field control of superconducting accelerating cavities.
Jefferson Lab, Newport News, Virginia
DESY, Hamburg
Several, partially successful attempts have been made to develop a superconducting connection between adjacent niobium cavities with the capability to carry up to 30 mT of the magnetic flux. Such a connection would be particularly of great benefit to layouts of long accelerators like ILC because it would shorten the distances between structures and therefore the total length of an accelerator with the associated cost reductions. In addition the superconducting connection would be ideal for a super-structure, two multi-cell cavities connected through a half wavelength long beam pipe providing the coupling. Two welded prototypes of super-structure have been successfully tested with the beam at DESY. The chemical treatment and water rinsing was rather complicated for these prototypes. We have engaged in a program to develop such a connection based on the Nb55Ti material. Several options are pursued such as e.g.a two-cell cavity is being used to explore the reachable magnetic flux for the TESLA like connection with a squeezed niobium gasket between the flanges. In this contribution we will report about the progress of our investigations.
Jefferson Lab, Newport News, Virginia
JLAB, Newport News, Virginia
In a previous paper the cavity* design for an Ampere-class cryomodule was introduced. We have since fabricated a 1500 MHz version of a single cell cavity with waveguide couplers for HOM and fundamental power, attached to one end of the cavity, a 5-cell cavity made from large grain niobium without couplers and a complete 5-cell cavity from polycrystalline niobium featuring waveguide couplers on both ends. A 750 MHz single cell cavity without endgroups has also been manufactured to get some information about obtainable Q-values, gradients and multipacting behavior at lower frequency. This contribution reports on the various tests of these cavities.
* R. A.Rimmer et al.; EPAC 2006, paper MOPCH182
Muons, Inc, Batavia
Fermilab, Batavia, Illinois
Old Dominion University, Norfolk, Virginia
Illinois Institute of Technology, Chicago, Illinois
Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 800 MHz RF cavity experiments are used to investigate the mechanism of RF breakdown. The images show evidence for melting and boiling in small regions of ~10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces are compared to the maximum surface gradient E predicted by an ANSYS model of the cavity. The surface local density of spark remnants, presumably the probability of breakdown, shows a power law dependence on the maximum gradient, with E10 for tungsten and molybdenum and E7 for beryllium. This is reminiscent of Fowler-Nordheim behavior of electron emission from a cold cathode, which is explained by the quantum-mechanical penetration of a barrier that is characterized by the work function of the metal.
ORNL, Oak Ridge, Tennessee
The cryomodule tests are on going to have better understandings of physics as a whole and eventually to provide safe and reliable operation for neutron production. Some features are revealed to be interesting issues and need more attentions than expected, such as operating condition, collective effects between cavities, HOM coupler issues, end-group stability, cavity-coupler interactions, and vacuum/gas physics, waiting for more investigations. Up to now SNS cryomodules were mainly tested at 4.4 K, 10 pulse per second (pps) and 30 pps/60 pps tests are under progress. This paper presents the experiences and the observations during tests of cryomodules.
ANL, Argonne, Illinois
Euclid TechLabs, LLC, Solon, Ohio
KEK, Ibaraki
BNL, Upton, Long Island, New York
Jefferson Lab, Newport News, Virginia
One of the key components for the Energy Recovery Linac being built by the Electron cooling group in the Collider Accelerator Department is the 5 cell accelerating cavity which is designed to accelerate 2 MeV electrons from the gun up to 15-20 MeV, allow them to make one pass through the ring and then decelerate them back down to 2 MeV prior to sending them to the dump. This cavity was designed by BNL and fabricated by AES in Medford, NY. Following fabrication it was sent to Thomas Jefferson Lab in VA for chemical processing, testing and assembly into a string assembly suitable for shipment back to BNL and integration into the ERL. The steps involved in this processing sequence will be reviewed and the deviations from processing of similar SRF cavities will be discussed. The lessons learned from this process are documented to help future projects where the scope is different from that normally encountered.
BNL, Upton, Long Island, New York
AES, Princeton, New Jersey
Jefferson Lab, Newport News, Virginia
The multipacting phenomena in accelerating structures and coaxial lines are well documented and methods of mitigating or suppressing it are understood. The multipacting that occurs in a quarter wave choke joint designed to mount a cathode insertion stalk into a superconducting RF photoinjector has been analyzed via calculations and experimental measurements and the effect of introducing multipacting suppression grooves into the structure is analyzed. Several alternative choke joint designs are analyzed and suggestions made regarding future choke joint development. Furthermore, the problems encountered in cleaning the choke joint surfaces, factors important in changes to the secondary electron yield, are discussed and evaluated. This design is being implemented on the BNL 1.3 GHz photoinjector, previously used for measurement of the quantum efficiency of bare Nb, to allow for the introduction of other cathode materials for study, and to verify the design functions properly prior to constructing our 703 MHz photoinjector with a similar choke joint design.
BNL, Upton, Long Island, New York
L-3, Williamsport, Pennsylvania
* M. F. Kirshner et al., "Apparatus and method for trajectory modulation of an electron beam," U. S. Provisional Patent Application 60/838,580, August 17, 2006. Cleared by DoD/OFOISR for public release under 07-S-0493 on January 22, 2007
DESY, Hamburg
Jefferson Lab, Newport News, Virginia
ACCEL, Bergisch Gladbach
ORNL, Oak Ridge, Tennessee
BINP SB RAS, Novosibirsk
LJW, Saint Louis
Thin carbon foils are used as strippers for charge exchange injection into high intensity proton rings. However, the stripping foils become radioactive and produce uncontrolled beam loss, which is one of the main factors limiting beam power in high intensity proton rings. Recently, we presented a scheme for laser stripping an H- beam for the Spallation Neutron Source ring. First, H- atoms are converted to H0 by a magnetic field, then H0 atoms are excited from the ground state to the upper levels by a laser, and the excited states are converted to protons by a magnetic field. In this paper we report on the first successful proof-of-principle demonstration of this scheme to give high efficiency (around 90%) conversion of H- beam into protons at SNS in Oak Ridge. The experimental setup is described, and comparison of the experimental data with simulations is presented. In addition, future plans on building a practical laser stripping device are discussed.
ORNL, Oak Ridge, Tennessee
RAS/INR, Moscow
SNS Linac utilizes several accelerating structures operating at two frequencies. CCL and SCL operate at 805 MHz while 402.5 MHz is used for RFQ and DTL. Beam transfer from the previous part of the accelerator to the subsequent one requires careful longitudinal matching to improve beam transmission and to minimize beam losses. Longitudinal beam parameters have been investigated with the help of three Bunch Shape Monitors installed in the intersegments of the first CCL Module. The results of bunch shape observations for different accelerator settings are presented. Longitudinal beam emittance has been measured and optimized. Longitudinal beam halo has been evaluated as well.
JAI, Egham, Surrey
KEK, Ibaraki
Royal Holloway, University of London, Surrey
OXFORDphysics, Oxford, Oxon
The ATF extraction line laser-wire (LW) aims to achieve a micron-scale laser spot size and to verify that micron-scale beam profile measurements can be performed at the International Linear Collider beam delivery system. Recent upgrades to the LW system are presented together with recent results including the first use of the LW as a beam diagnostic tool.
DESY, Hamburg
Fermilab, Batavia, Illinois
SLAC, Menlo Park, California
CEA, Gif-sur-Yvette
It is well known that an electron beam excites Higher Order Modes (HOMs) as it passes through an accelerating cavity~[panofsky68]. The properties of the excited signal depend not only on the cavity geometry, but on the charge and trajectory of the beam. It is, therefore, possible to use these signals as a monitor of the beam's position. Electronics were installed on all forty cavities present in the FLASH~[flashref] linac in DESY. These electronics filter out a mode known to have a strong dependence on the beam's position, and mix this down to a frequency suitable for digitisation. An analysis technique based on Singular Value Decomposition (SVD) was developed to calculate the beam's trajectory from the output of the electronics. The entire system has been integrated into the FLASH control system.
Jefferson Lab, Newport News, Virginia
UMD, College Park, Maryland
Optical Transition Radiation Interferometry (OTRI) has proven to be effective tool for measuring rms beam divergence. We present rms emittance measurement results of the 115 MeV energy recovery linac at the Thomas Jefferson National Laboratories Free electron Laser using OTRI. OTRI data from both near field beam images and far field angular distribution images give evidence of two spatial and angular distributions within the beam. Using the unique features of OTRI we segregate the two distributions of the beam and estimate separate rms emittance values for each component.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
LBNL, Berkeley, California
By analysing the pulse to pulse intensity fluctuations of the radiation emitted by a charge particle in the incoherent part of the spectrum, it is possible to extract information about the spatial distribution of the beam. At the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory, we have developed and tested a simple scheme based on this principle that allows for the absolute measurement of the bunch length. A description of the method and the experimental results are presented.
MHI, Kobe
CPI, Palo Alto, California
* A. Balkcum, et al. "Operation of a 1.3 GHz Multiple Beam Klystron," Proc. of 6th IVEC, pp. 505, Noordwijk (2005).
CPI, Beverley, Massachusetts
TETD, Otawara
Toshiba, Yokohama
IF-UFRGS, Porto Alegre
In the present analysis we study the self consistent propagation of nonlinear electromagnetic pulses in a one dimensional relativistic electron-ion plasma, from the perspective of nonlinear dynamics. We show how a series of Hamiltonian bifurcations give rise to the electric fields which are of relevance in the subject of particle acceleration. Nonlinear coupling of plasma waves and electromagnetic pulses triggers strong chaotic dynamics which may detrap the plasma wave from the electromagnetic pulse, leading to wave breaking. Connections with results of earlier analysis are discussed.
LAL, Orsay
ACCEL, Bergisch Gladbach
DESY, Hamburg
Ion effects are detrimental to the performance of the electron damping ring for the International Linear Collider (ILC). Irregular bunch patterns, e.g. short bunch trains with interleaved gaps, are an effective way to alleviate ion effects. In this paper, we discuss the fill patterns and their impact on the ion effects for the ILC electron damping ring.
UOR, Jaipur
Atomic force microscopy (AFM) study of low energy (10 keV) electron beam irradiated Polymethylmethacrylate (PMMA)20 micron thick surface was performed. PMMA film has been used in lithography applicatiion by this technique. AFM in tapping mode has been utilized to investigate the morphological changes on the samples surface as a function of fluence. TM-AFM showed the hills of the nano size surrounded by the craters type features in all the irradiated samples. The shape and size of these features varied with fluence. The root-mean-square (rms) surface roughness of the samples changed from 2.666 nm to 5.617 nm with fluence from 2x1014 electrons/cm2 to 1x1016 electrons/cm2. It shows that roughness increases as increasing fluence.
UCLA, Los Angeles, California
INFN - Gruppo Messina, S. Agata, Messina
Universita di Messina, Messina
Universita di Messina, Messina
INFN - Gruppo Messina, S. Agata, Messina
INFN/LASA, Segrate (MI)
Based on our experience on photocathode production, we present in this paper the results of the application of different optical diagnostic techniques on fresh and used photocathodes. These techniques allow to study effects like non uniformity, cathode aging, etc. In particular, photocathode optical parameters and QE characterization, both done at different wavelengths, give fundamentals information for the construction of a model of the photoemission process to be applied to Cs2Te photocathodes. These studies are useful for further improving key cathode features, such as its robustness and lifetime as well as to study and control the photocathodes thermal emittance.
KEK, Ibaraki
Nihon Koshuha Co., Ltd., Yokohama
MHI, Hiroshima
RIKEN Spring-8 Harima, Hyogo
C-band (5712-MHz) linac is used as the main accelerator of the Japanese X-FEL facility in SPring-8. Since the C-band linac has high acceleration gradient, our 8-GeV accelerator is compact rather than a conventional S-band accelerator. The system consists of following components; two choke-mode-type 1.8-m accelerating structures, an rf pulse compressor (SLED), a 50-MW klystron, a 100-MW compact modulator, and an rf digital control system. We will use 60 to 70 units for the X-FEL accelerator. Since November 2005, we have operated two C-band units in the 250-MeV FEL prototype accelerator (SCSS). After rf conditioning, the accelerating gradient was achieved to 35-MV/m. We successfully accelerated the electron beam by this gradient of electrical field. In this presentation, we will report the detail of each component and its operation status of the SCSS prototype accelerator.
