ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The Advanced Photon Source (APS) is a third-generation storage-ring-based x-ray source that has been operating for more than 11 years and is enjoying a long period of stable, reliable operation. While APS is presently providing state-of-the-art performance to its large user community, we must clearly plan for improvements and upgrades to stay at the forefront scientifically. Significant improvements should be possible through upgrades of beamline optics, detectors, and end-station equipment, along with local, evolutionary changes to the storage ring itself. However, major accelerator upgrades are also being investigated. One very promising option that has been the subject of considerable research is the use of an energy recovery linac. In this option, APS would transition from a source based on a stored electron beam to one based on a continuously generated high-brightness electron beam from a linac. Such a source promises dramatically improved brightness and transverse coherence compared to third-generation storage rings, as well as distinctly different temporal properties.
HU/AdSM, Higashi-Hiroshima
Nagoya University, Nagoya
High brightness electron source is a key technology for future projects based on advanced accelerators. Although GaAs photo-cathode is very attractive because it can generate highly polarized and extremely high brightness electron beam, the limited operational life time is a technical issue. In Hiroshima University, a photo-cathode test bench is implemented for various studies of GaAs photo-cathode. Super high vacuum, 9E-9Pa, was achieved and the cathode was successfully activated by processes of heat cleaning technique and the alternate evaporation of Cs and oxygen. The quantum efficiency and its lifetime were investigated as a function of cathode temperature, simulating temperature rise by the high power cathode drive laser. Wavelength dependence was also investigated.
INFN/LNF, Frascati (Roma)
In this paper we report the status of the SPARC photocathode drive laser system. In the high brightness photoinjector the properties of the electron beam are directly related to the drive laser features. In fact the 3-D distribution of the electron beam and the time of emission are determined by the incoming laser pulse. The SPARC laser is a 10 Hz frequency-tripled TW-class Ti:Sa commercial system. A dedicated activity on the shape of the laser pulse has been performed in order to produce high energy UV flat top and multi-peaks time profile. To achieve the required flat top shape we perform a manipulation of the laser spectrum at the fundamental wavelength and directly at the third harmonic. The production of multi peaks laser pulse have been studied and tested. Finally we present the key laser performances recorded for the SPARC FEL experiment.
LBNL, Berkeley, California
Funding: This work was supported by the Office of Science, U. S. Department of Energy, under Contract No. DE-AC02-05CH11231.
The Advanced Photoinjector Experiment (APEX) seeks to validate the design of a proposed high-brightness, normal conducting RF photoinjector gun and bunching cavity feeding a superconducting RF linac to produce nC-scale electron bunches with sub-micron normalized emittances at MHz-scale repetition rates. The beamline design seeks to optimize the slice-averaged 6D brightness of the beam prior to injection into a high gradient linac for further manipulation and delivery to an FEL undulator. Details of the proposed beamline layout and electron beam dynamics studies are presented.
TUE, Eindhoven
Pulsar Physics, Eindhoven
Ultrafast electron diffraction (UED) enables single-shot studies of structural dynamics at atomic length and time scales, i.e. 0.1 nm and 0.1 ps. At present UED experiments are based on femtosecond laser photoemission from solid state cathodes. We propose a new type of electron source, based on near-threshold photoionization of a laser-cooled and trapped atomic gas. The electron temperature of these sources can be as low as 10 K. This implies an increase in brightness by orders of magnitude and enables single-shot studies of, e.g., biomolecular samples. In this contribution we numerically investigate the performance of a laser-cooled electron source by GPT tracking simulations with realistic fields and all pairwise Coulomb interactions.
LBNL, Berkeley, California
SLAC, Menlo Park, California
Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contracts No. DE-AC02-05CH11231 (LBNL) and DE-AC02-76SF00515 (SLAC).
The future directions of x-ray science and the photon beam properties required to pursue them were recently evaluated by a joint LBNLSLAC study group*. As identified by this group, essential x-ray capabilities for light sources in the future (but not necessarily from any single source) include: 1) x-ray pulses with Fourier-transform-limit time structure from the picosecond to attosecond regime, synchronized with conventional lasers, and with control of longitudinal pulse shape, amplitude and phase; 2) full transverse coherence; 3) high average flux and brightness; 4) energy tunability in soft and hard x-ray regimes, and polarization control. Metrics characterizing source properties include not only average and peak spectral brightness but also the photons per pulse and repetition rate as a function of pulse length, and the proximity to transform-limited dimensions in six dimensional phase space. We compare the projected performance of various advanced x-ray source types, with respect to these metrics and discuss their advantages and disadvantages. We briefly discuss the technology challenges for future sources and the areas of R&D required to address them.
