INFN/LNF, Frascati (Roma)
INFN-Milano, Milano
INFN-Roma II, Roma
UCLA, Los Angeles, California
ENEA C. R. Frascati, Frascati (Roma)
INFN-Roma, Roma
Vanderbilt University, Nashville, Tennessee
DESY, Hamburg
GANIL, Caen
The Eurisol heavy ion post-accelerator and the Spiral2 deuton/ion MEBT should transport a continuous wave (cw) beam from respectively a 88.05 MHz RFQ (β respectively 0.036 and 0.04) to a drift-tube linac. A high frequency chopper is being studied to select only 1 bunch over N, 10 < N < 10000 as asked by the physicists. It requires pulses higher than 3 kV, rising in less than 7 ns at a repetition rate up to 8.8 MHz. These figures are at the border of what can be provided by the travelling wave fast choppers and the capacitive-type chopping technologies. We have reviewed the current fast and slow chopping structures and their associated pulse generator. Some preliminary RF simulations to adapt the present chopping devices to our requirements are presented. The main limitations of these technologies when applied to isolate bunches in ion cw accelerators are also shown. Our first studies and results to solve the arising problems are discussed.
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
DESY, Hamburg
KEK, Ibaraki
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
Hiroshima University, Higashi-Hiroshima
Visual Information Center, Inc., Ibaraki-ken
KEK, Ibaraki
JAEA, Ibaraki-ken
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
JAEA/LINAC, Ibaraki-ken
The XAL application development environment has been installed as a part of the control system for the Japan Proton Accelerator Research Center (J-PARC). XAL was initially developed at SNS and has been described at length in previous conference proceedings (e.g., Chu et. al. APAC07, Galambos et. al. PAC05, etc.). The fundamental tenet of XAL is to provide a consistent, high-level programming interface, along with a set of high-level application tools, all of which are independent of the underlying machine hardware. Control applications can be built that run at any accelerator site where XAL is installed. Of course each site typically has specific needs not supported by XAL and the framework was designed with this in mind: each institution can upgrade XAL which then is accessible to all users. We outline the upgrades and enhancements to the XAL online model necessary for accurate simulation of the J-PARC linac. For example, we have added permanent magnet quadrupoles and additional space charge capabilities such as off-centered and rotated beams and bending magnets with space charge. We present the physics models for the upgrades as well as the software architecture supporting them.
KEK, Ibaraki
KEK, Ibaraki
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
HUST, Wuhan
A virtual control system designed to control and monitor the process of a cyclotron virtual prototyping is presented in this paper. Based on the feature of cyclotron, a distributed control structure is proposed according to the knowledge of software engineering. LabVIEW is employed to develop human machine interface(HMI), sequential control, safety interlock, and MATLAB is used to implement analysis and simulation. Dynamic data exchange (DDE) supported by Win32 Platform SDK is adopted to process data exchanging by a Server/Client mode. Any additional functions can be extended easily in this system in future.
CERN, Geneva
CERN, Geneva
NTUT, Taipei
NSRRC, Hsinchu
STFC/RAL/ISIS, Chilton, Didcot, Oxon
* M. G. White et al., A 3-BeV High Intensity Proton Synchrotron, The Princeton-Pennsylvania Accelerator, CERN Symp.1956 Proc., p525.
ANL, Argonne, Illinois
Due to the circuit topology of ramping power supplies used in the APS Booster ring, they are unable to follow the linear current ramp to the desired accuracy of 0.1%. In addition, those supplies are also sensitive to AC line perturbation. To improve the performance, a linear regulator using paralleled MOSFET devices in series with the power supply is proposed. The control algorithm uses a real-time current feedback loop to force the MOSFETs to work in the linear operation mode. By using this linear MOSFET regulator, the MOSFETs' drain to source voltage, and hence the voltage imposed on magnets can be regulated very quickly. As a result, the regulation of the magnet current can be improved significantly. So far the simulation results show that with the linear regulator the current regulation can be improved to better than 0.1%. Because of the high bandwidth of the linear regulator, it can reduce the harmonic content in the output current as well as the noises due to the AC line disturbance. A sextupole power supply has been set up to verify the proposed topology. This paper discusses the circuit topology, the regulation algorithm, and the experiment results.
ANL, Argonne, Illinois
The Advanced Photon Source storage ring has several bunch fill patterns for user operation. The hybrids fill pattern consists of a single bunch with a charge of 16 mA and a bunch train of 56 bunches. Both horizontal and vertical instabilities are observed. Currently chromaticity correction is the only method available to overcome the instability. Beamlife time and injection efficiency suffer because of high sextupole currents. A bunch-to-bunch feedback system is designed to overcome beam instability and reduce the required chromaticity correction. The feedback system is based on an FPGA DSP processor. The signal filtering algorithm is based on the time-domain-least-square method developed at SPring-8. We have just completed the integration of the system. We report the system design and some test results.
Muons, Inc, Batavia
Fermilab, Batavia, Illinois
A helical cooling channel consisting of a pressurized gas absorber imbedded in a magnetic channel that provides superimposed solenoidal, helical dipole and helical quadrupole fields has shown considerable promise in providing six-dimensional cooling of muon beams. The analysis of this muon cooling technique with both analytic and simulation studies has shown significant reduction of muon phase space. A particular channel that has been simulated is divided into four segments each with progressively stronger fields and smaller apertures to reduce the equilibrium emittance so that more cooling can occur. The fields in the helical channel are sufficiently large that the conductor for segments 1 and 2 can be Nb3Sn and the conductor for segments 3 and 4 may need to be high temperature superconductor. This paper will describe the magnetic specifications for the channel and two conceptual designs on how to implement the magnetic channel.
Muons, Inc, Batavia
BNL, Upton, Long Island, New York
UMiss, University, Mississippi
The ability of high temperature superconducting (HTS) conductor to carry high currents at low temperatures makes feasible the development of very high field magnets for uses in accelerators and beam-lines. A specific application of a very high field solenoid is to provide a very small beta region for the final cooling stages for a muon collider. This paper will describe a conceptual design of a 50 Tesla solenoid based on Bi-2223 HTS tape, where the magnet will be operated at 4.2 K to take advantage of the high current carrying capacity at that temperature. A 25 Tesla solenoid has been run using a 5 Tesla Bi-2212 insert. The current carrying capacity of the BSCCO wire has been measured to be 266 Amps/mm2 at 4.2 K at the NHFML. This paper will describe the technical issues associated with building this 50 Tesla magnet. In particular it will address how to mitigate the large Lorentz stresses associated with the high field magnet and how to design the magnet to reduce the compressive end forces.
Muons, Inc, Batavia
Fermilab, Batavia, Illinois
MANX is a 6-dimensional muon ionization-cooling experiment that has been proposed to Fermilab to demonstrate the use of a Helical Cooling Channel (HCC) for future muon colliders and neutrino factories. The HCC for MANX has solenoidal, helical dipole, and helical quadrupole magnetic components which diminish as the beam loses energy as it slows down in a liquid helium absorber inside the magnets. Two superconducting magnet system designs are described which use quite different approaches to providing the needed fields. Additional magnets that provide emittance matching between the HCC and upstream and downstream spectrometers are also described as are the results of G4Beamline simulations of the beam cooling behaviour of the complete magnet and absorber system.
KEK, Ibaraki
We present the final results of a study for the design of a fast extraction kicker to be installed in the Accelerator Test Facility ring at KEK. The purpose of this project is to test the technologies to be used in the design of the extraction kickers for the International Linear Collider damping rings. The kicker's rise and fall times are important parameters in the final configuration of the rings, since they constrain the minimum distance between bunches and ultimately define a lower limit for the rings length. We investigated a stripline kicker composed of several 65-cm long sections, grouped in two different locations in the ATF damping ring. An analytical study of the kicker's parameter and extensive computer simulations using Microwave Studio* point out the ambitious requirements on the pulsers, in order to be able to satisfy the design specifications. We also investigated the use of a single kicker module, together with a close orbit bump near the extraction septum.
* http://www.cst.com
Fermilab, Batavia, Illinois
NSCL, East Lansing, Michigan
We present the design of a superferric cyclotron gas stopper magnet that has been proposed for use at the NSCL/MSU to stop the radioactive ions produced by fragmentation at high energies (~140 MeV/u). The magnet is a gradient dipole with three sectors ( B~2.7 T at the center and 2 T at the pole-edge. The magnet outer diameter is 3.8 m, with a pole radius of 1.1 m and B*rho=1.7 T-m). The field shape is obtained by extensive profiles in the iron. The coil cross-section is 64 cm*cm and peak field on the conductor is about 1.6 T. The upper and lower coils are in separate cryostat and have warm electrical connections. We present the coil winding and protection schemes. The forces are large and the implication on the support structure is 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.