KEK, Ibaraki
KEK, Ibaraki
IN2P3 IPNL, Villeurbanne
KEK, Ibaraki
TMU, Hatioji-shi, Tokyo
INPR, Tomsk
TPU, Tomsk
SAGA, Tosu
A new tungsten single-crystalline positron target has been successfully employed for generation of the intense positron beam at the KEKB injector linac in September 2006. The target is composed of a tungsten single-crystal with a thickness of 10.5 mm. The positron production target is bombarded at an incident electron energy of 4 GeV, and the produced positrons are collected and accelerated up to the final injection energy of 3.5 GeV in the succeeding sections. A conventional tungsten plate with a thickness of 14 mm has been used previously, and the conversion efficiency (Ne+/Ne-), the ratio between the number of positrons (Ne+) captured in the positron capture section and the number of the incident electrons (Ne-), was 0.20 on average. By replacing the tungsten plate with the tungsten crystal, it increased to 0.25 on average. The increase of the conversion efficiency has boosted the positron intensity to its maximum since the beginning of KEKB operation in 1999. Now this new positron source is stably operating and is contributing to increasing the integrated luminosity of the KEKB B-factory.
KEK, Ibaraki
UTNL, Ibaraki
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
AET Japan, Inc., Kawasaki-City
KEK, Ibaraki
IHI/Yokohama, Kanagawa
UTNL, Ibaraki
Akita National College of Technology, Akita
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
UTNL, Ibaraki
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
ISIR, Osaka
* J. Yang, T. Kondoh, K. Kan, T. Kozawa, Y. Yoshida and S. Tagawa: Nucl. Instrum. Methods Phys. Res., Sect. A 556 (2006) 52-56
ISIR, Osaka
AIST, Tsukuba, Ibaraki
RISE, Tokyo
KEK, Ibaraki
*M. Goldstein et al., Proc. of the 27th Int. FEL conference, Stanford, California, USA (2005) pp.422-425**A. Endo, Sematic EUV source workshop, Barcelona, Spain (2006)
ISIR, Osaka
ISIR, Osaka
RISE, Tokyo
KEK, Ibaraki
AIST, Tsukuba, Ibaraki
USTC/NSRL, Hefei, Anhui
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
An intense L-band electron accelerator is now being installed at PAL (Pohang Accelerator Laboratory) for initial tests. It is capable of producing 10-MeV electron beams with average 30 kW. This accelerator has a diode-type E-gun, a pre-buncher cavity, and an accelerating column with the built-in bunching section. We conduct simulational study for the commissioning scenario by the PARMELA code. At first, we observe the beam position and the beam current when the beam line is misaligned under no fields. Next, turning on focusing solenoids we observe the beam position change to check the alignments of the solenoids. Finally, varying RF power and phase of the pre-buncher we observe beam energy and beam power to obtain the optimum pre-buncher condition. In this paper, we present simulational results for each step. We also present commissioning strategies based on these results.
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
For a compact X-ray source, we designed a C-band standing-wave electron accelerator. It is capable of producing 4-MeV electron beams with 50-mA peak beam current. As an RF source, we use 5-GHz magnetron with duty factor of 0.08%. The accelerating structure is bi-periodic and on-axis coupled structure, operated with π/2-mode standing waves. Each cavity in the bunching and normal cell is designed by the MWS code and measured with aluminium prototype cavity. As per the dispersion relation derived from the measurement results, calibration factor obtained for the actual copper cavity.
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
An intense L-band electron accelerator is designed and under development for CESC (Cheorwon Electron-beam Service Center) irradiation applications. It is capable of producing 10-MeV electron beams with average 30 kW. For an RF source, a Thales klystron is used with 1.3 GHz, pulsed 25 MW, and average 60 kW. The accelerator column, fabricated by IHEP in China, is operated with 2π/3 mode traveling-wave under the fully-beam-loaded condition. The modulator was fabricated with inverter power supplies. The klystron was assembled to the klystron tank with pulse transformer. The high-voltage pulse test was conducted for the klystron tube. In this paper, we present design details of the accelerator and current status.
CERN, Geneva
Ankara University, Faculty of Sciences, Tandogan/Ankara
CERN, Geneva
IFIC, Valencia
CERN, Geneva
STFC/RAL, Chilton, Didcot, Oxon
Spoilers in the ILC Beam Delivery System are required to survive without failure a minimum of 1-2 direct impacts from each energetic electron or positron bunch of charged particles, in addition to maintaining low geometric and resistive wall wake fields. The transient shock wave resulting from rapid localised beam heating and its implications for spoiler design are studied using ANSYS. Shockwave propagation is modelled in 2 dimensions showing the effect of dilatational shockwaves striking free surfaces, producing reflected dilatational and distortional waves. The implication of these relflected waves on the damage of the collimators is also discussed.
Cockcroft Institute, Warrington, Cheshire
STFC/RAL, Chilton, Didcot, Oxon
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Liverpool University, Science Faculty, Liverpool
Durham University, Durham
ANL, Argonne, Illinois
SLAC, Menlo Park, California
Illinois Institute of Technology, Chicago, Illinois
A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator Facility (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. An imaging system is being put together to identify single emitters on the cathode surface. This will allow us to study dark current properties in the gun. We also plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV). Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after can shed some light on a modification of metal surface after the breakdown.
ANL, Argonne, Illinois
Illinois Institute of Technology, Chicago, Illinois
Metamaterials (MTM) are artificial periodic structures made of small elements and designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be described by a permittivity and permeability, just like natural materials. Metamaterials can be customized to have the permittivity and permeability desired for a particular application. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves, for example, can be produced in a LHM-loaded waveguide without corrugations. In this paper we present theoretical studies and computer modeling of waveguides loaded with 2D anisotropic metamaterials, including the dispersion relation for a MTM-loaded waveguide. The dispersion relation of a MTM-loaded waveguide has several interesting frequency bands which are described. It is shown theoretically that dipole mode suppression may be possible. Therefore, metamaterials can be used to suppress wakefields in accelerating structures.
ANL, Argonne, Illinois
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
SLAC, Menlo Park, California
Fermilab, Batavia, Illinois
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
Colliding laser pulses* have been proposed as a method for controlling injection of electrons into a laser wakefield accelerator (LWFA) and hence producing high quality relativistic electron beams with energy spread below 1% and normalized emittances below 1 micron. The original proposal relied on three coaxial pulsesI. One pulse excites a plasma wake, and a collinear pulse following behind it collides with a counterpropagating pulse forming a beat pattern that boosts background electrons into accelerating phase. A variation of this method uses only two laser pulses** which may be non-collinear. The first pulse drives the wake, and beating of the trailing edge of this pulse with the colliding pulse injects electrons. Non-collinear injection avoids optical elements on the electron beam path (avoiding emittance growth). We report on progress of non-collinear experiments at LBNL, using the Ti:Sapphire laser at the LOASIS facility of LBNL. Preliminary results indicate that electron beam properties are affected by the second beam. Details of the experiment will be presented.
* E. Esarey, et al, Phys. Rev. Lett 79, 2682 (1997).** G. Fubiani, Phys. Rev. E 70, 016402 (2004).
LBNL, Berkeley, California
OXFORDphysics, Oxford, Oxon
A GeV-class laser-driven plasma-based wakefield accelerator has been realized at the Lawrence Berkeley National Laboratory (LBNL). The device consists of a 100 TW-class high repetition rate Ti:sapphire LOASIS laser system of LBNL and a gas-filled capillary discharge waveguide developed at Oxford University. Results will be presented on the generation of GeV-class electron beams with a 3.3 cm long preformed plasma channel. The use of a discharge-based waveguide permitted operation at an order of magnitude lower density and 15 times longer distance than in previous experiments that relied on laser-preformed plasma channels. Laser pulses with peak power ranging from 10-50 TW were guided over more than 20 Rayleigh ranges and high-quality electron beams with energy up to 1 GeV were obtained. The dependence of the electron beam characteristics on plasma channel properties and laser parameters are discussed.
LBNL, Berkeley, California
At LBNL, laser wakefield accelerators (LWFA) now produce ultra-short electron bunches with energies up to 1 GeV[1]. As femtosecond electron bunches exit the plasma they radiate a strong burst in the terahertz range[2,3], via coherent transition radiation (CTR). Measuring the CTR properties allows non-invasive bunch-length diagnostics[4], a key to continuing rapid advance in LWFA technology. In addition, this method of CTR generation provides very high peak power that can lead novel THz-based applications. Experimental bunch length characterizations through electro-optic sampling as well as bolometric analysis are presented. Measurements demonstrate both the shot-by-shot stability of bunch parameters, and femtosecond synchronization between bunch, THz pulse, and laser beam.
[1] W. P. Leemans et al., Nature Physics 2, 696(2006)[2] W. P. Leemans et al., PRL 91, 074802(2003)[3] C. B. Schroeder et al., PRE 69, 016501(2004)[4] J. van Tilborg et al., PRL 96, 014801(2006)
LBNL, Berkeley, California
New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photoinjectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100 MHz CW, to provide beam bunches at a rate of one MegaHertz or more. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm2. The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for flat beam generation. Beam dynamics simulations indicate that normalized emittances on the order of 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10's of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.
LBNL, Berkeley, California
SLAC, Menlo Park, California
Electron cloud build-up and related beam instabilities are a serious concern for the positron damping ring of the International Linear Collider (ILC). To mitigate the effect use of grooved vacuum-chamber walls is being actively investigated in addition to more conventional techniques like surface coating, scrubbing, and/or conditioning. Experimental and simulation studies have characterized the effectiveness of the grooved surface by means of an effective secondary emission yield (SEY), which has been measured to be significantly lower than the SEY of a smooth surface of the same material. However, some inconsistencies of the results, and the need to model the experimental testing of the grooved surface concept in more detail, have motivated us to simulate the grooved surfaces directly. Specifically, we have augmented the code POSINST by adding the option to simulate the electron-cloud build-up in the presence of a grooved surface geometry. By computing the accumulated e-cloud density and comparing it with the same quantity computed for a smooth surface, we infer an effective SEY, and we thereby make contact with the effective SEY estimates obtained from previous studies.
MIT/PSFC, Cambridge, Massachusetts
A theory is presented for the design of an ideal non-relativistic circular beam system including a charged-particle emitting diode, a diode aperture, a circular beam tunnel, and a focusing magnetic field that matches the beam from the emitter to the beam tunnel. The magnetic field is determined by balancing the forces throughout the gun and transport sections of the beam system. OMNITRAK simulations are performed, validating theory. As applications, a circular electron beam system is discussed for space-charge-dominated beam experiments such as the University of Maryland Electron Ring (UMER), and a circular ion beam system is discussed for high energy density physics (HEDP) research.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne, Illinois
CLASSE, Ithaca
The ILC damping rings require wiggler magnets with large physical aperture and with excellent field quality to maintain the dynamic aperture of the rings. We consider two possible designs derived from the wigglers presently in operation at the Cornell Electron Storage Ring. Design optimization has been performed based on detailed tracking calculations of dynamic aperture and tune footprint in a full model of the damping ring. Results of finite-element modeling, transfer functions, and the accuracy of analytic models of the wiggler field will be discussed.
We are considering the implementation of a Lithium lens and SC solenoidal lens for collection of positrons in ILC undulator-based source. Such a lens installed right after the thin target, which is illuminated by gamma quants from helical undulator.
UCLA, Los Angeles, California
SLAC, Menlo Park, California
USC, Los Angeles, California
UCSB, Santa Barbara, California
Manhattan College, Riverdale, New York
The breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been measured. In this experiment at the Final Focus Test Beam (FFTB) facility, the 30 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 microns. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compression of the electron bunch. The onset of breakdown, as indicated by a bright discharge, was found to correlate to a surface field of about 4 GV/m. An analysis of the damage sustained to the beam-exposed fibers, and its correlation to field amplitude, is also reported.
LLNL, Livermore, California
As part of the ongoing development of fast neutron imaging technology for national secu-rity applications at LLNL, a large-format imaging optics system has been designed and built. The system will be used to acquire radiographic images of heavily-shielded low-Z objects irradiated by ~ 10 MeV neutrons and is expected to have an ultimate spatial resolution ~ 1 mm (FWHM). It is comprised of a 65 cm x 65 cm plastic scintillator (e.g. BC-408), an aluminized front-surface turning mirror and a fast (~ f/1.25) optical lens coupled to a CCD camera body with a cryo-cooled, back-illuminated 4096 x 4096 (15 micron) pixel sensor. The lens and camera were developed and purchased from vendors and system integration was done at LLNL. A description of the overall system and its initial performance characteristics shall be presented.