*R. Falcone, J. Stohr et al., “Scientific Needs for Future X-Ray Sources in the U.S. - A White Paper”, SLAC-R-910, LBNL-1090E, October 2008.
ANL, Argonne
Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
ERL staging is a novel concept that provides a practical path to upgrading an existing synchrotron light source while minimizing disruption to the users and managing the technical risk. In the very first stage, the accelerator operating parameters are comparable to CEBAF without recirculation. Therefore, initially, energy recovery is not required and the injector is more modest. Consequently, the technical risk is significantly reduced relative to the full ERL. Using the APS as an example, the first stage is based on a full-energy, 7-GeV superconducting radiofrequency (srf) linac and an electron source that is almost off-the-shelf. The linac would initially deliver a low average current beam (<200 uA), but with a geometric emittance that is much smaller than the storage ring, the x-ray brightness can exceed the APS. Furthermore, the spatial coherence fraction would be about 100 times higher and the pulse length up to 100 times smaller than the APS. Valuable srf operating experience is attained at an early stage while allowing critical energy recovery issues to be studied. Energy recovery is commissioned in stage 2. The optics design and performance at each stage will be presented.
LLNL, Livermore, California
Funding: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Recently, a drive laser for an 2.86 GHz rf photoinjector, designed to provide a pulse that has a flat temporal and spatial profile, has been built, commissioned, and put into service as part of the LLNL Compton-scattering source program. This laser is based on an all-fiber oscillator and front-end amplification system, and provides both the laser light to generate the electrons as well as the rf signal that is amplified to accelerate them. Now, a new 11.424 GHz photoinjector is being developed, which has required a revised design of for the laser system. The higher frequency has placed more stringent requirements on the synchronization stability, delivered pulse length, and pulse rise times to maintain the desired emittance. Presented here are the overall design and measured performance of the current system and a discussion of what changes are being made to address observed shortcomings and more demanding requirements to make the system ready for the next-generation Compton-scattering source.
KEK, Ibaraki
Thick carbon foils (>300 ug/cm2)has been used for stripping of H- ion beam at the 3GeV Rapid Cycling Synchrotron (3GeV-RCS) of J-PARC, where foils with long lifetime against high temperature >1800 °K are strongly required for efficient accelerator operations. The key parameter to the foil lifetime is foil temperature attained during irradiation. We have recently developed a new irradiation system for lifetime measurement using the KEK 650 keV Cockcroft-Walton accelerator with high current pulsed and dc H- beam, which can simulate the high-energy depositions upon foils in the RCS. During irradiation tests by this system, the temperature of foil is measured by a thermometer in a dc mode, and by using a photo-transistor in a pulsed mode. This paper describes the pulsed measurements with 5-10 mApeak, 0.1-0.5 msec duration and 25 Hz repetition.