* S. S. Kurennoy and J. F. Power, EPAC 2000 (Vienna, Austria, 2000), 336.
SLAC, Menlo Park, California
The LCLC RF gun requires a water cooling thermal system to tune the resonance frequency of the cavity to 2856.03MHz. The RF system operates in pulsed mode with bursts of 2.5usec at a repetition rate of 30-120Hz. The thermal system operates in combination with the low-level RF system to set the operation point of the cavity. The Low-Level RF system controls the magnitude and phase of the cavity voltage and define slow signals to the thermal system. The thermal system operates by pre-heating / pre-cooling the water and mixing both channels to achieve the optimal temperature to control the cavity resonant frequency. The tune control of the RF gun include two systems with different dynamics. The dynamics of the thermal system is slow while the RF system is fast. Additionally, different actuators in the system present limits that introduce non-linearities to be taking into account during the start up process . Combining these characteristics, a controller is designed for the resulting hybrid system that allows convergence in large for all the operation conditions and achieve the performance in the magnitude and phase of the cavity voltage required around the operation point.
SLAC, Menlo Park, California
PEP-II operations will increase the beam currents to 4A for LER and 2.2A for HER to achieve the final goal in luminosity. These magnitudes are challenging in part because they will push toward the limit the longitudinal low-order mode (LOM) beam stability due to beam loading. To analyze the behavior of both rings at high currents and understand the limits in the longitudinal feedback systems a simulation tool has been developed at SLAC. This tool is based on a reduced model of the longitudinal LOM dynamics of the beam interacting with the effective impedance presented by RF station. Simulations and measurements of the longitudinal beam behavior in both rings have been performed to understand the ultimate limit of the system. These studies have defined the impact of control loop parameters in the longitudinal beam dynamics, identified the poor performance of RF devices affecting the optimal performance of the RF stations and quantified the behavior of the longitudinal LOM beam dynamics. Results of sensitivity to parameter variations in the beam dynamics and limits in the maximum current that LER/HER can achieve based on the longitudinal beam stability are reported in this paper.
SLAC, Menlo Park, California
*S. G. Tantawi et al., Physical Review Special Topics – Accelerator and Beams. 8, 042002 (2005)
Jefferson Lab, Newport News, Virginia
For an ongoing high current cryomodule project, a total of 5 higher order mode (HOM) absorbers are required per cavity. The load is designed to absorb RF heat induced by HOMs in a 748.5MHz cavity. Each load is targeted at a 4 kW dissipation capability. Embedded cooling channels are employed to remove the heat generated in ceramic tiles and by surface losses on the waveguide walls. A sequentially coupled RF-thermal-structural analysis was developed in ANSYS to optimize the HOM load design. Frequency dependent dielectric material properties measured from samples and RF power spectrum calculated by the beam-cavity interaction codes were considered. The coupled field analysis capability of ANSYS avoided mapping of results between separate RF and thermal/structural simulation codes. For verification purposes, RF results obtained from ANSYS were compared to those from MAFIA, HFSS, and Microwave Studio. Good agreement was reached and this confirms that multiple-field coupled analysis is a desirable choice in analysis of HOM loads. Similar analysis could be performed on other particle accelerator components where distributed RF heating and surface current induced losses are inevitable.
ORNL, Oak Ridge, Tennessee
The proposed upgrade plan for RF control of the Spallation Neutron Source (SNS) accumulator ring requires that the new digital field control module (FCM) support both the conventional narrow-band feed forward control and a new beam-based feed forward control. Both are necessary for compensating the heavy beam loading in SNS ring. The ring FCM also has the integrated control and monitoring features for the cavity bias, cavity resonance, and tetrode grid boost. A user-friendly Epics GUI for all these FCM functionalities is also a part of the requirement. The ring FCM under development is being implemented on the hardware of the proven FCM of SNS Linac. Both the controller architecture and the design code of the digital hardware for the Linac system will be largely reused in the ring system.
ORNL, Oak Ridge, Tennessee
LANL, Los Alamos, New Mexico
UW-Madison, Madison, Wisconsin
3D computing simulations have been performed to study the magnetic field distribution of the SNS ring extraction Lambertson septum magnet. The magnetic field for extracted beams is fully characterized in all the aspects. The stray field on the circulating beam line and the effect of a shielding box up-stream and a shielding cap down-stream is investigated. In addition, the magnetic interference between the Lambertson and an adjacent quadrupole has been studied. The simulations have provided valuable information for the SNS ring commissioning and operation. This paper reports our simulation techniques and the major results.
University of Pennsylvania, Philadelphia, Pennsylvania
TRIUMF, Vancouver
Eltech University, St. Petersburg
Ceramics Ltd., St. Petersburg
Omega-P, Inc., New Haven, Connecticut
We present recent results on development of a BST(M) ferroelectric composition synthesized for use in advanced technology components for X-band and Ka-band RF systems in high gradient accelerators and offer significant advantages for high power RF manipulation in the 300-1'000 MHz frequency range as well. These low loss ferroelectric materials can be used as key elements of both tuning and phase shifting components. We have identified BST ferroelectric-oxide compounds as suitable materials for a fast electrically-controlled 700 MHz, 50 kW tuner for ERL (BNL) and for high-power fast RF phase shifters to be used for SNS vector modulation applications. We have also developed large diameter (11 cm) BST(M)-based ferroelectric rings planned to be used at high average power (10 kW range) for L-band phase-shifters intended for the ILC. This phase shifter will allow coupling adjustment and control of the power consumption during the process of SC cavity filling.
BNL, Upton, Long Island, New York
The Brookhaven AGS Main Magnet Power Supply (MMPS) is a thyristor control supply rated at 5500 Amps, ±9000 Volts. The peak magnet power is 50 MWatts. The power supply is fed from a motor/generator manufactured by Siemens. The generator is 3 phase 7500 Volts rated at 50 MVA. The peak power requirements come from the stored energy in the rotor of the motor/generator. The motor generator is about 45 years old and Siemens is not manufacturing similar machines in the future. We are therefore investigating different ways of storing energy for future AGS MMPS operation. This paper will present simulations of a power supply where energy is stored in capacitor banks. Two dc to dc converters will be presented. The switching elements would be IGCT's made by ABB. The simulation program used is called PSIM Version 6.1. The control system of the power supply will also be presented. The average power from the Long Island Power Authority (LIPA) into the power supply will be kept constant during the pulsing of the magnets at ±50 MW. The reactive power will also be kept constant below 1.5 MVAR. Waveforms will be presented.
BNL, Upton, Long Island, New York
Large accelerator main magnet system consists of hundreds, even thousands, of dipole magnets. They are linked together under selected configurations to provide highly uniform dipole fields when powered. Distributed capacitance, insulation resistance, coil resistance, magnet inductance, and coupling inductance of upper and lower pancakes make each magnet a complex network. When all dipole magnets are chained together in a circle, they become a coupled pair of very high order complex ladder networks. In this study, a network of more than thousand inductive, capacitive or resistive elements are used to model an actual system. The circuit is a large scale network. Its equivalent polynomial form has several hundred degrees. Analysis of this high order circuit and simulation of the response of any or all components is often computationally infeasible. We present methods to use frequency decomposition approach to effectively simulate and analyze magnet configuration and power supply topologies.
BNL, Upton, Long Island, New York
A main magnet chain forms a pair of transmission lines. Pulse-reflection-caused voltage and current differentiation throughout the magnet chain can have adverse effect on main magnet field quality. This effect is associated with magnet system configuration, coupling efficiency, and parasitic parameters. A better understanding of this phenomenon will help us in new design and existing system upgrade. In this paper, we exam the transmission line effect due to different input functions as well as configuration, coupling, and other parameters.
ORNL, Oak Ridge, Tennessee
The SNS ring and associated transport lines, commissioned in January 2006, are designed to accumulate and deliver up to 1.5·1014, 1 GeV protons at 60 Hz to a liquid mercury target for neutron production. In order to control activation and to allow for routine hands-on maintenance of accelerator components, beam loss in most of the ring must remain below 1 W/m . For the full 1.4 MW beam, this translates to a fractional beam loss limit of 0.01%. Accomplishing this loss limit at full beam power will require successful utilization of the ring's two-stage betatron collimation system. In this paper we present the results of initial collimation experiments. We characterize the collimation-induced beam-loss pattern and compare our results with simulations. In addition, we discuss other existing beam-loss-related challenges in the ring.