RadiaBeam, Los Angeles, California
UCLA, Los Angeles, California
The fixed-field alternating-gradient (FFAG) betatron has emerged as a viable alternative to RF linacs as a source of high-energy radiation for industrial and security applications. For industrial applications, high average currents at modest relativistic electron beam energies, typically in the 5 to 10 MeV range, are desired for medical product sterilization, food irradiation and materials processing. For security applications, high power x-rays in the 3 to 20 MeV range are needed for rapid screening of cargo containers and vehicles. In a FFAG betatron, high-power output is possible due to high duty factor and fast acceleration cycle: electrons are injected and accelerated in a quasi-CW mode while being confined and focused in the fixed-field alternating-gradient lattice. The beam is accelerated via magnetic induction from a betatron core made with modern low-loss magnetic materials. Here we present the design and status of a prototype FFAG betatron, called the Radiatron, as well as future prospects for these machines.
UCLA, Los Angeles, California
Euclid TechLabs, LLC, Solon, Ohio
LLNL, Livermore, California
Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerating structure as a source of THz coherent Cerenkov radiation. For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the device operates in a single-mode regime, producing narrow-band radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ~50 μJ radiated energy per pulse achievable using the electron beam currently in operation at the Neptune Advanced Accelerator Research Laboratory at UCLA (~13 MeV beam energy, ~200 μm RMS bunch length, ~500 pC bunch charge). Preparations underway for installation of the experiment are discussed.
INFN/LNF, Frascati (Roma)
INFN-Roma II, Roma
UCLA, Los Angeles, California
Jet Propulsion Laboratory, Pasadena, California
Instituto Superior Tecnico, Lisbon
UCLA, Los Angeles, California
The extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than that in current accelerators has been well documented. We develop a phenomenological framework for Laser Wakefield Acceleration (LWFA) in the 3D nonlinear regime, in which the plasma electrons are expelled by the radiation pressure of a short pulse laser, leading to nearly complete blowout. This theory provides a recipe for designing a LWFA for given laser and plasma parameters and estimates the number and the energy of the accelerated electrons whether self-injected or externally injected. These formulas apply for self-guided as well as externally guided pulses (e.g. by plasma channels). Based on this theory, we will present scenarios on how to build a single stage accelerator with output energies from GeV to TeV. Particle-In-Cell (PIC) simulations are used to verify our theory. This work was supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345.
UCLA, Los Angeles, California
High-intensity short-pulse laser guiding in plasma channels has extended the length over which acceleration occurs in laser wake field accelerators*. Recent multidimensional nonlinear plasma wave theory predicts a range of optimal characteristics for self-guiding of laser pulses in the blowout regime for pulses shorter than a plasma wavelength**. This theory predicts a robust, stable parameter space for self-guiding and wake production and has been verified through multidimensional particle-in-cell simulations. We experimentally explore the plasma dynamics and laser pulse propagation using a 50 fs multi-terawatt Ti:Sapphire laser in a helium plasma at plasma densities, laser powers, and spot sizes within this parameter space. Our parameters are in the range where the plasma is underdense and the laser power is much greater than the critical power for self focusing. The evolution of the laser pulse and plasma channel will be followed over several Rayleigh lengths.
* C. Geddes et. al., Nature (London) 431, 538 (2004)** W. Lu et. al., Phys. Plasmas 13, 056709 (2006)
UCLA, Los Angeles, California
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Euclid TechLabs, LLC, Solon, Ohio
USC, Los Angeles, California
LLNL, Livermore, California
Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC FFTB, are foreseen to be produced soon at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of >10 GV/m. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 μm and 200 μm ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in excess of 4 GV/m (2 GV/m accelerating field) in fused silica. With the construction and commissioning of the SABER facility at SLAC, new experiments are made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. The E169 collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures.
Instituto Superior Tecnico, Lisbon
UCLA, Los Angeles, California
The realization of high quality LWFA-produced electron beams requires laser pulses that remain focused for distances exceeding the Rayleigh length. It is often thought that a short pulse laser cannot be self-guided and some form of external optical guiding is needed. As short pulse lasers with higher power are rapidly coming online to test the LWFA concept it is vital to understand the nature of their propagation through centimeters of plasma. We argue that a degree of self-guiding is possible for short ultra-intense pulses that have been shown to lead to complete ponderomotive expulsion of plasma electrons. Furthermore, the generation of a high quality electron beam requires proper loading of the wake. We have developed a theoretical framework which predicts the maximum number of electrons which can be loaded in the wake, as well as the optimal charge density profile for beam loading. Using the PIC codes OSIRIS and QuickPIC we present designs of LWFA accelerators that verify our theoretical estimates as well as demonstrate the potential of LWFA to produce high energy electron beams with high beam quality.
USC, Los Angeles, California
UCLA, Los Angeles, California
Simulation and analysis of the ion motion and multiple ionization in a plasma wakefield accelerator is presented for the parameters required of a future ILC afterburner. We show that although ion motion leads to substantial emittance growth for extreme parameters of future colliders in the sub-micron spot size regime, several factors that can mitigate the effect are explored. These include sunchrotron damping, plasma density gradient and hot plasma.
USC, Los Angeles, California
STI, Washington
BNL, Upton, Long Island, New York
We investigate various plasma wakefield accelerator schemes that rely on multiple electron bunches to drive a large amplitude plasma wave, which are followed by a witness bunch at a phase where it will sample the high acceleration gradient and gain energy. Experimental verifications of various two bunch schemes are available in the literature; here we provide analytical calculations and numerical simulations of the wakefield dependency and the transformer ratio when M drive bunches and one witness bunch are fed into a high density plasma, where M is between 2 and 10. This is a favorable setup since the bunches can be adjusted such that the transformer ratio and the efficiency of the accelerator are enhanced compared to single bunch schemes. The possibility of a five bunch ILC afterburner to accelerate a witness bunch from 100 GeV to 500 GeV is also examined.
USC, Los Angeles, California
STI, Washington
BNL, Upton, Long Island, New York
Two ~100 fs electron bunches, separated in energy by approximately 1.8 MeV and in time by 0.5-1 ps, were sent through a capillary discharge plasma. The plasma density was varied from ~1·1014/cc to ~1·1017/cc. A 2-D PWFA model indicates the net wakefield produced by the bunches will depend on their relative charge, temporal separation, and the plasma density. This will affect the amount of energy gain or loss of the second bunch. During measurements of the energy spectrum of the second bunch, we observed a difference in the amount of gain or loss depending on the plasma density, which is consistent with the model prediction.
BNL, Upton, Long Island, New York
USC, Los Angeles, California
STI, Washington
The presentation will cover experimental results on generation and measurement of the beams with theμbunches length from 1 to 50 microns at Brookhaven Accelerator Test Facility. Arbitrary number of microbunches is sliced out of 5 ps long beam using wire mesh and slits. The details of beam structure are characterized using CSR interferometer and 6 mm long plasma wakefield channel with the controllable plasma density.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
A new approach for positron acceleration in non-linear plasma wakefields driven by electron beams is presented. Positrons can be produced by colliding an electron beam with a thin foil target embedded in the plasma. Integration of positron production and acceleration in one stage is realized by a single relativistic, intense electron beam. Simulations with the parameters of the proposed SABER facility at SLAC suggest that this concept could be tested there.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
Recent experiments at SLAC have shown that high gradient acceleration of electrons is achievable in meter scale plasmas. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch length and beam waist location were varied systematically at constant charge. Here we investigate the correlation of peak beam current to the decelerating gradient. Limits on the transformer ratio will also be discussed. The results are compared to simulation.
SLAC, Menlo Park, California
University of Oregon, Eugene, Oregon
KEK, Ibaraki
SLAC, Menlo Park, California
Emittance growth is an important issue for plasma wakefield accelerators (PWFAs). Multiple Coulomb scattering (MCS) is one factor that contributes to this growth. Here, the MCS emittance growth of an electron beam traveling through a PWFA in the blow out regime is calculated. The calculation uses well established formulas for angular scatter in a neutral vapor and then extends the range of Coulomb interaction to include the effects of traveling through an ion column. Emittance growth is negligible for low Z materials; however, becomes important for high Z materials.
SLAC, Menlo Park, California
DESY, Hamburg
Fermilab, Batavia, Illinois
UMAN, Manchester
Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes.
Stanford University, Stanford, Califormia
SLAC, Menlo Park, California
[1] 'International Linear Collider Reference Design Report', April 2007
[2] Y Nosochkov, A. Seryi, Phys. Rev. ST Accel. Beams 8, 021001 (2005)
[3] B. Parker, A. Seryi, Phys. Rev. ST Accel. Beams 8, 041001 (2005)
SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
The NLC Test Accelerator (NLCTA) at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun has been installed with diagnostics and a low energy spectrometer (LES) at 6 MeV together with a large-angle extraction line at 60 MeV. This is followed by a matching section, buncher and final focus for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range (2\%), high resolving power (104) spectrometer (HES) for electron bunch analysis. Emittance compensating solenoids and the LES are used to tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5° extraction line provide 1:1 phase space transfer without use of sextupoles for a large, 6D phase space volume and range of input conditions. Spot sizes of a few microns at the IP (or HES object) allow tests of microscale structures as well as high resolving power at the image of the HES. Tolerances, tuning sensitivities and diagnostics are discussed together with the latest commissioning results and their comparison to design expectations.
SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
The E163 laser acceleration experiments conducted at SLAC have stringent requirements on the temporal properties of two regeneratively amplified, 800nm, Spitfire laser systems. To determine the magnitude and cause of timing instabilities between the two Ti:Sapphire amplifiers, we pass the two beams through a cross-correlator and focus the combined beam onto a Hamamatsu G1117 photodiode. The photodiode has a bandgap such that single photon processes are suppressed and only the second order, two-photon process produces an observable response. The response is proportional to the square of the intensity. The diode is also useful as a diagnostic to determine the optimal configuration of the compression cavity.
Yoshihiro Takagi et al, 'Multiple- and Single-shot autocorrelator based on two-photon conductivity in semiconductors.' Optics Letters, Vol. 17, No. 9, May 1, 1992.
SLAC, Menlo Park, California
ANL, Argonne, Illinois
Undulator-based positron source is adopted as the International Linear Collider baseline design. Complete optics to transport the positron beam having large angular divergence and large energy spread from a thin Ti target to the entrance of the 5 GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the optical matching device, capture accelerator system, transport system, superconducting booster linac, spin rotators, and energy compressor. Positron capture efficiency of different schemes (immersed vs shielded target, and flux concentrator vs quarter wave transformation for the optics matching system) is compared. For the scheme of a shielded target and quarter wave transformation, the simulation shows that 15.1% of the positrons from the target are captured within the damping ring 6-D acceptance at the entrance of the damping ring injection line.
SLAC, Menlo Park, California
A train of 2-nsμbunches are generated in the DC-gun based injector in the ILC e- source; a bunching system with extremely high bunching efficiency to compress bunch down to 20 ps FWHM is designed. Complete optics to transport the electron beam to the 5-GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the bunching system, pre-acceleration, chicane, 5-GeV SC booster linac, spin rotators and energy compressor. It shows more than 95% of electrons from the DC-gun are captured within the 6-D damping ring acceptance at the entrance of damping ring injection line. The field and alignment errors, and orbit correction are analyzed.
Jefferson Lab, Newport News, Virginia
A new 100 kV GaAs DC Load Lock Photogun has been constructed at Jefferson Laboratory, with improvements for photocathode preparation and for operation in a high voltage, ultra-high vacuum environment. Although difficult to gauge directly, we believe that the new gun design has better vacuum conditions compared to the previous gun design, as evidenced by longer photocathode lifetime, that is, the amount of charge extracted before the quantum efficiency of the photocathode drops by 1/e of the initial value via the ion back-bombardment mechanism. Photocathode lifetime measurements at DC beam intensity of up to 10 mA have been performed to benchmark operation of the new gun and for fundamental studies of the use of GaAs photocathodes at high average current*. These measurements demonstrate photocathode lifetime longer than one million Coulombs per square centimeter at a beam intensity higher than 1 mA. The photogun has been reconfigured with a high polarization strained superlattice photocathode (GaAs/GaAsP) and a mode-locked Ti:Sapphire laser operating near band-gap. Photocathode lifetime measurements at beam intensity greater than 1 mA are measured and presented for comparison.
"Further Measurements of Photocathode Operational Lifetime at Beam Intensity >1mA using the CEBAF 100 kV DC GaAs Photogun", J. Grames et al., Proc. of the 17th Inter. Spin Symposium, Japan (2006).