SLAC, Menlo Park, California
Stanford University, Stanford, California
UCLA, Los Angeles, California
Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
SSRL and SLAC groups are developing a long-range plan to transfer its evolving scientific programs from the SPEAR3 light source to a much higher performing photon source that would be housed in the 2.2-km PEP-II tunnel. While various concepts for the PEP-X light source are under consideration, including ultimate storage ring and ERL configurations, the present baseline design is a very low-emittance storage ring. A hybrid lattice has DBA or QBA cells in two of the six arcs that provide a total ~30 straight sections for ID beam lines extending into two new experimental halls. The remaining arcs contain TME cells. Using ~100 m of damping wigglers the horizontal emittance at 4.5 GeV would be ~0.1 nm-rad with >1 A stored beam. PEP-X will produce photon beams having brightnesses near 1022 at 10 keV. Studies indicate that a ~100-m undulator could have FEL gain and brightness enhancement at soft x-ray wavelengths with the stored beam. Crab cavities or other beam manipulation systems could be used to reduce bunch length or otherwise enhance photon emission properties. The present status of the PEP-X lattice and beam line designs are presented and other implementation options are discussed.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515
SLAC National Accelerator Laboratory is studying an option of building a high brightness synchrotron light source machine, PEP-X, in the existing PEP-II tunnel*,**. By replacing 6 arcs of FODO cells of PEPII High Energy Ring (HER) with two arcs of DBA and four arcs of TME and installation of 89.3 m long damping wiggler an ultra low beam emittance of 0.14 nm-rad (including intra-beam scattering) at 4.5 GeV is achieved. In this paper we study the possibility to further reduce the beam emittance by releasing the constraint of the dispersion free in the DBA straight. The QBA (Quadruple Bend Achromat) cell is used to replace the DBA. The ratio of outer and inner bending angle is optimized. The dispersion function in the non-dispersion straight is controlled to compromise with lower emittance and beam size at the dispersion straight. An undulator of period length 23 mm, maximum magnetic field of 1.053 T, and total periods of 150 is used to put in the 30 straights to simulate the effects of these IDs on the beam emittance and energy spread. The brightness including all the ID effects is calculated and compared to the original PEP-X design.
*R. Hettel et al., “Ideas for a Future PEP-X Light Source”, EPAC08, p.2031(2008).
**M-H Wang et al., “Lattice Design of PEP-X as a Light Source Machine at SLAC”, EPAC08, p.2127(2008).
LNLS, Campinas
We present an overview of a new synchrotron radiation source currently being designed at the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas. The LNLS-1 light source, based on a 1.37 GeV storage ring, has been in routine operation since 1997. The LNLS-2 light source will consist of an injector system and a low emittance 2.5 GeV electron storage ring capable of delivering undulator radiation with average brightness in excess of 1020 photons/sec/0.1%/mm2/mrad2 in the few hundred eV to several tens of keV photon energy range. High flux radiation up to 100 keV will also be available with the use of superconduting wigglers. In this work, we present the basic design considerations and parameters for a proposed magnetic lattice for LNLS-2, with special attention to providing solutions for the realization of low emittance which are cost effective regarding both the construction investment as well as the operation of the facility. In particular, the possibility of the large scale use of permanent magnet technology for the storage ring lattice magnets is discussed.
INFN/LNF, Frascati (Roma)
High gain free electron lasers require the production of a high brightness electron beam that is a low emittance, high current beam. To this aim the injector and linac design and theirs operation are the leading edge. The successful operation of the SCSS FEL driven by a C-band linac has demonstrated that C-band is a mature technology and it is very attractive in terms of gradient and compactness. In this paper it is described a beam dynamics study, made with the Homdyn code, for a C-band linac driven FEL with S-band photo-injector. The key point is to match the longitudinal phase space of the S-band photo-injector with the C-band linac using the velocity bunching technique. The result is a brightness up to 1015A/m2, obtained with a low emittance and a relaxed peak current.
LBNL, Berkeley, California
Funding: Work supported by the Director, Office of Science, U. S. Department of Energy under Contract No. DE-AC02-05CH11231.
Multiobjective optimization has been used in many fields including accelerator related projects. Here we use it as a powerful tool for lattice design and optimization, which includes betatron functions, brightness.
CERN, Geneva
At present, for most LHC type physics beams, six buckets of the PS operated with harmonic number h=7 are filled in two transfers, and each of the PS Booster rings provides only one bunch. The scheme presented aims at replacing the double batch transfer by a single batch transfer and is of interest (i) for the nominal 25 ns LHC beams once the Booster injection energy has been increased after completion of Linac4 and (ii) already now for 50 ns and 75 ns LHC beams less demanding for the Booster in terms of beam brightness. Two bunches with the correct spacing must be generated in the Booster rings by superposition of an h=2 RF system and a smaller h=1 component. Theoretical considerations and first experimental results will be presented.