Jefferson Lab, Newport News, Virginia
Advances in ionization cooling, phase space manipulations, and technologies to achieve high brightness muon beams are stimulating designs of high-luminosity energy-frontier muon colliders. Simulations of Helical Cooling Channels (HCC) show impressive emittance reductions, new ideas on reverse emittance exchange and muon bunch coalescing are being developed, and high-field superconductors show great promise to improve the effectiveness of ionization cooling. Experiments to study RF cavities pressurized with hydrogen gas in strong magnetic fields have had encouraging results. A 6-dimensional HCC demonstration experiment is being designed and a 1.5 TeV muon collider is being studied at Fermilab. Two new synergies are that very cool muon beams can be accelerated in ILC RF structures and that this capability can be used both for muon colliders and for neutrino factories. These advances are discussed in the context of muon colliders with small transverse emittances and with fewer muons to ease requirements on site boundary radiation, detector backgrounds, and muon production.
Fermilab, Batavia, Illinois
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).
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.
Fermilab, Batavia, Illinois
Illinois Institute of Technology, Chicago, Illinois
* Synergia: A 3D Accelerator Modelling Tool with 3D Space Charge. Journal of Computational Physics, Volume 211, Issue 1 , 1 January 2006, Pages 229-248.
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
IUCF, Bloomington, Indiana
BNL, Upton, Long Island, New York
The Orbit Response Matrix (ORM) has been successfully used extensively in accelerator modeling. However, in many cases, the existing codes can not find a correct model. We develop a new code that solve the convergence and coupling problems. We test our code by carrying out systematic study of accelerator models. Effects measurement errors and the completeness of information will be addressed in this study. Possible inclusion of phase information will be discussed.
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.
CEA, Gif-sur-Yvette
SLAC, Menlo Park, California
Under the support of the U. S. DOE SciDAC program, SLAC has been developing a suite of 3D parallel finite-element codes aimed at high-accuracy, high-fidelity electromagnetic and beam physics simulations for the design and optimization of next-generation particle accelerators. Running on the latest supercomputers, these codes have made great strides in advancing the state of the art in applied math and computer science at the petascale that enable the integrated modeling of electromagnetics, self-consistent Particle-In-Cell (PIC) particle dynamics as well as thermal, mechanical, and multi-physics effects. This paper will present 3D results of trapped mode calculations in an ILC cryomodule and the modeling of the ILC Sheet Beam klystron, shape determination of superconducting RF (SCRF) cavities and multipacting studies of SCRF HOM couplers, as well as 2D and preliminary 3D PIC simulation results of the LCLS RF gun.
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
Fermilab, Batavia, Illinois
NRL, Washington, DC
SAIC, Burlington, Massachusetts
Low emittance, high current density sources are required to achieve the small beam size needed for high frequency vacuum electronic devices and for high power free electron lasers (FELs). Emission models are of particular importance in the emittance-dominated regime, where emission non-uniformity and surface structure of the cathode can have an impact on beam characteristics. We have been developing comprehensive time-dependent photoemission models for the simulation codes that account for laser and cathode material and surface characteristics. MICHELLE* is NRL's finite-element self-consistent electrostatic time-domain code: it has the ability to import an RF field, and has unique capabilities for modeling the emission and the self fields, near the cathode. In particular, some instances of surface irregularities and emission non-uniformity (due to work function variation) leading to such effects as beam emittance and high frequency oscillations are possible to model due to the code's conformal meshing capabilities. We will present results of the implementation of the 'next generation' photoemission models in the MICHELLE code for modeling surface roughness and non-uniformity.
* John Petillo, et al., "The MICHELLE Three-Dimensional Electron and Collector Modeling Tool: Theory and Design", IEEE Trans. Plasma Sci., vol. 30, no. 3, June 2002, pp. 1238-1264.
Fermilab, Batavia, Illinois
LBNL, Berkeley, California
SLAC, Menlo Park, California
Over the past years, SLAC's Advanced Computations Department (ACD) has developed the parallel finite element particle-in-cell code Pic3P (Pic2P) for simulations of beam-cavity interactions dominated by space-charge effects. As opposed to standard space-charge dominated beam transport codes, which are based on the electrostatic approximation, Pic3P (Pic2P) includes space-charge, retardation and boundary effects as it self-consistently solves the complete set of Maxwell-Lorentz equations using higher-order finite element methods on conformal meshes. Use of efficient, large-scale parallel processing allows for the modeling of photoinjectors with unprecedented accuracy, aiding the design and operation of the next-generation of accelerator facilities. Applications to the Linac Coherent Light Source (LCLS) RF gun are presented.
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
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.
INFN-Milano, Milano
INFN/LNF, Frascati (Roma)
INFN-Roma II, Roma
ENEA C. R. Frascati, Frascati (Roma)
Universita di Roma I La Sapienza, Roma
INFN-Milano, Milano
Universita degli Studi di Milano, Milano
INFN/LNF, Frascati (Roma)
INFN/LNF, Frascati (Roma)
INFN-Milano, Milano
INFN-Roma, Roma
ISSP/SRL, Chiba
* J. M. Wang and J. Wu, PRST-AB 7, 034402(2004)
USTC/NSRL, Hefei, Anhui
USTC, Hefei, Anhui
PAL, Pohang, Kyungbuk
TUB, Beijing
A high-brightness electron beam is emitted from a photo-cathode (PC) RF gun for use in the FIR (Far Infrared) facility being built at the Pohang Accelerator Laboratory (PAL). The beam dynamics study for the PAL XFEL injector is essencial to generate low emittance electron beam from the PC RF gun. The XFEL injector requires 1 nC beam with short bunch length and low emittance. This conditions are simulated with PARMELA code and then are realized on experimental conditions. The experimental conditions for the XFEL injector are measured with beam diagnostic devices such as ICT and Faraday cup for charge measurement, a spectrometer for beam energy measurement. In this article, we present the experimental approaches of the beam dynamics study for the XFEL injector.
wpjho@postech.ac.kr (Jangho Park)
ALBA, Bellaterra (Cerdanyola del Valles)
ANL, Argonne, Illinois
A high-resolution X-band cavity beam position monitor (BPM) has been developed for the LCLS in order to achieve micron-level accuracy of the beam position using a dipole mode cavity and a monopole mode reference cavity. The rf properties of the BPM will be discussed in this paper including output power, tuning, and issues of manufacturing. In addition, methods will be presented for improving the isolation of the output ports to differentiate between horizontal/vertical beam motion and to reject extraneous modes from affecting the output signal. The predicted simulation results will be compared to data collected from low-power experimental tests.
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
We plan to commission top-off injection at the Advanced Light Source in the near future. In order to guarantee radiation safety, we have been simulating the injection process to exclude the possibility of injected electrons traveling down the user's photon beam lines. As the final stage of our simulation study, we use photon beam line CAD drawings to define the beam line's aperture in the phase space which electrons must not enter. Then we virtually inject electrons from within these phase spaces backwards into the storage ring to prove that such electrons can never get back to the real injection point under any possible scenario. This paper summarizes such inverse tracking studies.
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.
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.
BNL, Upton, Long Island, New York
IUCF, Bloomington, Indiana
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.
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.
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
BESSY GmbH, Berlin
Rome University La Sapienza, Roma
A 2.1 GeV electron storage ring can serve as a third-generation light source for photon energies of 1-2000 eV. We design a ring with emittance of 1.5 nm-rad, circumference of 215 m, and twelve 5.5 m long straight sections. With a 100 MHz radiofrequency (rf) system, the computed Touschek current-lifetime product is 2800 mA-hr. Two passive fifth-harmonic cavities may be used to suppress parasitic coupled-bunch instabilities while increasing the bunchlength and lifetime by a factor of four. For stable operation with ring currents up to 600 mA, microwave-instability simulations indicate that the reduced longitudinal impedance should not exceed 1.5Ω.
* M. Borland, APS Report LS-287
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.
BNL, Upton, Long Island, New York
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
UMAN, Manchester
* C. Beard and R. M. Jones, EUROTeV-Report-2006-103** C. Beard and J. Smith, EPAC06 Proc. MOPLS070
CEA, Gif-sur-Yvette
GSI, Darmstadt
ORNL, Oak Ridge, Tennessee
The GSI UNILAC, a heavy ion linac originally dedicated for low current beam operation, together with the synchrotron SIS 18 will serve as an high current injector for FAIR (International Facility for Antiproton and Ion Research). The UNILAC post stripper accelerator consists of five Alvarez tanks with a final energy of 11.4 MeV/u. In order to meet the requirements of FAIR (15emA 238U28+, transverse normalised emittances of 0.8mm mrad and 2.5mm mrad) an UNILAC upgrade program is foreseen to increase the primary beam intensity as well as the beam brilliance. A detailed understanding of the beam dynamics during acceleration and transport of space charge dominated beams is necessary. For this purpose the study of the beam brilliance dependency on the phase advances in the Alvarez DTL is suited. Machine investigations were performed with various beam diagnostics devices established in the UNILAC. Measurements done in 2006 using an high intensity heavy ion beam coincide with the beam dynamics work package of the European JRA "High Intensity Pulsed Proton Injector" (HIPPI). Results of these measurements are presented as well as corresponding beam dynamics simulations.