Jefferson Lab, Newport News, Virginia
ODU, Norfolk, Virginia
A positron source for the 6 GeV (or the proposed 12 GeV upgrade) recirculating linacs at Jefferson Lab is presented. The proposed 100nA CW positron source has several unique characteristics; high incident beam power (100kW), 10 MeV incident electron beam energy, CW incident beam and CW production. Positron production with 10 MeV electrons has several advantages; the energy is below neutron threshold so the production target will not become activated during use and the absolute energy spread is bounded by the low incident energy. These advantages are offset by the large angular distribution of the outgoing positrons. Results of simulations of the positron production, capture, acceleration and injection into the recirculating linac are presented. Energy flow and thermal management of the production target present a challenge and are included in the simulations.
High power RF testing has been performed on a novel axisymmetric radiofrequency electron gun at a frequency of 11.43 GHz using the magnicon facility at the Naval Research Laboratory. This gun utilizes coaxial coupling from the upstream end of unit and allows for axisymmetric tuning of both the cathode cell and the second cell. The features of the gun have been proven to operate at high gradients. The overall design of the gun will be discussed along with the results of the high power RF testing.
UCLA, Los Angeles, California
*R. Yoder and J. Rosenzweig, Phys. Rev. STAB 8, 111301 (2005); Z. Zhang et al., Phys. Rev. STAB 8, 071302 (2005); A. Mizrahi and L. Schachter, Phys. Rev. E 70, 016505 (2004).
ANL, Argonne, Illinois
International Tomography Center, SB RAS, Novosibirsk
Saint-Petersburg State University, Saint-Petersburg
Euclid TechLabs, LLC, Solon, Ohio
Technion, Haifa
The PASER is a new method for particle acceleration, in which energy from an active medium is transferred to a charged particle beam. The effect is similar to the action of a maser or laser with the stimulated emission of radiation being produced by the virtual photons in the electromagnetic field of the beam. We are developing a demonstration PASER device operating at X-band, based on the availability of a new class of active materials that exhibit photoinduced electron spin polarization. We will report on the status of active material development and measurements, numerical simulations, and preparations for microwave PASER experiments at the Argonne Wakefield Accelerator facility.
Stanford University, Stanford, Califormia
SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
BNL, Upton, Long Island, New York
An electron cooler, based on an Energy Recovery Linac (ERL) is under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. In order to achieve sufficient cooling of the ion beams the electron have to have a charge of 5 nC and a normalized emittance less than 4 mm mrad. This paper presents the progress in optimizing the injector and the emittance improvements from shaping the charge distribution in the bunch.
BNL, Upton, Long Island, New York
Emittance compensation is a well established technique* for minimizing the emittance of electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincides the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in reference**. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating frame. We describe a method and tools for a compensation that includes the beam magnetization.
* L. Serafini, J. B. Rosenzweig, Phys. Rev E 55, 7565, (1997)
** X. Y. Chang, I. Ben-Zvi, J. Kewisch, Phys. Rev ST AB 9, 044201, (2006)
BNL, Upton, Long Island, New York
Acceleration of electrons up to 10 GeV for a future electron-ion collider eRHIC (Relativistic Heavy Ion Collider) could be performed with the energy recovery linac with multiple passes. An energy recovery scheme is required if a superconducting linac is used for acceleration. We report on an attempt to make a combination of a multi-pass linac with non-scaling Fixed Field Alternating Gradient (NS-FFAG) arcs. Two NS-FFAG arcs would allow electrons to pass through the same structure with different energies. The beam will be accelerated by the superconducting linac at the top of the sine function, and returned to the front of the linac by the non-scaling FFAG. This process is repeated until the total energy of 10 GeV is reached. After collisions the beam is brought back by the NS-FFAG and decelerated before being dumped.
BNL, Upton, Long Island, New York
Compton interaction point incorporated into a high-average-power laser cavity is the key element of the Polarized Positron Source (PPS) concept proposed for ILC [1]. According to this proposal, circularly polarized gamma rays are produced in Compton backscattering from a 6 GeV linac e-beam inside a CO2 laser amplifier cavity. Intra-cavity positioning of the interaction point allows multiple laser recycling to match the electron bunch train format. We conducted experimental tests of multi-pulse operation of such active Compton cavity upon injection of a picosecond CO2 laser beam. Together with earlier demonstration of a high x-ray yield via the e-beam/CO2-laser backscattering, these new results show a viability of the entire PPS concept and closely prototype the laser source requirements for ILC.
[1] V. Yakimenko and I. V. Pogorelsky, Phys. Rev. ST Accel. Beams 9, 091001 (2006)
ANL, Argonne, Illinois
Euclid TechLabs, LLC, Solon, Ohio
LET
SLAC, Menlo Park, California
A joint project is underway by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a compact X-band accelerator for testing dielectric-loaded accelerator (DLA) structures.* The accelerator will use a 5-MeV injector previously developed by the Tsinghua University in Beijing, China, and will accommodate test structures up to 0.5 m in length. Both the injector and the structures will be powered by an 11.4-GHz magnicon amplifier that can produce 25 MW, 200-ns output pulses at up to 10 Hz. The injector will require ~5 MW of rf power, leaving ~20 MW to power the test structures. This paper will present a progress report on the construction and commissioning of the test accelerator, which will be located in a concrete bunker in the Magnicon Facility at NRL.
* S. H. Gold et al., Proc. PAC 2005.
NRL, Washington, DC
CEA, Pontfaverger-Moronvilliers
[1] D. Einfeld, "Status of the ALBA project", EPAC 06, Scotland, Edinburgh, June 2006.[2] D. Tronc and A. Setty, "Electrons RF auto-focusing and capture in bunchers", Linear Accelerator Conference 1988, Virginia.
TU Darmstadt, Darmstadt
TEMF, Darmstadt
Beam dynamics simulations for computationally large problems are challenging tasks. On the one hand, to accurately simulate the electromagnetic field distribution within the whole device and the surrounding environment it is essential to consider all necessary device components including even small geometry details, complicated material distributions and the field excitations. On the other hand, further computational effort has to be put into precise modeling of the injected particle beam for detailed beam dynamics simulations. Under linear conditions, it is possible to separate the field calculation of the device from the computation of the particles self-field which can result in the proper application of diverse numerical schemes for the individual field contributions. In the paper it is demonstrated how the static electric and magnetic fields of a Wien filter beam line element can be treated as applied external fields within the beam dynamics simulation tool V-Code under the assumption that the interaction of the particle beam with the surrounding materials can be neglected.
DESY, Hamburg
Uni HH, Hamburg
Universita' degli Studi di Milano, Milano
INFN-Milano, Milano
INFN-Milano, Milano
Universita' degli Studi di Milano, Milano
KEK, Ibaraki
NIRS, Chiba-shi
Hokkaido University, Sapporo
TEMF, Darmstadt
Muroran Institute of Technology, Department of Electrical and Electronic Engineering, Muroran
JLAB, Newport News, Virginia
Jefferson Lab, Newport News, Virginia
PKU/IHIP, Beijing
We present work directed at examining the performance of various front end components of an ERL based light source. These include electron source, bunch compression, merger, and accelerating sections, with parameter space dictated by proposed facilities (at FSU and Beijing University). These facilities share enough common structural features to make the study applicable to both to a large extent. In this report we will discuss the 6D phase space evolution through the front end based on simulation, with reliable modeling of magnetic and superconducting RF fields. Discussion will be devoted to relative merits of alternative designs, robustness and operational scenarios.
TUB, Beijing
LBNL, Berkeley, California
LPI, Moscow
Cornell University, Department of Physics, Ithaca, New York
BINP SB RAS, Novosibirsk
IC SB RAS, Novosibrsk
ICM&MG SB RAS, Novosibirsk
MSU, Moscow
UPC, Barcelona
CERN, Geneva
The electrostatic Particle in Cell code 'Faktor2' is extended to 3D, and is parallelised. Results for electron cloud buildup in end regions of damping ring dipoles for next generation linear colliders are presented.
CERN, Geneva
GSI, Darmstadt
Fermilab, Batavia, Illinois
CERN, Geneva
BNL, Upton, Long Island, New York
GSI, Darmstadt
KEK, Ibaraki
SLAC, Menlo Park, California
LBNL, Berkeley, California
CESR-LEPP, Ithaca, New York
Alfred University, Alfred, New York
Presently, CESR is operated at two different beam energies, low energy (E=2GeV) for high energy physics (CESR-c), and high energy (E=5.3GeV) for synchrotron radiation production (CHESS). The electron and positron bunches vertical dynamics at these two energies are vastly different, in part due to the change in the pretzel orbit, the presence of wiggler magnets at low energy, and synchrotron radiation power at two vastly different energies. Using the 32 channel photomultiplier array*, we measured the vertical beam dynamics on a turn-by-turn basis during CHESS and CESR-c operation as well as dedicated machine studies time. For these studies we quantify the electron cloud effects such as vertical tune shift and vertical beam size blow-up along the electron and positron trains at these two vastly different beam energies. In addition, the turn-by-turn capability of the PMT array allows us to study the vertical bunch dynamics over 10k turns.
* Design and Implementation of an Electron and Positron Multibunch Turn-by-Turn Vertical Beam Profile Monitor in CESR-PAC2007 proceedings
ANL, Argonne, Illinois
Fermilab, Batavia, Illinois
A direct space-charge force model has been implemented in the tracking code elegant. The user can simulate transverse space-charge effects by inserting space-charge elements in the beamline at any desired position. Application to the International Linear Collider damping ring is presented in this paper. We simulated beam under equilibrium conditions, as well as the entire damping cycle from injection to extraction. Results show that beam halo is generated due to space charge effects. This would be a significant concern for the ILC damping ring and a detailed follow-up study is needed.
Fermilab, Batavia, Illinois
JINR, Dubna, Moscow Region
Presently the Fermilab Booster can accomodate about half the maximum proton beam intensity which the Linac can deliver. One of the limitations is related to large vertical tuneshift produced by space-charge forces at injection energy. In the present report we study the nonlinear beam dynamics in the presence of space charge and magnet imperfections and analyze the possibility of space charge compensation with electron lenses.
Fermilab, Batavia, Illinois
Estimates indicate that the electron cloud effect could be a limiting factor for Main Injector intensity upgrades, with or without a the presence of a new 8 GeV superconducting 8GeV Linac injector. The effect may turn out to be an issue of operational relevance for other parts of the Fermilab accelerator complex as well. To improve our understanding of the situation, two sections of specially made vacuum test pipe outfitted for electron cloud detection with ANL provided Retarding Field Analyzers (RFAs), were installed in the Tevatron and the Main Injector. In this report we present some measurements, compare them with simulations and discuss future plans for studies.
Fermilab, Batavia, Illinois
To assess the effects of the electron cloud on Main Injector intensity upgrades, simulations of the cloud buildup were carried out using POSINST and compared with ECLOUD. Results indicate that even assuming an optimistic 1.3 maximum secondary electron yield, the electron cloud remains a serious concern for the planned future operational of mode of 500 bunches, 3·1011 proton per bunch. Electron cloud buildup can be mitigated in various ways. We consider a plausible scenario involving solenoids in straight section and a single clearing strip electrode (like SNEG in Tevatron)held at a potential of 500V. Simulations with parameters corresponding to Tevatron and Main Injector operating conditions at locations where special electron cloud detectors have been installed have been carried out and are in satisfactory agreement with preliminary measurements.
UMD, College Park, Maryland
(*) Simulation of Longitudinally Modulated Electron Beams. C. P. Neuman and P. G. O'Shea. In 2006 Advanced Accelerator Concepts Workshop, AIP Conference Proceedings, 877, 621-627. Melville, AIP (2006).
UMD, College Park, Maryland
(*) Simulation of Longitudinally Modulated Electron Beams. C. P. Neuman and P. G. O'Shea. In 2006 Advanced Accelerator Concepts Workshop, AIP Conference Proceedings 877, edited by M. Conde and C. Eyberger, 621-627. Melville, NY, AIP (2006).
LBNL, Berkeley, California
CIPS, Boulder, Colorado
LBNL, Berkeley, California
Tech-X, Boulder, Colorado
Simulation studies are under way to analyze the dynamics of microwave transmission through a beam channel containing electron clouds. Such an interaction is expected to produce a shift in phase accompanied by attenuation in the amplitude of the microwave radiation. Experimental observation of these phenomena would lead to a useful diagnosis tool for electron clouds. This technique has already been studied* at the CERN SPS. Similar experiments are being proposed at the PEP-II LER at SLAC as well as the Fermilab MI. In this study, simulation results will be presented for a number of cases including those representative of the above mentioned experiments. The code VORPAL is being utilized to perform electromagnetic particle-in-cell (PIC) calculations. The results are expected to provide guidance to the above mentioned experiments as well as lead to a better understanding of the problem.