TRIUMF, Vancouver
DAE/VECC, Calcutta
TRIUMF proposes a 1/2 MW electron linac (e-linac) for radioactive ion beam production via photofission. The e-linac is to operate CW using 1.3 GHz superconducting (SC) technology. The accelerator layout consists of a 100 keV thermionic gun, a normal conducting buncher, an injector module, and main linac modules accelerating to a final energy of 50 MeV. The design beam current is 10 mA. The beam dynamics of the injector, where electrons make the transition to the fully relativistic state, has been identified as the most critical part of the design and is the subject of simulations (starting at the gun cathode) using realistic EM fields in PARMELA and TRACK. CW operation demands the novel choice of adopting an SC capture section. A preliminary design of the injector foresees a capture section composed either of two independent or two coupled single-cell cavities, beta <1, that increase the energy to about 500 keV, followed by one nine-cell cavity that boosts the energy up to 10 MeV. The design parameters are subjected to a global optimization program. In this paper we present results from the beam dynamics study as well as details and final outcome of the optimization process.
NIRS, Chiba-shi
TIT, Yokohama
The screen monitor system is an important tool for beam diagnostic of the high-energy-beam transport line at the Heavy-Ion Medical Accelerator in Chiba (HIMAC). We have developed a very thin fluorescent film and high speed charge-coupled-device camera. Because the fluorescent film is very thin (ZnS:Ag 2mg/cm3), the beam is measured with semi-non-destructively. Consequently we can use more than two monitors at the same time and multiple locations. Moreover we employ a high-speed three-processer for image processing, the system can be applied for online monitoring and interlock system (100Hz). When the beam profile measured by this system is inevitably changed over the setting tolerance during therapeutic irradiation for the patient, the beam is immediately turned off. The design and measurement result by irradiation test are discussed.
USTC/NSRL, Hefei, Anhui
Funding: National “985 Project” （173123200402002); National Natural Science Foundation(10875117)
A new high brightness injector is planned to be installed at HLS, NSRL. It is based on a new photocathode RF electron gun. To steer the beam along the optimal trajectory, higher precision controlling of beam position is required. The positional resolution of the BPM system designed for the new RF gun should be higher than 10 μm. A new cavity BPM design is then given instead of old stripline one because of its higher positional resolution. In a normal symmetrical pill-box BPM design, machining tolerance will result in x-y coupling, which will cause cross-talk problem. A novel design is then presented here. To solve the problem before, a position cavity which has a racetrack cross section is used instead of a pill-box one. The ideal resolution of this design could be less than 3 nm.
USTC/NSRL, Hefei, Anhui
A high brightness injector has been developing in HLS (Hefei Light Source), and the design of beam parameter measurement system is presented in this paper. The whole system will measure beam position, beam current, emittance of beam, bunch length, beam energy and energy spread. For the beam position, we have designed three types of BPMs: stripline BPM, with the resolution of 20 μm; cavity BPM, with the resolution of 10 μm, and resonant stripline BPM*. The beam position processor Libera will be used. The beam current will measured using the ICT and FCT. When going out of the gun, the energy of the beam is about 4MeV 5MeV, and the emittance of the beam is charge-dominated, so we use a set of slits with the width of 90 μm to split the beam to beamlets. The bunch length is measured using OTR and streak camera. Before entering the bending magnet, the beam will go pass a very narrow slit, with the width of 90 μm, and the resolution of energy spread will be improved.
*M.Dehler, “Resonant Strip line BPM for Ultra Low Current Measurements”, Proceedings of DIPAC 2005, Lyon, France, p.286-288
LBNL, Berkeley, California
Funding: Supported by DOE BES contract DE-AC03-76SF00098.
Recently there has been a proposal to use pulsed high order multipole elements for injection. One of the advantages of this proposed injection scheme would be that it would be less disruptive to the stored beam and thus advantageous for Top-off operation. In addition to Top-off, such novel injectors might open the door to operating storage rings in more desirable lattice settings. In this paper we will explore some of the possibilities for taking advantage of high order multipole pulsed kick injection.
RadiaBeam, Marina del Rey
UCLA, Los Angeles, California
The accelerator community has many codes that model beams and emitted radiation. Many of these codes are specialized and often, as in start-to-end simulations, multiple codes are employed in subsequent fashion. One of the most important goals of simulations is to accurately model beam parameters and compare results to those obtained from real laboratory diagnostics. This paper describes the development of a user-friendly code that models the coherent radiation of high brightness beams, with a heavy emphasis on simulation of observables via laboratory diagnostics.