GSI, Darmstadt
ITEP, Moscow
IAP, Frankfurt am Main
The FAIR facility, under development at GSI, needs a new dedicated proton injector for the production of intense antiprotons secondary beams. This injector will accelerate protons from 3 to 70 MeV at a current of 70 mA, and due to the high voltage gain and shunt impedance will be based on CH cavities powered by a 2.5 MW, 325 MHz klystron. An innovative coupling cell containing one drift tube of length N-beta λ was developed to combine multicell drift tube modules of the CH-type (H210 mode).. In order to study this innovative coupling mechanism a scaled model of the second resonator of GSI Proton injector is under production at IAP. The according full scale prototype, 3 meter long coupled X MV resonator from MeV to MeV is under construction and will be power tested with a 2.5 MW klystron at GSI at the end of 2008. This paper describes in detail the coupled structure together with a general overview of the R&D results achieved on the CH-DTL's cavity.
IAP, Frankfurt am Main
IAP, Frankfurt am Main
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.
INFN/LNF, Frascati (Roma)
INFN/LNF, Frascati (Roma)
INFN/LNF, Frascati (Roma)
BINP SB RAS, Novosibirsk
KEK, Ibaraki
JAEA/LINAC, Ibaraki-ken
JAEA, Ibaraki-ken
KEK, Ibaraki
KEK, Ibaraki
GUAS/AS, Ibaraki
Nippon Advanced Technology Co. Ltd., Ibaraki-prefecture
* E. Nakamura et al., in PAC07** K. Takayama et al., "Experimental Demonstration of the Induction Synchrotron" appeared in Phys. Rev. Lett. soon and in PAC07
KEK, Ibaraki
BINP SB RAS, Novosibirsk
For the KEKB Accelerator Group.
BNL, Upton, Long Island, New York
CERN, Geneva
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
JAEA, Ibaraki-ken
JAEA/LINAC, Ibaraki-ken
KAERI, Daejon
The 100 MeV Linac of the Proton Engineering Frontier Project (PEFP) consists of an ion source, a low energy beam transport (LEBT), a 3 MeV radio frequency quadrupole (RFQ), and an 100 MeV drift tube linac (DTL). The DTL is separated into two parts. The first part includes 4 tanks which accelerate 20 mA proton beams up to 20 MeV. The medium energy beam transport (MEBT) follows the 20 MeV accelerator in order to match proton beams into the next linac as well as to extract and supply 20 MeV proton beams to the user facilities. The second part of the DTL consists of 7 tanks to accelerate proton beams to 100 MeV. This work focuses on the error analysis of the designed 100 MeV linac in order to obtain the tolerance limit in the fabrication and alignment processes of the linac as well as to study the steering magnets which control the beam fluctuations and reduce the potential beam loss.
JINR, Dubna, Moscow Region
JINR, Dubna, Moscow Region
IBA, Louvain-la-Neuve
MEPhI, Moscow
* E. S. Masunov, Technical Physics, V. 46, 11, 2001, pp. 1433-1436.**E. S. Masunov, S. M. Polozov, NIM., A 558, 2006, pp. 184-187.
EPFL, Lausanne
CERN, Geneva
BNL, Upton, Long Island, New York
Fermilab, Batavia, Illinois
CERN, Geneva
CERN, Geneva
ORNL, Oak Ridge, Tennessee
CERN, Geneva
INFN/LNL, Legnaro, Padova
INFN-Milano, Milano
CERN, Geneva
CERN, Geneva
CERN, Geneva
CERN, Geneva
STFC/RAL/ISIS, Chilton, Didcot, Oxon
CERN, Geneva
CERN and RAL are working in parallel to develop Front Ends for future particle accelerators. At CERN the Front End will be part of LINAC4, a potential replacement for the Linac2 accelerator, whilst at RAL the Front End is intended to demonstrate that a high current, high quality chopped beam is achievable and that the design could be used as part of a Proton Driver for a future Neutrino Factory. The two Front End designs have many similarities and basically consist of four main components: an H- ion source, a Low Energy Beam Transport (LEBT) matching into a Radio-Frequency Quadrupole (RFQ) and a Medium Energy Beam Transport (MEBT) line with a fast beam chopper. The beam choppers are different in the two designs and it is important to compare the effectiveness of the two methods of operation. This paper describes a simulation study of high intensity beam dynamics and beam transport when the RAL and CERN MEBT designs are each fed into the same CERN structure for LINAC4.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
Imperial College of Science and Technology, Department of Physics, London
STFC/RAL/ISIS, Chilton, Didcot, Oxon
STFC/RAL, Chilton, Didcot, Oxon
ANL, Argonne, Illinois
The Advanced Exotic Beam Laboratory (AEBL) being developed at ANL consists of an 833 MV heavy-ion driver linac capable of producing uranium ions up to 200 MeV/u and protons to 580 MeV with 400 kW beam power. We have designed all accelerator components including a two charge state LEBT, an RFQ, a MEBT, a superconducting linac, a stripper section and beam switchyard. We present the results of an optimized linac design and end-to-end simulations which include possible machine errors.
ANL, Argonne, Illinois
The Intense Pulsed Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 3.2x 1012 protons from 50 MeV to 450 MeV at 30 Hz. During the 14.2 ms acceleration period, the RF frequency varies from 2.21 MHz to 5.14 MHz. In order to improve capture efficiency, we varied the injection timing and the early RF voltage profiles. The experimental results are compared with similar studies at ISIS and calculation done with the 1-D tracking code, Capture-SPC. This allowed us to optimize injection time and the RF voltage profile for better capture efficiency. An optimized injection time and RF voltage profile was found that resulted in raising the capture efficiency from 85.1% to 88.6%. These studies have now also been expanded to included 2nd harmonic RF during the capture and initial acceleration cycle in the RCS.
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
Two barrier rf systems were fabricated, tested and installed in the Fermilab Main Injector.* Each can provide 8-10 kV rectangular pulses (the rf barriers) at 90 kHz. When a stationary barrier is combined with a moving barrier, injected beams from the Booster can be continuously deflected, folded and stacked in the Main Injector (MI), which leads to doubling of the beam intensity. This paper gives a report on the beam experiment using this novel technology.
* W. Chou, D. Wildman and A. Takagi, "Induction Barrier RF and Applications in Main Injector," Fermilab-Conf-06-227 (2006).
Fermilab, Batavia, Illinois
KEK, Ibaraki
Fermilab, Batavia, Illinois
A 8 GeV H- superconducting linac has been proposed as an alternative injector for the Main Injector to support a 2 MW Neutrino program. An injection absorber is required to accept protons generated after the secondary stripping foil which will intercept the un-stripped H- and H0 particles after the MI primary foil injection point. The motivations underlying the choice of a compact internal absorber over an external absorber will be discussed. We show that using a high-Z material (tungsten) for the inner shielding allows the construction a compact absorber that can take a very intense beam and fits within the existing enclosure. The absorber requirements and a shielding design and the results of energy deposition calculations are presented.
BNL, Upton, Long Island, New York
The technique for H- charge exchange for multi-turn injection utilizing stripping foils in the energy range of a few hundred MeV has been used at many labs for decades and most recently up to 1 GeV at the SNS. Utilization the beam from the proposed Proton Driver* would permit the extension of this technique up to 8 GeV. The injection layout and required accelerator modifications are discussed. Results from transverse and longitudinal simulations are presented.
* W. G. Foster and J. A. MacLachlan, "A Multi-mission 8 GeV Injector Linac as a Fermilab Booster Replacement", Proc. Of LINAC-2002, Gyeongju, Korea, p.86.
Fermilab, Batavia, Illinois
BINP SB RAS, Novosibirsk
Fermilab, Batavia, Illinois
IUCF, Bloomington, Indiana
The Low Energy Neutron Source (LENS) at Indiana University is producing neutrons by using a 7 MeV proton beam incident on a Beryllium target. The Proton Delivery System is currently being upgraded. A new DTL section will be added to increase proton beam energy from 7 to 13 MeV. A 3 MeV RFQ and 13 MeV DTL will be powered by 1 MW klystrons. The goal of this upgrade is a 13 MeV, 20 mA proton beam with duty factor more than 1%. At this power level it becomes increasingly important to make a proton beam that is uniformly distributed to prevent excessive thermal stress at the surface of the Be target. To achieve this goal two octupole magnets are being implemented in the LENS beam transport line. In this paper we discuss the experimental results of the beam intensity redistribution as well as some features inherent in tuning of the nonlinear beamline and our operational experience.