* T. Kroyer, F. Caspers, E. Mahner , pg 2212 Proc. PAC 2005, Knoxville, TN
IUCF, Bloomington, Indiana
We present a multislice approach for modeling the space-charge fields of bunched electron beams that are emitted from a metallic cathode using electromagnetic Green's function techniques. The multislice approach approximates a local region of the beam density and current with a slice of zero longitudinal thickness. We show examples of how the multislice approach can be used to accurately compute the space-charge fields for electron bunch lengths in the regime of photocathode sources, i.e. (<10 ps).
IUCF, Bloomington, Indiana
We demonstrate the computational requirements for a Green's function based photocathode simulation code called IRPSS. In particular, we show the necessary conditions, e.g. eigenmode number and integration time-step, for accurately computing the space-charge fields in IRPSS to less than 1 % error. We also illustrate how numerical filtering methods can be applied to IRPSS in conjunction with a multislice approach, for dramatically improving computational efficiency of electromagnetic field calculations.
ORNL, Oak Ridge, Tennessee
IUCF, Bloomington, Indiana
LANL, Los Alamos, New Mexico
We present ORBIT code simulations to examine the sensitivity of electron cloud properties to different proton beam profiles and to reproduce experimental results from the proton storage ring at Los Alamos National Laboratory. We study the recovery of electron clouds after sweeping, and also the characteristics of two types of electrons signals (prompt and swept) as functions of beam charge. The prompt signal means the peak height of electron sweeper signal before high voltage pulse applied on its electrode and after beam accumulation, and the swept signal means the spike height of electron sweeper signal during the high voltage pulse. To concentrate on the electron cloud dynamics, we use a cold proton bunch to generate primary electrons and electromagnetic field for electron dynamics. However, the protons receive no feedback from the electron cloud. Our simulations indicate that the proton loss rate in the field-free straight section might be an exponential function of proton beam charge and may also be lower than the averaged proton loss rate in a whole ring.
BNL, Upton, Long Island, New York
Tech-X, Boulder, Colorado
The design of the high-energy cooler for the Relativistic Heavy Ion Collider (RHIC) recently adopted a non-magnetized approach. To prevent recombination between the fully stripped gold ions and co-propagating electrons, a helical undulator magnet has been proposed. In addition, to counteract space-charge defocusing, weak solenoids are proposed every 10m. To understand the effect of these magnets on the cooling rate, numerical models of cooling in the presence of external fields are needed. We present an approach from first principles using the VORPAL parallel simulation code. We solve the n-body problem by exact calculation of pair-wise collisions. Simulations of the proposed RHIC cooler are discussed, including fringe field and finite interaction time effects.
BNL, Upton, Long Island, New York
Tech-X, Boulder, Colorado
The work at Tech-X Corp. is supported by the U. S. Department of Energy under a Phase I SBIR grant.
MIT/PSFC, Cambridge, Massachusetts
A warm-fluid theory of a thermal equilibrium for a rotating charged particle beam in a periodic solenoidal focusing magnetic field is presented. The warm-fluid equilibrium equations are solved in the paraxial approximation. It is shown that the flow velocity for the thermal equilibrium corresponds to periodic rigid rotation and radial pulsation. The equation of state for the thermal equilibrium is adiabatic. The beam envelope equation and self-consistent Poisson's equation are derived. The numerical algorithm for solving self-consistent Poisson's equation is discussed. Density profiles are calculated numerically for high-intensity beams. Temperature effects in such beams are investigated, and the validity of the warm-fluid theory is discussed. Examples of electron and ion beams are presented for space-charge-dominated beam and high energy density physics (HEDP) research.
UMD, College Park, Maryland
LLNL, Livermore, California
LBNL, Berkeley, California
One of the areas fundamental beam physics that serve as the rationale for recent research on UMER is the study of generation and evolution of beam halos. This physics can be accessed on a scaled basis in UMER at a small fraction of the cost of similar experiments on a much larger machine. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a potentially significant source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam in the vicinity of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo. Both experimental data and simulations will be presented to illustrate the details of this mechanism for halo formation.
UMD, College Park, Maryland
This is a numerical study of the effects of skew quadrupoles on the beam used in University of Maryland Electron Ring (UMER). As this beam is space-charge dominated, we expect new phenomena to be present compared to the emittance-dominated case. In our studies we find that skew quadrupoles can severely affect the halo of the beam and cause emittance growth, even in the first turn of the beam. For our simulations we used the WARP particle-in-cell code and we compared the results with the experimental study of skew quadrupole effects (to be reported separately).
UMD, College Park, Maryland
The University of Maryland Electron Ring (UMER) is a scaled model to investigate the transverse and longitudinal physics of space charge dominated beams. It uses a 10-keV electron beam along with other scaled beam parameters that model the larger machines but at a lower cost. Understanding collective behavior of intense, charged particle beams due to their space charge effects is crucial for advanced accelerator research and applications. This paper presents the experimental study of longitudinal dynamics of an initial density modulation on a spacecharge dominated beam. A novel experimental technique of producing a perturbation using a laser is discussed. Using a laser to produce a perturbation provides the ability to launch a pure density modulation and to have better control over the amount of perturbation introduced. Collective effects like space charge waves and its propagation over long distances in a quadrupole channel are studied. One dimensional cold fluid model is used for theoretical analysis and simulations are carried out in WARP-RZ.
UMD, College Park, Maryland
Longitudinal perturbations can be generated in the space-charge dominated regimes in which most beams of interest are born. To study the modification of transverse beam distributions by longitudinal beam dynamics, we have conducted experimental studies using low energy electron beams by taking time resolved images of a beam with longitudinal density perturbations. Two different diagnostics are used: optical transition radiation (OTR) produced from an intercepting silicon based aluminum screen and a fast (<5ns decay time) phosphor screen. It is found that the beam is significantly affected by the perturbation. However the OTR signal is very weak and requires over 45 minutes of frame integration. The fast phosphor screen has much better sensitivity (~1'000 times enhancement). In this paper, we also report on the time resolved measurement of a parabolic beam, showing interesting correlations between transverse and longitudinal distributions of the beam.
UMD, College Park, Maryland
This paper describes the longitudinal expansion of a 10 keV, 100 mA electron beam in the University of Maryland Electron Ring. The expansion of the beam tail was found to be sensitive to the choice of transverse focusing settings due to the presence of an abnormality in the beam current profile. Expansion of the beam head, where no abnormality was observed, is in good agreement with the one-dimensional cold fluid model.
STAR, Inc., Mequon, Wisconsin
SAIC, Burlington, Massachusetts
Particle orbit errors in multipacting and dark current computations can arise from inadequate field representation, poor surface modeling, and from the integration algorithm used to advance the particles. Established fields-based adaptive mesh refinement (AMR) methods *,** selectively improve the field and surface representation over several iterations in finite-element codes but they are not optimized for particle tracking. In particular, field emission and secondary emission models require precise surface representations and highly accurate field representations near surfaces, and these requirements are not adequately addressed in standard AMR techniques. In this paper we report on extensions to existing AMR support in the Analyst software package for particle tracking, including adaptive improvement of near-surface and on-surface field representations, and control of element aspect ratios throughout successive iterations. We also discuss the merits of automated identification of important regions of the mesh based on field levels and orbit estimation to guide AMR in multipacting calculations, and multipacting results for a SRF cavity will be presented.
* G. Drago, et al., IEEE Trans. on Mag., 28, 1992, pp. 1743-1746.** D. K. Sun, et al., IEEE Trans. on Mag., 36, July 2000, pp. 1596-1599.
LLNL, Livermore, California
LBNL, Berkeley, California
UMD, College Park, Maryland
Contamination from electrons is a concern for solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons, produced directly by beam ions hitting lattice elements or indirectly by ionization of desorbed neutral gas, can potentially alter the beam dynamics, leading to a time-varying focal spot, increased emittance, halo, and possibly electron-ion instabilities. The electrostatic particle-in-cell code WARP is used to simulate electron-cloud studies on the solenoid-transport experiment (STX) at Lawrence Berkeley National Laboratory. We present self-consistent simulations of several STX configurations to show the evolution of the electron and ion-beam distributions first in idealized 2-D solenoid fields and then in the 3-D field values obtained from probes. Comparisons are made with experimental data, and several techniques to mitigate electron effects are demonstrated numerically.
UCLA, Los Angeles, California
UCLA, Los Angeles, California
USC, Los Angeles, California
We proposed a novel algorithm, which uses pipelining to reduce the simulation time for beam-electron cloud interaction. In the pipelining algorithm the processors are divided into subgroups, and during the simulation different groups will be on consecutive time steps. The pipelining algorithm is applied to the fully parallelized Particle-In-Cell (PIC) code QuickPIC to overcome the limit of the number of processors that can be used at each time step. With the new algorithm, the accuracy of the simulation is preserved; and the speed of the simulation is improved by a factor proportional to the number of processors available. The long term beam evolution results for the CERN-LHC and the FNAL main injector are presented using the QuickPIC with pipelining algorithm.
SLAC, Menlo Park, California
LBNL, Berkeley, California
* J. Qiang et al, Phys. Rev. ST Accel. Beams 9,044204 (2006).
A novel 3D method of sheet beam (SB) gun design has recently been developed. Second order ruled surfaces (SORS) to define the geometry of the gun electrodes. The gun design process is made simpler if SORS are derived from simple analytical formulas. The coefficients of the mathematical expression are parameters that set the gun optic. A proposed design method is discussed and illustrated.
We present the features of CMAD, a newly developed self-consistent code which simulates both the electron cloud build-up and related beam instabilities. By means of parallel (Message Passing Interface - MPI) computation, the code tracks the beam in an existing (MAD-type) lattice and continuously resolve the interaction between the beam and the cloud at each element location, with different cloud distributions at each magnet location. CMAD simulates single-and coupled-bunch instability, allows tune shift, dynamic aperture and frequency map analysis and the determination of the secondary electron yield instability threshold. Preliminary results are presented.
In this study, we analyze the longitudinal effective CSR force for an energy-chirped Gaussian bunch moving relativistically on a circular orbit. With the geometry of the bunch tilt in dispersive regions (as induced by the initial energy-chirp) included in the retardation relation, the longitudinal effective CSR force thus calculated displays a variety of behaviors depending on the level of bunch compression. The variety ranges from the suppression of the longitudinal CSR force, for an undercompressed thin bunch, to an enhancement of the CSR interaction above that for a projected bunch, in a duration of path length shortly after the bunch crosses over the full compression point. The amplitude and duration of the enhancement depends on the bunch and lattice parameters. During this enhancement, the longitudinal effective CSR force depends sensitively on the particle's transverse position in the bunch. The physical picture of this phenomenon will be discussed.
PPPL, Princeton, New Jersey
LBNL, Berkeley, California
Plasmas are sources of electrons for charge neutralizing ion beams to allow them to focus to small spot sizes and compress their axial pulse length. Sources must operate at low pressures and without strong electric/magnetic fields. To produce meter-long plasmas, sources based on ferroelectric ceramics with large dielectric coefficients were developed. The sources use BaTiO3 ceramic to form plasma. The drift tube inner wall of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic and ~7 kV is applied across the wall of the ceramics. A 20-cm-long prototype source produced plasma densities of 5·1011 cm-3. It was integrated into the Neutralized Transport Experiment and successfully neutralized the K+ beam. A one-meter-long source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma over the length of the source in the 1·1010 cm-3 range. This source was integrated into NDCX for beam compression experiments. Experiments with this source yielded compression ratios ~80. Future work will consider longer and higher plasma density sources to support beam compression and high energy density experiments.
PPPL, Princeton, New Jersey
Evaluation of ion-atom charge-changing cross sections is needed for many accelerator applications. The validity of the classical trajectory approximation has been studied by comparing the results of simulations with available experimental data and full quantum-mechanical calculations [1]. Additionally, a theoretical criterion has been developed for the validity of the classical trajectory approximation [2]. For benchmarking purposes, a Classical Trajectory Monte Carlo simulation (CTMC) is used to calculate ionization and charge exchange cross sections for most simple, hydrogen and helium targets in collisions with various ions. The calculated cross sections compare favorably with the experimental results for projectile velocities near the projectile velocity corresponding to the maximum of cross section as a function of projectile velocity. At higher or lower velocities, quantum-mechanical effects become more significant and the CTMC results agree less well with the experimental values of the cross sections.