Texas A&M University, College Station, Texas
A conceptual design is presented for the 50 Tesla superconducting solenoids that are required for an optimized fast cooling ring in current designs for multi-TeV muon colliders. The solenoid utilizes high-performance multi-filament Bi-2212/Ag round strand. The conductor is a cable-in-conduit consisting of six such strands cabled around a thin-wall spring tube then drawn within an outer sheath. The spring tube and the sheath are made from high-strength superalloy Inconel. The solenoid coil comprises 5 concentric shells supported independently in the conventional manner. Each shell consists of a winding of the structured cable, impregnated in the voids between cables but empty inside so that the spring tubes decouple stress so that it cannot strain-degrade the fragile strands, and a high-modulus overband. An expansion bladder is located between the winding and the overband, and is pressurized and then frozen to provide hydraulic compressive preload to each shell. This approach makes it possible to accommodate ~10 T field contribution from each shell without degradation, and provides distributed refrigeration so that heat is removed throughout the windings.
ORNL, Oak Ridge, Tennessee
NSCL, East Lansing, Michigan
In supporting pre-conceptual research and development of the Rare-Isotope Accelerator facility or similar next-generation exotic beam facilities, one critical focus area is to estimate the level of activation and radiation in the linear accelerator second stripping region and to determine if remote handling is necessary in this area. A basic geometric layout of the second stripping region having beamline magnets, beam pipes and boxes, a stripper foil, beam slits, and surrounding concrete shielding was constructed for Monte Carlo simulations. Beam characteristics were provided within the stripping region based on this layout. Radiation fields, radioactive inventories, levels of activation, heat loads on surrounding components, and prompt and delayed radiation dose rates were simulated using Monte-Carlo radiation transport code PHITS. Preliminary results from simulations using a simplified geometry show that remote handling of foils and slits will be necessary. Simulations using a realistic geometry are underway and the results will be presented.
NSCL, East Lansing, Michigan
To support pre-conceptual research and development for rare isotope beam production via projectile fragmentation at the Rare-Isotope Accelerator facility or similar next-generation exotic beam facilities, the interactions between primary beams and beryllium and liquid-lithium production targets in the fragment pre-separator area were simulated using the Monte-Carlo radiation transport code PHITS. The purpose of this simulation is to determine the magnitude of the radiation fields in the pre-separator area so that levels of hadron flux and energy deposition can be obtained. It was of particular interest to estimate the maximum radiation doses to magnet coils and other components such as the electromagnetic pump for a liquid-lithium loop, and to estimate component lifetimes. We will show a detailed geometry of the pre-separator area developed for these simulations. We will provide verification that trajectories of beams and fragments when transported in the PHITS simulations agree with results from standard ion-optics calculations. We will present estimates of radiation doses to pre-separator components and give estimates for component lifetimes.
NSCL, East Lansing, Michigan
Rare Isotope Beams (RIBs) are created at the National Superconducting Cyclotron Laboratory (NSCL) by the in-flight particle fragmentation method. A novel system is proposed to stop the RIBS in a helium filled gas system followed by reacceleration that will provide opportunities for an experimental program ranging from low-energy Coulomb excitation to transfer reaction studies of astrophysical reactions. The beam from the gas stopper will first be brought into a Electron Beam Ion Trap (EBIT) charge breeder on a high voltage platform to increase its charge state and then accelerated initially up to about 3 MeV/u by a system consisting of an external multi-harmonic buncher and a radio frequency quadrupole (RFQ) followed a superconducting linac. The superconducting linac will use quarter-wave resonators with bopt of 0.047 and 0.085 for acceleration and superconducting solenoid magnets for transverse focusing. The paper will discuss the accelerator system design and present the end-to-end beam dynamics simulations.
NSCL, East Lansing, Michigan
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.
LLNL, Livermore, California
Proton accelerator structures for medical applications using Dielectric Wall Accelerator (DWA) technology allows for the utilization of high field gradients on the order of 100 MV/m to accelerate the proton bunch. Medical applications involving cancer therapy treatment usually desire short bunch lengths on the order of hundreds of picoseconds in order to limit the extent of the energy deposited in the tumor site (in 3D space, time, and deposited proton charge). Electromagnetic simulations of the DWA structure, in combination with injections of proton bunches, have been performed using 3D finite difference codes in combination with particle pushing codes. Electromagnetic simulations of DWA structures includes these effects and also includes the details of the switch configuration and how that switch time affects the electric field pulse which accelerates the particle beam. Design trade-offs include the driving switch effects, layer-to-layer coupling analysis and its affect on the pulse rise time.
LLNL, Livermore, California
An investigation is being made into the feasibility of making a compact proton accelerator for medical radiation treatment. The accelerator is based on high gradient insulation (HGI) technology. The beam energy should be tunable between 70 and 250 MeV to allow the Bragg peak to address tumors at different depths in the patient. The desired radiation dose is consistent with a beam charge of 40 pico-coulombs. The particle source is a small 2 mm plasma device from which a several nano-second pulse can be extracted. The beam current is selectable by the potential of the extraction electrode and is adjustable in the range of 10-100 milli-Amperes. This beam is then accelerated and focused by the next three electrodes forming a Accel-Deaccel-Accel (ADA) structure leading to the DWA accelerator block. The spot size is adjustable over 2 to 10 mm. A transparent grid terminates the injector section and prevents the very high gradient of the HGI structure from influencing the overall focusing of the system. The beam energy is determined by the length of the DWA structure that is charged. This give independent selection of beam dose, size and energy.
LLNL, Livermore, California
The dielectric wall accelerator (DWA) is a compact induction accelerator structure that incorporates the accelerating mechanism, pulse forming structure, and switch structure into an integrated module. The DWA consists of stacked stripline Blumlein assemblies, which can provide accelerating gradients in excess of 100 MeV/meter. Blumleins are switched sequentially according to a prescribed acceleration schedule to maintain synchronism with the proton bunch as it accelerates. A finite difference time domain code (FDTD) is used to determine the applied acceleration field to the proton bunch. Particle simulations are used to model the injector as well as the accelerator stack to determine the proton bunch energy distribution, both longitudinal and transverse dynamic focusing, and emittance associated with various DWA configurations.
LLNL, Livermore, California
A compact proton accelerator for medical applications is being developed at Lawrence Livermore National Laboratory. The accelerator architecture is based on the dielectric wall accelerator (DWA) concept. One critical area to consider is the switch region. Electromagnetic field simulations and thermal calculations of the switch area were performed to help determine the operating limits of the SiC switches. Different geometries were considered for the field simulation including the shape of the thin indium solder meniscus between the electrodes and SiC, and possible misalignment of electrodes and SiC during manufacturing. Electromagnetic field simulations were also utilized to demonstrate how the field stress could be reduced. Both transient and steady-state thermal simulations were analyzed to find the average power capability of the switches.
LANL, Los Alamos, New Mexico
The LANSCE linac simultaneously provides both H+ and H- beams to several user facilities. The Weapons Neutron Research (WNR) user facility is configured to accept the H- beam with a typical pulse pattern of one linac micro-pulse every 1.8 microseconds. To produce this pulse spacing a slow-wave chopper located in the 750 keV injector beam transport is employed to intensity modulate the beam. The beam is subsequently bunched at both 16.77 MHz and 201.25 MHz prior to entering the 100 MeV drift tube linac. One downside of the chopping process is that the majority of the beam produced by the ion source during the WNR macro-pulses is discarded. By applying a longitudinal bunching action immediately following the ion source, simulations have shown that some of this discarded beam can be used to increase the charge in these micro-pulses. Recently, we began an effort to develop this buncher by superimposing 16.77 MHz RF voltage on one of the HVDC electrodes in the 80 kV column located inside H- Cockcroft-Walton dome. This paper describes the beam dynamics simulations, design and implementation of the rf hardware and the results of tests performed with the system.
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
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.
* J. D. Sherman, these conference proceedings.
BNL, Upton, Long Island, New York
Full spin flip in the presence of full Siberian snake has been achieved by using an rf dipole or solenoid as spin flipper at IUCF and COSY. This technique requires one to change the snake configuration to move the spin tune away from half integer. However, this is not practical for an operational high energy polarized proton collider like RHIC where beam lifetime is sensitive to small betatron tune change. An new technique of achieving full spin flip with the spin tune staying at half integer is proposed. This paper presents the design of RHIC spin flipper along with simulation results.