[1] I. D. Kaganovich, et al., , New Journal of Physics 8, 278 (2006).
[2] Igor D. Kaganovich, et al., Nucl. Instr. and Methods A 544, 91(2005).
DULY Research Inc., Rancho Palos Verdes, California
One of the most important targets for building modern particle accelerators is to increase the beam brightness. The purposes of building a dc/rf gun are to seek high bunch charge and low beam transverse emittance, two key parameters for enhancing brightness of accelerators. We present simulation results of the beam emittance changes in a dc/rf gun under different gun voltages. SUPERFISH and PARMELA were used to simulate the beam dynamics in the gun. These simulations indicate that a small beam transverse emittance (< 0.5 mm.mrad) can be obtained when the voltage on the dc gap is lower than 200 kV and the bunch charge is 200 pc, and increments of dc gap voltages will greatly improve the emittances.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
JINR, Dubna, Moscow Region
The traditional electron cooling system used in low-energy coolers employs an electron beam immersed in a longitudinal magnetic field. In the first relativistic cooler, which was recently commissioned at Fermilab, the friction force is dominated by the non-magnetized collisions between electrons and antiprotons. The design of the higher-energy cooler for Relativistic Heavy Ion Collider (RHIC) recently adopted a non-magnetized approach which requires a low temperature electron beam. However, to avoid significant loss of heavy ions due to recombination with electrons in the cooling section, the temperature of the electron beam should be very high. These two contradictory requirements are satisfied in the design of the RHIC cooler with the help of the undulator fields. The model of the friction force in the presence of an undulator field was benchmarked vs direct numerical simulations with an excellent agreement. Simulations of ion beam dynamics in the presence of such a cooler and helical undulator is discussed in detail, including recombination suppression and resulting luminosities.
BNL, Upton, Long Island, New York
JINR, Dubna, Moscow Region
The low-energy electron cooling system is based on an electron beam immersed in a longitudinal magnetic field of a solenoid. The coupling of the horizontal and vertical motion allows representation of the friction force as a sum of the transverse and longitudinal components. The analytic treatment proceeds by allowing several approximations, for example, uniform transverse density distribution of electron beam and Maxwellian distribution in the velocity space. The high-energy electron cooling system for RHIC is unique compared to standard coolers. It requires bunched electron beam. Electron bunches are produced by an Energy Recovery Linac (ERL), and cooling is planned without a longitudinal magnetic field. To address the unique features of the RHIC cooler, a generalized 3-D treatment of the cooling force was introduced in the BETACOOL code which allows to calculate the friction force from an arbitrary six-dimensional distribution of the electrons. Results based on this treatment are compared to typical approximations. Simulations for the RHIC cooler based on a realistic electron distribution from the ERL are presented.
BNL, Upton, Long Island, New York
An R&D facility for an Energy Recovery Linac (ERL) intended as part of the 'Electron-Cooling Xperiment' for RHIC is being constructed at this laboratory. The center piece of the project is the experimental 5-cell 703.75 MHz superconducting ECX cavity. Successful operation will depend on effective HOM suppression, and it is planned to achieve HOM damping exclusively with room temperature ferrite absorbers. A ferrite-lined pillbox model with dimensions reflecting the operational unit was assembled, and the cavity resonances and quality factors were determined from scattering coefficient measurements and were interpreted as surface impedance. Results from a 5-cell copper cavity with an attached ferrite absorber prototype are used for the prediction of the ECX cavity HOM damping. A rotational symmetric ferrite-lined pillbox was analyzed theoretically and compared with the simulation codesμWave Studio, GdfidL, and Superfish. Discrepancies of the resonance frequencies and Q-values were found, and steps to reach agreement are discussed.
BNL, Upton, Long Island, New York
Non-magnetized electron cooling of RHIC requires an electron beam energy of 54.3 MeV, electron charge per bunch of 5 nC, normalized rms beam emittance of 4 mm-mrad, and rms energy spread of 3·10-4 *. In this paper we describe a lattice of a two-pass SCRF energy recovery linac (ERL) and results of a PARMELA simulation that provides electron beam parameters satisfying RHIC electron cooling requirements.
* A. Fedotov, Electron Cooling Studies for RHIC II http://www.bnl.gov/cad/ecooling/docs/PDF/Electron_Cooling.pdf
BNL, Upton, Long Island, New York
A super-conducting RF R&D Energy recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL). This ERL will be used as a test facility to study issues relevant to high-current, high-brightness beams. One of the goals is to demonstrate an electron beam with high charge per bunch (~ 5 nC) and extremely low normalized emittance (~ 5 mm-mrad) at an energy of 20 MeV. In contrast with operational high-brightness linear electron accelerators, all presently operating ERLs have an order of magnitude larger emittances for the same charge per bunch. One reason for this emittance growth is that the merger system mixes transverse and longitudinal degrees of freedom, and consequently violates emittance compensation conditions. A merger system based on zigzag scheme* resolves this problem. In this paper we discuss performance of the present design of the BNL R&D ERL injector with a zigzag merger.
* V. N. Litvinenko, R. Hajima, and D. Kayran, Nucl. Instr. and Meth. A 557 (2006) 165.
BNL, Upton, Long Island, New York
Electron cooling at RHIC-II upgrade imposes strict requirements on the quality of the electron beam at the cooling section. Beam current dependent effects such as the space charge, wake fields, CSR in bending magnets, trapped ions, etc., will tend to spoil the beam quality and decrease the cooling efficiency. In this paper, we estimate the defocusing effect of the space charge at the cooling section and describe our plan to compensate the defocusing space charge force by focusing solenoids. We also estimate the energy spread and emittance growth cased by wake fields. Finally, we discuss ion trapping in the electron cooler and consider different techniques to minimize the effect of ion trapping.
BNL, Upton, Long Island, New York
Jefferson Lab, Newport News, Virginia
BNL, Upton, Long Island, New York
BNL, Upton, Long Island, New York
An Electron Beam Ion Source (EBIS), capable of producing high charge states and high beam currents of any heavy ion species in short pulses, is ideally suited for injection into a synchrotron. An EBIS-based, high current, heavy ion preinjector is now being built at Brookhaven to provide increased capabilities for the Relativistic Heavy Ion Collider (RHIC), and the NASA Space Radiation Laboratory (NSRL). Benefits of the new preinjector include the ability to produce ions of any species, fast switching between species to serve the simultaneous needs of multiple programs, and lower operating and maintenance costs. A state-of-the-art EBIS, operating with an electron beam current of up to 10 A, and producing multi-milliamperes of high charge state heavy ions, has been developed at Brookhaven, and has been operating very successfully on a test bench for several years. The present performance of this high-current EBIS will be presented, along with details of the design of the scaled-up EBIS for RHIC, and the status of its construction. Other aspects of the project, including design and construction of the heavy ion RFQ, Linac, and matching beamlines, will also be mentioned.
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
Next-generation heavy-ion beam accelerators require a great variety of high charge state ion beams (from protons to uranium) with up to an order of magnitude higher intensity than demonstrated with conventional Electron Cyclotron Resonance (ECR) ion sources. Optimization of the ion beam production for each element is therefore required. Efficient loading of the material into the ECR plasma is one of the key elements for optimizing the ion beam production. High-fidelity simulations provide a means to understanding where along the interior walls the uncaptured metal atoms are deposited and, hence, how to optimize loading of the metal into the ECR plasma. We are currently extending the plasma simulation framework VORPAL with models to investigate effective loading of heavy metals into ECR ion sources via alternate mechanisms, including vapor loading, ion sputtering and laser ablation. Here we will present the models, simulation results of vapor loading and initial comparisons with experiments at the VENUS source at LBNL.
MIT, Cambridge, Massachusetts
TUHH, Hamburg
DESY, Hamburg
The ILC Linac Group at SLAC is actively pursuing a broad range of R&D to improve the reliability and reduce the cost of the L-band (1.3 GHz) rf system and normal-conducting accelerators. Current activities include the development of a Marx-style modulator and a 10 MW sheet-beam klystron, operation of an L-band (1.3 GHz) rf source using an SNS HVCM modulator and commercial klystron, construction of an rf distribution system with adjustable power tap-offs and custom hybrids, tests of cavity coupler components to understand rf processing limitations, simulation of multipacting in the couplers, optimization of the cavity fill parameters for operation with a large spread in sustainable cavity gradients and operation of a 5-cell prototype positron capture cavity. This paper surveys the results from the past year and reviews L-band R&D at other labs, in particular, that at DESY for the XFEL project.
Ankara University, Faculty of Sciences, Tandogan/Ankara
CERN, Geneva
UU/ISV, Uppsala
Ankara University, Faculty of Engineering, Tandogan, Ankara
ASP, Clayton, Victoria
Melbourne
TEMF, Darmstadt
The computation of wake fields excited by ultra short electron bunches in accelerator components with geometrical discontinuities is a challenging problem, as an accurate resolution for both the small bunch and the large model geometry are needed. Several computational codes (PBCI, ROCOCO, CST PARTICLE STUDIO etc.) have been developed to deal with this type of problems. Wake field simulations of the RF electron gun of the Photoinjector Test Facility at DESY Zeuthen (PITZ) are performed whith different specialized codes. Here we present a comparison of the wake potentials calculated numerically obtained from the different codes. Several structures of the photoinjector are considered.
DESY, Hamburg
DESY Zeuthen, Zeuthen
FZK, Karlsruhe
* http://www.i-tech.si
INFN/LNF, Frascati (Roma)
DESY Zeuthen, Zeuthen
LAL, Orsay
YerPhI, Yerevan
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
BESSY GmbH, Berlin
KhNU, Kharkov
The Photo-Injector Test Facility at DESY in Zeuthen (PITZ) is an electron accelerator which was built to develop and optimize high brightness electron sources suitable for SASE FEL operation. Currently, in parallel to the operation of the existing setup, a large extension of the facility and its research program is ongoing. The beam line which has a present length of about 13 meters will be extended up to about 21 meters within the next two years. Many additional diagnostics components will be added to the present layout. Two high-energy dispersive arms, an RF deflecting cavity and a phase space tomography module will extend the existing diagnostic system of the photo injector and will contribute to the full characterization of new electron sources. We will report on the latest developments of the beam diagnostics at PITZ.
ELETTRA, Basovizza, Trieste
INFN/LNF, Frascati (Roma)
INFN-Roma II, Roma
Uni HH, Hamburg
DESY, Hamburg
Universita di Roma II Tor Vergata, Roma
The characterization of the transverse phase space for high charge density and high energy electron beams is a fundamental requirement in many particle accelerator facilities, since knowledge of the characteristics of the accelerated beams is of great importance for the successful development of the next generation light sources and linear colliders. The development of suitable beam diagnostics, non-invasive and non-intercepting, is therefore necessary to measure the properties of such beams. Optical Diffraction Radiation (ODR) is considered the most promise candidate, as testified by the interest of many laboratories all around the world. An experiment based on the detection of ODR has been set up at DESY FLASH Facility to measure the electron beam transverse parameters. The radiation is emitted by a 700 MeV-energy electron beam passing through a slit of 0.5 mm or 1 mm aperture depending on the beam size. The slit is opened by chemical etching on a screen made of aluminum deposited on a silicon substrate. Radiation is then detected by a air-cooled high sensitivity CCD camera. The status of the experiment and preliminary results are reported.
KEK, Ibaraki
CERN, Geneva
POSTECH, Pohang, Kyungbuk
KEK, Ibaraki
KEK, Ibaraki
* Y. Suetsugu et al., NIM-PR-A, Vol.556 (2006) 399.
RLNR, Tokyo
UTNL, Ibaraki
KURRI, Osaka
Central Research Institute of Electric Power Industry, Komae
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
KEK, Ibaraki
TUB, Beijing
* Dao Xiang and Wen-Hui Huang, Nucl. Instr. and Meth. in Phys. Res. B, 254 (2007) 165.** Dao Xiang and Wen-Hui Huang, Nucl. Instr. and Meth. in Phys. Res. A, 570 (2007) 357.*** Dao Xiang and Wen-Hui Huang, Phys. Rev. ST-AB, 10 (2007) 012801.
USTC/NSRL, Hefei, Anhui
A simple measurement method of beam bunch length in time domain for HLS (Hefei Light Source) has been proposed. The Bunch length measurement system is composed of an optical system, a high speed photo-receiver and a wide bandwidth oscilloscope. The photo-receiver which is made by FEMTO has high sensitivity and high bandwidth, which converts the synchrotron radiation light into electronic signal. The oscilloscope which is made by Tektronix is TDS7704B, which has a high bandwidth up to 7GHz and show the bunch length in time domain. The measurement results of the bunch length and its analysis are given. We compare the results with that determined by the conventional method using a streak camera.
CAEP, Mainyang, Sichuan
Fermilab, Batavia, Illinois
OTR interferometry (OTRI) is an attractive diagnostic for investigation of relativistic electron beam parameters. The diagnostic is currently under development at the A0 Photoinjector. This diagnostic is applicable for NML accelerator test facility that will be built at Fermilab. The experimental setups of the OTR interferometers for the Photoinjector prototype are described in the report. Results of simulations and measurements are presented and discussed.
CERN, Geneva
CERN, Geneva
NSRRC, Hsinchu
DESY, Hamburg
Royal Holloway, University of London, Surrey
BESSY GmbH, Berlin
The current PETRA II Laser-Wire system, being developed for the ILC and PETRA III, uses a piezo-driven mirror to scan laser light across an electron bunch. This paper reports on the recently installed electron-beam finding system, presenting recent horizontal and vertical profile scans with corresponding studies.
ANL, Argonne, Illinois
SLAC, Menlo Park, California
The Linac Coherent Light Source (LCLS), currently under design, requires accurate alignment between the electron beam and the undulator magnetic centerline. A Beam Finder Wire (BFW) instrument has been developed to provide beam location information that is used to move the undulators to their appropriate positions. A BFW instrument is mounted at each of the 33 magnets in the undulator section. Beam detection is achieved by electrons impacting two carbon fiber wires and then sensing the downstream radiation. The wires are mounted vertically and horizontally on a wire card similar to that of a traditional wire scanner instrument. The development of the BFW presents several design challenges due to the need for high accuracy of the wires' location and the need for removal of the wires during actual operation of the LCLS (30 microns repeatability is required for the wire locations). In this paper, we present the technical specification, design criteria, mechanical design, and results from prototype tests for the BFW.
ANL, Argonne, Illinois
In the IPNS RCS, a single proton bunch (h=1) is accelerated from 50 MeV to 450 MeV in 14.2 ms. The bunch experiences an instability shortly after injection (<1 ms). During the first 1 ms, the beam is bunched but little acceleration takes place; thus, this period of operation is similar to that of a storage ring. Natural vertical oscillations (assumed to be tune lines) show the vertical tune to be rising toward the bare tune value, suggesting neutralization of space charge and a reduction of its detuning effects. Neutralization time near injection ranges from 0.25 ms - 0.5 ms, depending on the background gas pressure. Oscillations move from the LSB to the USB before disappearing. Measurements made with a recently installed pinger system show the horizontal chromaticity to be positive early but approaching zero later in the cycle. The vertical chromaticity is negative throughout the cycle. During pinger studies, two lines are observed, suggesting the formation of islands. Neutralization of the beam space charge implies the generation of plasma in the beam volume early in the cycle which may then dissipate as the time-varying electric fields of the beam become stronger.
Jefferson Lab, Newport News, Virginia
PKU/IHIP, Beijing
We have evaluated the feasibility of using the optical diffraction radiation (ODR) generated as a 1- to 6-GeV CW electron beam passes nearby the edge of a single metal conducting plane as a nonintercepting (NI) relative beam size monitor for CEBAF. Previous experiments were successfully done using near-field imaging on the lower-current, 7-GeV beam at APS, and an analytical model was developed for near-field imaging. Calculations from this model indicate sufficient beam-size sensitivity in the ODR profiles for beam sizes in the 30-50 micron regime as found in the transport lines of CEBAF before the experimental targets. With anticipated beam currents of 100 microamps, the ODR signal from the charge integrated over the video field time should be ~500 times larger than in the APS case. These signal strengths will allow a series of experiments to be done on beam energy dependencies, impact parameters, polarization effects, and wavelength effects that should further elucidate the working regime of this technique and test the model. Plans for the diagnostics station that will also provide reference optical transition radiation (OTR) images will also be described.
ANL, Argonne, Illinois
Bunch purity is an important source quality factor for the magnetic resonance experiments at the Advanced Photon Source. Conventional bunch-purity monitors utilizing time-to-amplitude converters are subject to dead time. We present a novel design based on a single field-programmable gate array (FPGA) that continuously processes pulses at the full speed of the detector and front-end electronics. The FPGA provides 7778 single-channel analyzers (six per RF bucket). The starting time and width of each single-channel analyzer window can be set to a resolution of 178 ps. A detector pulse arriving inside the window of a single-channel analyzer is recorded in an associated 32-bit counter. The analyzer makes no contribution to the system dead time. Two channels for each RF bucket count pulses originating from the electrons in the bucket. The other four channels on the early and late side of the bucket provide estimates of the background. A single-chip microcontroller attached to the FPGA acts as an EPICS IOC to make the information in the FPGA available to the EPICS clients.
ANL, Argonne, Illinois
NSWC, West Bethesda, Maryland
Interest in nonintercepting (NI) beam size monitoring for top-up operations at the Advanced Photon Source (APS) motivated our investigations of optical diffraction radiation (ODR) techniques. We have reported our experiment results earlier. In particular, we wanted to monitor the beam size in the booster-to-storage ring (BTS) transport line using near-field ODR. An analytical model was numerically evaluated for the APS BTS beam size cases. In addition, the simulations show that near-field ODR profiles have sensitivity to beam size in the 20- to 50-μm region, which are relevant to X-ray FELs and the international linear collider (ILC). The simulation indicates that the orthogonal polarization component is close to a Gaussian distribution and more sensitive to beam size variations, and therefore is more suitable for beam size measurement. Under some circumstances the parallel polarization component shows a non-Gaussian distribution that is also beam size dependent. This report describes the simulation method, the results, and the comparison with experiment results.
SLAC, Menlo Park, California
Pavilion Technologies, Inc, Austin, Texas
Synchrotron light is used for a wide variety of scientific disciplines ranging from physical chemistry to molecular biology and industrial applications. As the electron beam circulates, random single-particle collisional processes lead to decay of the beam current in time. We report a simulation study in which a combined neural network (NN) and first-principles (FP) model is used to capture the decay in beam current due to Touschek, Bremsstralung, and Coulomb effects. The FP block in the combined model is a parametric description of the beam current decay where model parameters vary as a function of beam operating conditions (e.g. vertical scraper position, RF voltage, number of the bunches, and total beam current). The NN block provides the parameters of the FP model and is trained (through constrained nonlinear optimization) to capture the variation in model parameters as operating condition of the beam changes. Simulation results will be presented to demonstrate that the proposed combined framework accurately models beam decay as well as variation to model parameters without direct access to parameter values in the model.
Fermilab, Batavia, Illinois
ANL, Argonne, Illinois
Northern Illinois University, DeKalb, Illinois- experimental results for a laser-based mock-up of the EO experiment* and
- a design for a beam-based, single-shot, EO sampling experiment using the e-beam from the Argonne Wakefield Accelerator (AWA) RF photoinjector.
The free space electro-optical (EO) sampling technique is a powerful tool for analyzing the longitudinal charge density of an ultrashort e-beam. In this paper, we present
* Yuelin Li, Appl. Phys. Lett. 88, 251108, 2006
LBNL, Berkeley, California
SLAC, Menlo Park, California
We present the results of measurements of the electron cloud intensity in the PEP-II low energy ring (LER) by propagating a TE wave into the beam pipe. Connecting a pulse generator to a beam position monitor button we can excite a signal above the vacuum chamber cut-off and measure its propagation with a spectrum analyzer connected to another button a few meters away. The measurement can be performed with different beam conditions and also at different settings of the solenoids used to reduce the build up of electrons. The presence of a modulation in the TE wave transmission, synchronous with the beam revolution frequency and only measurable with the solenoids off, would be directly correlated to the intensity of the electron cloud phenomenon in the relative region of the ring. In this paper we present and discuss our measurements taken near Interaction Region 12 on the LER, during 2006 and early 2007.
LBNL, Berkeley, California
LBNL, Berkeley, California
Streak camera is an important diagnostic device in the studies of laser plasma interaction, the detailed structure of photo reaction from material science to biochemistry, and in the measurement of the longitudinal distribution of a beam in accelerators. In this paper, we report on a new method which can potentially improve the temporal resolution of a streak camera down to femtoseconds. This method uses a time-dependent acceleration field to defocus the photo electrons longitudinally. This not only reduces the time dispersion distortion caused by initial energy spread but also mitigates the effects from the space-charge forces. An illustration of the method shows significant improvement of the modulation transfer function (MFT) compared with the conventional design.
LBNL, Berkeley, California
The Fermilab main injector (MI) is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort. This upgrade will involve a significant increasing of the bunch intensity relative to its present value. Such an increase will place the MI in a regime in which electron-cloud effects are expected to become important. We have used the electrostatic particle-in-cell code WARP, recently augmented with new modeling capabilities and simulation techniques, to study the dynamics of beam-electron cloud interaction. This study involves a systematic assesment of beam instabilities due to the presence of electron clouds.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
LBNL, Berkeley, California
Plans for the RHIC luminosity upgrade call for an electron cooling system that will place substantial demands on the energy, current, brightness, and beam quality of the electron beam. In particular, the requirements demand a new level of fidelity in beam dynamics simulations. New developments in MaryLie/IMPACT have improved the space-charge computations for beams with large aspect ratios and the beam dynamic computations for rf cavities. We present the results of beam dynamics simulations that include the effects of space charge and nonlinearities, and aim to assess the tolerance for errors and nonlinearities on current designs for a super-conducting ERL.
UMD, College Park, Maryland
We present strong evidence of the observation of optical transition radiation (OTR) from aluminized silicon targets intercepting the UMER 10 keV, 100 ns pulsed electron beam, using fast (300ps and 1ns rise time) photomultiplier tubes. An intensified gated (3ns-1ms) CCD camera is used to image the beam using OTR and to study its time evolution throughout the beam pulse. A comparison of wave forms and time resolved OTR images is presented along with time integrated images obtained with phosphor screens for different initial conditions, i.e. beam currents and gun bias voltages.
correspondance email: rfiorito@umd.edu
ANL, Argonne, Illinois
UMD, College Park, Maryland
We have developed a new optical diffraction radiation (ODR) - dielectric foil radiation interferometer to measure the divergence of the low energy (8 - 14 MeV) ANL - Advanced Wakefield Accelerator electron beam. The interferometer employs an electro-formed micromesh first foil, which overcomes the inherent scattering limitation in the solid first foil of a conventional OTR interferometer, and an optically transparent second foil. The interference of forward directed ODR from the mesh and optical radiation from the dielectric foil is observed in transmission. This geometry allows a small gap between the foils (1 - 2 mm), which is required to observe fringes from two foils at low beam energies. Our measurements indicate that a single Gaussian distribution is sufficient to fit the data.
correspondance email: shkvar@umd.edu
Northern Illinois University, DeKalb, Illinois
Electrons impinging on a thin metallic foil are seen to deliver small bursts of transition radiation (TR) as they cross the boundary from one medium to the next. A popular diagnostic application is found for compact electron bunches. In this case they will emit radiation more or less coherently with an N-squared enhancement of the intensity on wavelengths comparable to the bunch size, generating coherent transition radiation (CTR). Several detailed analytical descriptions have been proposed for describing the resulting spectral distribution, often making different simplifying assumptions. Given that bunches tenths of millimeters long can generate measurable spectra into the millimeter range, concern may arise as to weak diffraction effects produced by optical interference devices containing elements with dimensions in the centimeter range. The work presented here is a report on an upcoming graduate thesis exploring these effects as they apply to the Fermilab/NICADD photoinjector laboratory using a minimal C++ code that implements the methods of virtual quanta and vector diffraction theory.
FEL/Duke University, Durham, North Carolina
PKU/IHIP, Beijing
FEL/Duke University, Durham, North Carolina
One of critical beam parameters for the storage ring based light sources is the energy spread of the electron beam. An accurate measurement of the energy spread remains a challenge. It is well known that the electrons with different energies can degrade the spontaneous emission spectrum of a two-wiggler system in an optical-klystron configuration. The reduced modulation in the spectrum can be used to determine the energy spread of the beam. This paper describes our newly developed energy spread measurement system employing a scanning spectrometer and a fast CCD. A fast CCD with a burst mode of operation is used so that dynamical changes of the energy spread from tens of microseconds to tens of milliseconds can be measured. This system will be used in the beam instability research and free-electron laser research. Together with compact wigglers, such a system can be developed as a dedicated beam diagnostic for storage rings and linacs.