KEK, Ibaraki
CERN, Geneva
A small angle (< 1mrad) crab scheme is an attractive option for the LHC luminosity upgrade to recover the geometric luminosity loss from the finite crossing angle, which steeply increases to unacceptable levels as the IP beta function is reduced below its nominal value. The crab compensation in the LHC can be accomplished using only two sets of deflecting rf cavities, placed in collision-free straight sections of LHC to nullify the crossing angles at IP1 & IP5. We present IR optics configurations with low-angle crab crossing, study the beam-beam performance and proton-beam emittance growth in the presence of crab compensation, lattice errors, crab RF noise sources. We also explore a 400MHz superconducting cavity design and discuss the pertinent RF challenges.
BNL, Upton, Long Island, New York
CERN, Geneva
We use transverse beam transfer functions to measure tune distributions of colliding beams in RHIC. The tune has a distribution due to the beam-beam interaction, nonlinear magnetic fields – particularly in the interaction region magnets, and non-zero chromaticity in conjunction with momentum spread. The measured tune distributions are compared with calculations.
BNL, Upton, Long Island, New York
CERN, Geneva
SLAC, Menlo Park, California
Fermilab, Batavia, Illinois
LBNL, Berkeley, California
A DC wire has been installed in RHIC to explore the long-range beam-beam effect, and test its compensation. We report on experiments that measure the effect of the wire's electro-magnetic field on the beam's lifetime and tune distribution, and accompanying simulations.
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
IAP, Frankfurt am Main
The EBIS (Electron Beam Ion Source) Project at Brookhaven National Laboratory is in the second year of a four-year project. It will replace the Tandem Van de Graaff accelerators with an EBIS, an RFQ, and one IH Linac cavity as the heavy ion preinjector for the Relativistic Heavy Ion Collider (RHIC), and for the NASA Space Radiation Laboratory (NSRL). The preinjector will provide all ions species, He to U, (Q/m>0.16) at 2 MeV/amu at a repetition rate of 5 Hz, pulse length of 10–40 μs, and intensities of ~2.0 mA. End-to-end simulations (from EBIS to the Booster injection) as well as error sensitivity studies will be presented and physics issues will be discussed.
#Raparia@bnl.gov
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.
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)
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
Fermilab, Batavia, Illinois
The International Linear Collider will be the largest most complicated accelerator ever built. For this reason extensive work is being done early in the design phase to ensure that it will be reliable enough. This includes gathering failure mode data from existing accelerators and simulating the failures and repair times of the ILC. This simulation has been written in a general fashion using MATLAB and could be used for other accelerators. Results from the simulation tool have been used in making some of the major ILC design decisions and an unavailability budget has been developed.
Eisenwerke Fried. Wilh. Dueker GmbH & Co. KGaA, Laufach
Clausthal, Inst für Nichtmetall. Werkstoffe, Clausthal-Zellerfeld
CERN, Geneva
Wendel GmbH, Dillenburg
DESY, Hamburg
BNL, Upton, Long Island, New York
Stochastic cooling of 100 GeV/nucleon bunched beams has been achieved in the Relativistic Heavy Ion Collider (RHIC). The physics and technology of the longitudinal cooling system are discussed, and plans for a transverse cooling system are outlined.
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.
LLNL, Livermore, California
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
Intense heavy ion beam pulses need to be compressed in both the transverse and longitudinal directions for warm dense matter and heavy ion fusion applications. Previous experiments and simulations utilized a drift region filled with high-density plasma in order to neutralize the space-charge and current of a 300 keV K+ beam, and achieved transverse and longitudinal focusing separately to a radius < 2 mm and pulse width < 5 ns, respectively. To achieve simultaneous beam compression, a strong solenoid is employed near the end of the drift region in order to transversely focus the beam to the longitudinal focal plane. Simulations of near-term experiments predict that the ion beam can be focused to a sub-mm spot size coincident with the longitudinal focal plane, reaching a peak beam density in the range 1012 - 1013 cm-3, provided that the plasma density is large enough for adequate neutralization. Optimizing the compression under the appropriate experimental constraints offers the potential of delivering higher intensity per unit length of accelerator to the target, thereby allowing more compact and cost-effective accelerators and transport lines to be used as ion beam drivers.
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.
IAP, Frankfurt am Main
The superconducting CH-structure is the first multi-cell cavity for the acceleration of low and medium energy ions and protons. A superconducting prototype cavity has been built and several cold tests have been performed at the IAP in Frankfurt. After the detection of a field emission centre the cavity will be treated by buffered chemical polishing and high pressure rinsing. Additionally the cavity is being prepared for tests in a horizontal cryostat with slow and fast tuner system. We present the status of these developments and the test results which have been gained recently.
DESY, Hamburg
Measurements of effective Radio Frequency (RF) field parameters (amplitude and phase) are tasks of great importance in high-energy accelerators*. The RF signal is downconverted in frequency to intermediate frequency (IF) but keeping the information about amplitude and phase. The IF signal is then sampled in ADC and processed in digital IQ detector computing the I and Q components**. The downconverter is a nonlinear device thus not only the fundamental frequency but also its harmonics are present and sampled by ADC. For a typical downconverter (used in FLASH LLRF system) the higher order harmonics levels depend on RF signal level and are about 40dBm lower than the fundamental frequency component. These harmonics can produce errors in IQ detector of up to few percent in amplitude and few degree in phase. These errors depends not only on nonlinearity of downconverter but also on the IQ detection scheme*** (IF and sampling rate SR). The paper presents the optimization of the IQ detection scheme (choosing the IF and SR) taking into account the nonlinear characteristics of the downconverter.
*Grelick A. et all:A High-Resolution…, Proc. LINAC 2004,715-718**Grecki M. et all:Estimation of IQ…, Proc. MIXDES 2005,783-788***Simrock S. et all:Considerations…, Proc. EPAC 2006,1462-1464
INFN/LASA, Segrate (MI)
TETD, Otawara
Toshiba, Yokohama
KEK, Ibaraki
IHEP Beijing, Beijing
TUL-DMCS, Lodz
DESY, Hamburg
INFN/LASA, Segrate (MI)
The SC cavities need a fast tuning system, which is able to adjust the shape during the pulse operation. The first attempts were focused on the compensation of the repetitive and periodic distortion. The algorithms were implemented in Matlab and allow compensating only the Lorentz force detuning. However, the previous solution was too slow to be able to compensate the microphonics. The paper presents recent development in the field. The previously worked out algorithms are implemented in the FPGA-based control system. The SIMCON board is used, which allows to perform parallel, deeply pipelined calculation. The new approach allows integrating the algorithm dedicated for cavity shape control with the LLRF system used for vector sum control. Moreover, the new algorithm for on-line detuning calculation which base on the electromechanical model of the cavity is presented. The system is tested with Module Test Stand (MTS) at DESY with the high gradient cavities (37 MV/m). The active elements are the NOLIAC's and PI's multilayer, low voltage piezostacks. The paper will present the first results from these measurements.
KAERI, Daejon
A new type of coaxial higher-order mode (HOM) coupler with one hook and two stubs has been designed for PEFP SRF cavities to satisfy the HOM damping requirements of the superconducting RF (SRF) linac of the Proton Engineering Frontier Project (PEFP), and to overcome the notch frequency shift and feed-through tip melting issues. This paper has presents details on the PEFP HOM coupler?s structure, structure optimization, filter characteristics, electro-magnetic field distribution and a coupler installation tool.
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.
KAERI, Daejon
The RF amplitude and the phase stability requirements of the LLRF system for the PEFP(Proton Engineering Frontier Project) proton linac are within 1% and 1 degree, respectively. As a prototype of the LLRF, a simple digital PI control system based on commercial FPGA board is designed and tested. The main features are a sampling rate of 40 MHz which is four times higher than the down-converted cavity signal frequency, digital in-phase and quadrature detection, pulsed mode operation with the external trigger, and a simple proportional-integral feedback algorithm implemented in a FPGA. The developed system was tested with 3 MeV RFQ and 20 MeV DTL, and satisfied the stability requirements.
KAERI, Daejon
PAL, Pohang, Kyungbuk
The temperature-controlled cooling water system was designed to obtain the resonance frequency stabilization of the normal conducting drift tube linac (DTL) for the PEFP 100 MeV proton accelerator. The primary sizing of individual closed-loop low conductivity cooling water pumping skids for each DTL system was conducted with a simulation of thermo-hydraulic network model. The temperature control schemes incorporating the process dynamic model of heat exchangers were examined to regulate the input water temperatures into the DTL during the steady state operation. The closed water circuits to achieve system performance and stability for low and full duty operation modes were discussed, and numerical results were also presented.
TRIUMF, Vancouver
The present AGS injection kickers at A5 location were designed for 1.5 GeV proton injection. Recent high intensity runs have pushed the transfer kinetic energy to 1.94 GeV, but with an imperfect matching in transverse phase space. Space charge forces result in both fast and slow beam size growth and beam loss as the size exceeds the AGS aperture. An increase in the AGS injection energy to 2 GeV with adequate kick strength would greatly reduce the beam losses making it possible to increase the intensity from 70 TP (70 * 1012 protons/s) to 100 TP. R&D studies* have been undertaken by TRIUMF, in collaboration with BNL, to design two new kicker magnets for the AGS A10 location to provide an additional kick of 1.5 mrad to 2 GeV protons. TRIUMF has designed and built a prototype 12.5 Ω transmission line kicker magnet with rise and fall times of 100 ns, 3% to 97% and field uniformity of (±)1% over 85% of the aperture, powered by matched 12.5 Ω pulse-forming lines. This paper describes the results of detailed capacitance and inductance measurements, on the prototype magnet, and compares these with predictions from 2D and 3D electromagnetic simulations.
*L. Ahrens, R. B. Armenta, M. J. Barnes, E. W Blackmore, C. J. Gardner, O. Hadary, G. D. Wait, W. Zhang, "Design Concept for AGS Injection Kicker Upgrade to 2 GeV", PAC 2005, Knoxville Tennessee.
CERN, Geneva
Thomson Broadcast & Multimedia AG, Turgi
Thomson Broadcast & Multimedia has been awarded a contract from DESY to design and build a prototype klystron modulator for the XFEL project. This modulator will be built in pulse step modulator (PSM) technology. This technology will allow to control the pulse form to achieve a maximum flatness of the pulse without tuning any high power components. The modulator will also have a built-in power regulation to prevent voltage flicker of the mains. The paper will give an overview about the principles of the modulator and presents the status of the design. It also shows simulation results about the expected performance.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Cockcroft Institute, Lancaster University, Lancaster
UMAN, Manchester
Cockcroft Institute, Warrington, Cheshire
In order to verify detailed impedance simulations, the modes in an aluminium model of the ILC crab cavity were investigated using a bead-pulling technique as well as a stretched-wire frequency domain measurement. The combination of these techniques allow for a comprehensive study of the modes of interest. For the wire measurement, a transverse alignment system was fabricated and rf components were carefully designed to minimize any potential impedance mismatches. The measurements are compared with direct simulations of the stretched-wire experiments using numerical electromagnetic field codes. High impedance modes of particular relevance to the ILC crab cavity are identified and characterized
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Fermilab, Batavia, Illinois
Cockcroft Institute, Lancaster University, Lancaster
The ILC crab cavity will require the design of an appropriate power coupler. The beamloading in dipole cavities is considerably more variable than accelerating cavities, hence simulations have been performed to establish the required external Q. Simulations of a suitable coupler were then performed and were verified using a normal conducting prototype with variable coupler tips.
Cockcroft Institute, Warrington, Cheshire
ANL, Argonne, Illinois
High-power tests were conducted on a 350MHz, single-cell copper accelerating cavity driven simultaneously by two H-loop input couplers for the purpose of determining the reliability, performance, and power-handling capability of the cavity and related components, which have routinely operated at 100kW power levels. The test was carried out utilizing the APS 350MHz RF Test Stand, which was modified to split the input rf power into two 1/2-power feeds, each supplying power to a separate H-loop coupler on the cavity. Electromagnetic simulations of the two-coupler feed system were used to determine coupler match, peak cavity fields, and the effect of phasing errors between the coupler feedlines. The test was conducted up to a maximum total rf input power to the cavity of 200kW CW. Test apparatus details and performance data will be presented.
ANL, Argonne, Illinois
INFN/LNL, Legnaro, Padova
This paper reports the development of a 5-10 kW cw variable coupler for 345 MHz spoke-loaded superconducting (SC)cavities. The coupler inserts an 80K copper loop into a 5 cm diameter coupling port on several types of spoke-loaded cavity operating at 2 - 4K. The coupling loop can be moved during operation to vary the coupling over a range of 40 dB. The coupler is designed to facilitate high-pressure water rinsing and low-particulate clean assembly. Design details and operating characteristics are discussed.
ANL, Argonne, Illinois
The Argonne Tandem Linear Accelerator System (ATLAS) is the first superconducting heavy-ion linac in the world. Currently ATLAS is being upgraded with the Californium Rare Ion Breeder Upgrade (CARIBU). The latter is a funded project to expand the range of short-lived, neutron-rich rare isotope beams available for nuclear physics research at ATLAS. To avoid beam losses associated with the existing gridded multi-harmonic buncher, we have developed and built a grid-less four-harmonic buncher with fundamental frequency of 12.125 MHz. In this paper, we are going to report the ATLAS beam performance with the new buncher.
STAR, Inc., Mequon, Wisconsin
Fermilab, Batavia, Illinois
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.
Fermilab, Batavia, Illinois
Operated by Universities Research Association, Inc., under Contract No. DE-AC02-76CH03000 with the U. S. Department of Energy#mcgee@fnal.gov
Fermilab, Batavia, Illinois
The technology for mechanically compensating Lorentz Force detuning in superconducting RF cavities has already been developed at DESY. One technique is based on commercial piezoelectric actuators and was successfully demonstrated on TESLA cavities*. Piezo actuators for fast tuners can operate in a frequency range up to several kHz; however, it is very important to maintain a constant preload force on the piezo stack in the range of 10 to 50% of its specified blocking force. Determining the preload force during cooldown, warm-up, or re-tuning of the cavity is difficult without instrumentation, and exceeding the specified range can permanently damage the piezo stack. A technique based on strain gauge technology for superconducting magnets has been applied to fast tuners for monitoring the preload on the piezoelectric assembly. This paper will address the design and testing of piezo actuator preload sensor technology. Results from measurements of preload sensors installed on the tuner of the DESY Capture Cavity II tested at Fermilab will be presented. These results include measurements during cooldown, warm-up, and cavity tuning along with dynamic Lorentz force compensation.
* M. Liepe et al," Dynamic Lorentz Force Compensation with a Fast Piezoelectric Tuner" PAC2001
Fermilab, Batavia, Illinois
DESY, Hamburg
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.
MIT/PSFC, Cambridge, Massachusetts
A photonic band gap (PBG) higher-order-mode (HOM) coupler is proposed as an Alternative Configuration Design (ACD) for the HOM coupler for the International Linear Collider (ILC). The PBG HOM coupler uses a two-dimensional triangular PBG structure with good axial symmetry. Simulation studies of a PBG HOM coupler show that it maintains the operating mode at 1.3 GHz with . While a PBG HOM coupler provides superior damping for all the higher order modes in principle, detailed studies of the effectiveness of HOM damping are being carried out, and results 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.
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
AES, Medford, NY
An experiment has been conducted to measure small differences in cavity Q caused by various cavity surface treatments. A requirement of the experiment was that it show little sensitivity to the reassembly with various test pieces. We chose a coaxial half-wave resonator, with an outer conductor extending significantly beyond the length of the inner conductor. The outer conductor acts as a cut-off tube, eliminating the need for electric termination and thus any RF-contacts that can influence the Q-measurements. The experiment is aimed at qualifying the performance of cyanide-copper plated GlidCop in comparison with that of a machined GlidCop surface. To maximize the sensitivity of the measurement we use a fixed outer conductor made of annealed OFE copper and only replace the inner conductor, which is mounted on a low-loss Teflon pedestal located in the low electric field region. The Q-values of machined GlidCop and cyanide-copper plated GlidCop inner conductors are measured against the reference Q of the annealed OFE co-axial cavity. This simple configuration allows a statistically significant number of repetitions of measurements and should provide accurate comparative measurements.
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
Rome University La Sapienza, Roma
The hybrid photoinjector is a high current, low emittance photoinjector/accelerator and is under design and collaboration at Roma University La Sapienza, INFN - Laboratori Nazionali di Frascati and the UCLA Particle Beam Physics Lab. The hybrid standing wave-traveling wave photoinjector uses a coupling cell to divide power between a high-field 1.6 cell standing wave photoinjector, for electron emission and collection, and a low power traveling wave accelerator, for acceleration to desired energies at low emittances. Simulation results show promising beam properties of less than 4 mm-mrad emittance, energy spreads of 1.5%, and currents as high as 1.2 kA at energies of 21 MeV. We report on the progress of RF design and results of cold test RF measurements at the UCLA Pegasus Laboratory, including methods for measurements and difficulties arising in the transition from simulation to physical measurements.
SLAC, Menlo Park, California
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.