FEL/Duke University, Durham, North Carolina
FEL/Duke University, Durham, North Carolina
The betatron tune measurement system is one of the most important diagnostics for any circular accelerator. During the commissioning of a booster synchrotron newly developed for top-off injection into the Duke storage ring, a versatile tune measurement system employing a photomultiplier tube (PMT) and a space filter has been developed to provide reliable measurements for low current operation at a few micro-amperes of beam-current. Using the turn-by-turn technique, this tune measurement system is being used as a live tune monitor during the booster energy ramping. This system has also be used to measure chromaticity and other important beam parameters. In this paper, we describe the tune measurement system in detail and report our most recent experimental results using this system.
CERN, Geneva
NU, Evanston
A non-destructive bunch length detector has been installed in the CLIC Test Facility (CTF3). Using a series of down-converting mixing stages and filters, the detector analyzes the power spectrum of the electromagnetic field picked-up by a single waveguide. This detector evolved from an earlier system which was regularly used for bunch length measurements in CTF2. Major improvements are increase of frequency reach from 90 GHz to 170 GHz, allowing for sub-pico second sensitivity, and single shot measurement capability using FFT analysis from large bandwidth waveform digitisers. The results of the commissioning of the detector in 2006 are presented.
Alfred University, Alfred, New York
CLASSE, Ithaca
CESR-LEPP, Ithaca, New York
CMU, Pittsburgh, Pennsylvania
A fast vertical beam profile monitor has been implemented at the Cornell Electron Storage Ring (CESR). Readout is based on the Hamamatsu H7260K multianode photomultiplier. This device has a 32 channel linear anode array with 1 mm channel pitch and sub-nanosecond rise time. It provides the ability to probe individual electron and position bunches which are separated by 14 ns within the trains in CESR. A custom 72 MHz digitizer unit allows synchronous multibunch and turn-by-turn data acquisition. An on-board digital signal processor provides local data processing capability. This system provides the capability to probe a range of single bunch and multibunch beam dynamics issues as well as machine stability issues. In this paper we describe the profile monitor hardware, data acquisition system, calibration of the profile monitor, and data analysis software.
LLNL, Livermore, California
Traditionally, thin metal foils are employed for optical transition radiation (OTR) beam diagnostics but the possibility of plating or shorting accelerator insulating surfaces precludes their routine use on high-demand machines. The successful utilization of dielectric foils in place of metal ones would alleviate this issue but necessitates more modeling and understanding of the OTR data for inferring desired beam parameters because of the dielectric's finite permittivity. Additionally, the temperature dependence of the relevant foil parameters must be accounted for due to instantaneous beam heating. Here, we analyze quartz and kapton foil OTR data from the Flash X-Ray (FXR) induction linear accelerator using a model that includes these effects and discuss the resultant FXR beam profiles.
LANL, Los Alamos, New Mexico
TechSource, Santa Fe, New Mexico
In order to better understand the two stream e-p instability issue in the LANSCE Proton Storage Ring, a new diagnostic instrument has been developed to measure the electron cloud formation and trapping in a quadrupole magnet at the LANSCE, PSR. The device called the Electron Cloud Detector (ECD) was fabricated and has successfully been installed in the PSR. Along with the Electron Cloud Detector, an additional device was developed to manipulate electrons ejected from the quadrupole and allow additional information to be obtained from ECD measurements. This paper will discuss the mechanical design and fabrication issues encountered during the course of developing both devices.
BNL, Upton, Long Island, New York
UCLA, Los Angeles, California
STI, Washington
SLAC, Menlo Park, California
Two compressed electron beam bunches from a single 60-MeV bunch have been generated in a reproducible manner during compression in the magnetic chicane - "dog leg" arrangement at ATF. Measurements indicate they have comparable bunch lengths (~100-200 fs) and are separated in energy by ~1.8 MeV with the higher-energy bunch preceding the lower-energy bunch by 0.5-1 ps. Some simulation results for analyzing the double-bunch formation process are also presented.
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
A 9-cell standing wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Laboratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid-Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a pi phase advance per cell. At the maximum deflecting voltage of 500 kV, the theoretical resolution limit of the device is 50 fs, although with current beam parameters and a spot size of 460 microns RMS the effective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application: measuring the temporal current profile of ramped electron bunches generated using the Neptune dogleg compressor, and we present the first measurements of the electron beam current profile obtained using the deflecting cavity.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
A typical diagnostic used to determine the bunch length of ultra-short electron bunches is the autocorrelation of coherent transition radiation. This technique can produce artificially short bunch length results due to the attenuation of low frequency radiation if corrections for the material properties of the Michelson interferometer and detector response are not made. Measurements were taken using FTIR spectroscopy to determine the absorption spectrum of various materials and the response of a Molectron P1-45 pyroelectric detector. The material absorption data will be presented and limitations on the detector calibration discussed.
SLAC, Menlo Park, California
Pavilion Technologies, Inc, Austin, Texas
The primary contributing factors to electron beam lifetime in a storage ring are elastic and inelastic gas scattering, and intrabeam scattering. In order to further quantify the relative contributions of each mechanism, a series of measurements using vertical scraper position and rf-voltage sweeps were performed in SPEAR3 with fill patterns featuring different single-bunch and total beam currents. In parallel, an analytic beam-lifetime simulator was developed taking scattering cross-sections, rf-bucket height and bunch lengthening effects into account. In this paper, we compare measured results with the simulated results in an effort to develop a comprehensive model for electron beam lifetime under a variety of operating conditions.
SLAC, Menlo Park, California
LBNL, Berkeley, California
To maximize luminosity, a feedback system adjusts the relative transverse (x,y) position and vertical angle (y') of the electron and positron beams at the interaction point (IP) of PEP-II. The original system sequentially moved ("dithered") the electrons in four steps per coordinate. Communication with DC corrector magnets and field penetration through copper vacuum chambers led to a full-cycle time of 10 s. Machine tuning can move the beams at the IP and so had to be slowed to wait for the feedback. A new system installed in 2006 simultaneously applies a small sinusoidal dither to all three coordinates at 73, 87 and 103 Hz. Air-core coils around stainless-steel chambers give rapid field penetration. A lock-in amplifier at each frequency detects the magnitude and phase of the luminosity's response. Then corrections for all coordinates are determined using Newton's method, based on convergence from prior steps, and are applied by the same DC correctors used previously but with only one adjustment per cycle for an expected ten-fold increase in speed. We report on the commissioning of this system and on its performance in maintaining peak luminosity and aiding machine tuning.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
Particles are leaving the meter-long plasma wakefield accelerator with a large energy spread. To determine the spectrum of these particles, four diagnostics have been set up. These were used to determine energies of the particles that gain energy in the plasma, those that lose energy by driving the wake and the self-injected particles that are accelerated from rest.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC showed trapping of plasma electrons. These trapped electrons appeared on an energy spectrometer with smaller transverse size than the beam driving the wake. A connection is made between transverse size and emittance; due to the spectrometer?s resolution, this connection allows for placing an upper limit on the trapped electron emittance. The upper limit for the lowest normalized emittance measured in the experiment is 1 mm∙mrad.
SLAC, Menlo Park, California
The ultra-short bunches of the electron beam for LCLS are generated in two 4-dipole bunch compressors located at energies of 250 MeV and 4.3 GeV. Although an absolute measurement of the bunch length can be done by using a transverse deflecting cavity in an interceptive mode, a non-interceptive single shot method is needed as a relative measurement of the bunch length used in the continuous feedback for beam energy and peak current. We report on the design and implementation of two monitors measuring the integrated power of coherent edge radiation from the last dipole in each chicane. The first monitor is installed in early 2007 and we compare its performance with the transverse cavity measurement and other techniques.
Stanford University, Stanford, Califormia
SLAC, Menlo Park, California
The laser acceleration experiments conducted for the E163 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser used to generate the electrons. This system shows rms timing stability better than 1 psec. Temporal synchronicity between the 0.5 psec electron bunch, and the 0.5 psec laser pulse is also of great importance. Cherenkov radiation is used to measure the arrival time of the electron bunch with respect to the laser pulse, and the path length of the laser transport is adjusted to optimize temporal overlap. A linear stage mounted onto a voice coil is used to make shot-by-shot fine timing adjustments to the laser path. The final verification of the desired time stability and control is demonstrated by observing the peak of the laser-electron interaction signal over the course of several minutes.
OXFORDphysics, Oxford, Oxon
SLAC, Menlo Park, California
Fermilab, Batavia, Illinois
LLNL, Livermore, California
We report on measurements of picosecond bunch lengths and the energy-z correlation of the bunch with a high energy electron test beam to the A-line and End Station A (ESA) facilities at SLAC. The bunch length and the energy-z correlation of the bunch are measured at the end of the linac using a synchrotron light monitor diagnostic at a high dispersion point in the A-line and a transverse RF deflecting cavity at the end of the linac. Measurements of the bunch length in ESA were made using high frequency diodes (up to 100 GHz) and pyroelectric detectors at a ceramic gap in the beamline. Modelling of the beam's longitudinal phase space through the linac and A-line to ESA is done using the 2-dimensional tracking program LiTrack, and LiTrack simulation results are compared with data. High frequency diode and pyroelectric detectors are planned to be used as part of a bunch length feedback system for the LCLS FEL at SLAC. The LCLS also plans precise bunch length and energy-z correlation measurements using transverse RF deflecting cavities.
Based on numerical solution of the Fokker-Plank Equation we study the effect of longitudinal damping on the modulation of the bunch length in a storage ring with high RF voltage and momentum compaction
SLAC, Menlo Park, California
The development of an electron cloud in the vacuum chambers of high intensity positron and proton storage rings may limit machine performance. The suppression of electrons in a magnet is a challenge for the positron damping ring of the International Linear Collider (ILC) as well as the Large Hadron Collider. Simulation show that grooved surfaces can significantly reduce the electron yield in a magnet. Some of the secondary electrons emitted from the grooved surface return to the surface within a few gyrations, resulting in a low effective secondary electron yield (SEY) of below 1.0 A triangular surface is an effective, technologically attractive mitigation with a low SEY and a weak dependence on the scale of the corrugations and the external magnetic field. A chamber with triangular grooved surface is proposed for the dipole and wiggler sections of the ILC and will be tested in PEP-II in 2007. The strategy of electron cloud control in ILC and the optimization of the grooved chamber such as the SEY, impedance as well as the manufacturing of the chamber, are also discussed.
SLAC-PUB-11933 & NIMA in publication
SLAC, Menlo Park, California
Ion induced beam instability is one critical issue for the electron damping ring of the International Linear Collider (ILC) due to its ultra small emittance of 2pm. Bunch train filling pattern is proposed to mitigate the instability and bunch-by-bunch feedback is applied to suppress it. Multi-bunch train fill pattern is introduced in the electron beam to reduce the number of trapped ions. Our study shows that the ion effects can be significantly mitigated by using multiple gaps. However, the beam can still suffer from the beam-ion instability driven by the accumulated ions that cannot escape from the beam during the gaps. The effects of beam fill pattern, emittance, vacuum and various damping mechanism are studied using self-consistent program, which includes the optics of the ring.
SLAC, Menlo Park, California
BNL, Upton, Long Island, New York
SLAC, Menlo Park, California
Jefferson Lab, Newport News, Virginia
For accelerator projects with ultra short electron beam, beam dynamics study has to invoke the short-range wakefield. In this paper, we first obtain the short-range dipole mode resistive wall wakefield. Analytical approach is then developed to study the single bunch transverse beam dynamics due to this short-range resistive wall wake. The results are applied to the LCLS undulator and some other proposed accelerators.
PPPL, Princeton, New Jersey
A numerical scheme for the electromagnetic particle simulation of high-intensity charged-particle beams has been developed which is a modification of the Darwin model. The Darwin model neglects the transverse induction current in Ampere?s law and therefore eliminates fast electromagnetic (light) waves from the simulations. The model has been incorporated into the nonlinear delta-f Beam Equilibrium Stability and Transport(BEST) code. As a benchmark, we have applied the model to simulate the transverse electromagnetic Weibel-type instability in a single-species charged-particle beam with large temperature anisotropy. Results are compared with previous theoretical and numerical studies using the eighenmode code bEASt. The nonlinear stage of the Weibel instability is also studied using BEST code, and the mechanism for nonlinear saturation is identified.
BNL, Upton, Long Island, New York