SLAC, Menlo Park, California
KEK, Ibaraki
Jefferson Lab, Newport News, Virginia
DESY, Hamburg
The Low-Loss shape cavity design has been proposed as a possible alternative to the baseline TESLA cavity design for the ILC. The advantages of this design over the TESLA cavity are its lower cryogenic loss, and higher achievable gradient due to lower surface fields. High gradient prototypes for such designs have been tested at KEK (ICHIRO) and JLab (LL). However, issues related to HOM damping and multipacting (MP) still need to be addressed. Preliminary numerical studies of the prototype cavities have shown unacceptable damping for some higher-order dipole modes if the typical TESLA HOM couplers are directly adapted to the design. The resulting wakefield will dilute the beam emittance thus reduces the machine luminosity. Furthermore, high gradient tests on a 9-cell prototype at KEK have experienced MP barriers although a single LL cell had achieved a high gradient. From simulations, MP activities are found to occur in the end-groups of the cavity. In this paper, we will present the optimization results of the end-groups for the Low-Loss shape for effective HOM damping and alleviation of multipacting. Comparisons of simulation results with measurements will also be presented.
SLAC, Menlo Park, California
Several high-current accelerators use feedback techniques in the accelerating RF systems to control the impedances seen by the circulating beam. These Direct and Comb Loop architectures put the high power klystron and LLRF signal processing components inside feedback loops, and the ultimate behavior of the systems depends on the individual sub-component properties. Imperfections and non-idealities in the signal processing leads to reduced effectiveness in the impedance controlled loops. In the PEP-II LLRF systems non-linear effects have been shown to reduce the achievable beam currents, increase low-mode longitudinal growth rates and reduce the margins and stability of the LLRF control loops. We present measurements of the driver amplifiers used in the PEP-II systems, and present measurement techniques needed to quantify the small-signal gain, linearity, transient response and image frequency generation of these amplifiers. Results are presented from measurements of 5 different types of amplifiers, and the trade-offs in selecting between them highlighted.
Fermilab, Batavia, Illinois
Cockcroft Institute, Lancaster University, Lancaster
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
SLAC, Menlo Park, California
The FNAL 9-cell 3.9GHz deflecting cavity designed for the CKM experiment was chosen as the baseline design for the ILC BDS crab cavity. Effective damping is required for the lower-order TM01 modes (LOM), the same-order TM11 modes (SOM) as well as the HOM modes to minimize the beam loading and beam centroid steering due to wakefields. Simulation results of the original CKM design using the eigensolver Omega3P showed that both the notch filters of the HOM/LOM couplers are very sensitive to the notch gap, and the damping of the unwanted modes is suboptimal for the ILC. To meet the ILC requirements, the couplers were redesigned to improve the damping and tuning sensitivity. With the new design, the damping of the LOM/SOM/HOM modes is significantly improved, the sensitivity of the notch filter for the HOM coupler is reduced by one order of magnitude and appears mechanically feasible, and the LOM coupler is simplified by aligning it on the same plane as the SOM coupler and by eliminating the notch filter. In this paper, we will present the coupler optimization and tolerance studies for the crab cavity.
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
JLAB, Newport News, Virginia
We describe the developments underway at JLab to develop new CW cryomodules capable of transporting up to Ampere-levels of beam currents for use in ERLs and FELs. Goals include an efficient cell shape, high packing factor for efficient real-estate gradient and very strong HOM damping to push BBU thresholds up by two or more orders of magnitude compared to existing designs. Cavity shape, HOM damping and ancillary components are optimized for this application. Designs are being developed for low-frequency (750 MHz), Ampere-class compact FELs and for high-frequency (1.5 GHz), 100 mA configurations. These designs and concepts can easily be scaled to other frequencies. We present the results of conceptual design studies, simulations and prototype measurements. These modules are being developed for the next generation ERL based high power FELs but may be useful for other applications such as high energy light sources, electron cooling, electron-ion colliders, industrial processing etc.
JLAB, Newport News, Virginia
Jefferson Lab, Newport News, Virginia
After initial cavity shape optimization* and cryomodule development** for an Ampere-class FEL, we have simulated the whole 5-cell high-current (HC) cavity structure with six waveguide couplers for HOM damping and fundamental power coupling. The time-domain wakefield method using MAFIA is primarily used for calculation of the broadband impedance. Microwave Studio and Omega-3P are also used for the calculation of external Q (Qext) of individual HOMs. A half scale (1497MHz) single-cell model and a 5-cell copper cavity including dummy HOM waveguide loads were fabricated. Details of measurement results on these prototypes including HOM Qext spectrum, bead-pull data, data analysis technique and comparison to the simulations will be presented.
* H. Wang et. al., "Elliptical Cavity Shape Optimization for Acceleration and HOM Damping," Proc. PAC 05, Knoxville TN, USA, 2005* R. A.Rimmer et al.; EPAC 2006, paper MOPCH182
ORNL, Oak Ridge, Tennessee
High power vector modulators can allow a fan-out RF power distribution system that can power many accelerating cavities from a single high-power klystron amplifier. The configuration enables independent control of amplitudes and phases of RF voltages at the cavities. A vector modulator employs either one or two hybrids with two fast phase shifters. Prototype high power RF vector modulators employing a hybrid and two fast ferrite phase shifters in coaxial TEM transmission lines for 402.5 MHz and 805 MHz are built and tested. RF properties of the design and result of high power testing are presented.
ORNL, Oak Ridge, Tennessee
Beam phase measurement based on detection of transient beam loading signal in a Superconducting (SC) cavity is utilized to setup the cavity synchronous phase. It has the potential to become a fast tune-up technique for a high intensity SC electron linac, as cavity phase could be determined precisely with only a few beam pulses. The paper introduces a transient detector study in the Spallation Neutron Source (SNS) proton linac, and discusses one of the major challenges - stochastic noise in the cavity RF system, which deteriorates the precision and increases the time needed for phase measurement with this technique. We analyze the influence of RF noise to the phase measurement in a simulation study with a beam-cavity model. Beam signal measurement with the cavity Low Level RF (LLRF) system and the initial experiment of prototype detectors are briefly introduced.
ORNL, Oak Ridge, Tennessee
A simulation code has been developed for the study of the Spallation Neutron Source (SNS) ring RF control. The code uses the time-domain solvers to compute beam-cavity interactions, and FFT methods to simulate time responses of the linear RF system. The important ingredients of the system are considered in the simulation model, which include the beam loading, dynamic cavity detuning, circuit bandwidth, loop delay, proportional-integral (P-I) controller for feedback and adaptive feed forward, stochastic noise, with-in-turn RF parameter change, beam current fluctuation and beam bunch leakage, etc. The beam loss in the accumulation ring goes up as the beam power increases, and thus a precise control of bunching voltage phase and amplitude is required to limit beam loss. This simulation tool will help the development a correct RF control and to achieve the goal of minimizing the beam loss.
TRIUMF, Vancouver
Fermilab, Batavia, Illinois
University of Pennsylvania, Philadelphia, Pennsylvania
http://einstein.hep.upenn.edu/~keungj/simulation.html
FAR-TECH, Inc. is developing and building a 36 kV, 830 kW klystron for the International Linear Collider (ILC) testing program. A variant of the tube can also be used to supply RF energy for a 2-3 meter section of ILC. The tube design is of the multiple-beam klystron (MBK) type, using ten beams with confined flow focusing. The design optimizes small tube size and low cost. The initial prototype will use an electromagnet, but the design allows for the eventual use of a permanent magnet solenoid. An efficiency of 65% is expected. We will present the design and status of the construction of the klystron and supporting systems.
ANL, Argonne, Illinois
Euclid TechLabs, LLC, Solon, Ohio
KEK, Ibaraki
Euclid TechLabs, LLC, Solon, Ohio
ANL, Argonne, Illinois
KEK, Ibaraki
Fermilab, Batavia, Illinois
Omega-P, Inc., New Haven, Connecticut
We describe a conceptual design for a superconducting traveling wave accelerator for the ILC. The RF feedback system plus phase shifter can redirect the accelerating wave that passed through the STWA section back to the input of the accelerating structure. In this paper, the STWA cell shape optimization, coupler cell design and rat race ring coupler in the feedback loop are presented. The STWA cell shape is similar to the LL cavity with a 60 mm disk diameter. A 9-cell STWA operates at the mode with group velocity as low as 0.0106 c. Both the ratio of peak electric field and magnetic field to the axial electric field are smaller than in the TESLA 9-cell cavity. The STWA structure has more cells per unit length than a TESLA structure but provides an accelerating gradient higher than a TESLA structure, consequently reducing the cost. The designed rat race directional coupler with four ports has ?3 dB direct coupling coefficients, 16.5 MHz bandwidth between ?30 dB isolations and 1.1 MHz bandwidth between ?30 dB reflection coefficients. Effects of the mechanical tolerances are also discussed.
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
We have recently developed a simplified model and a set of simple formulas for inductive voltage adder design. This model reveals the relationship of output waveform parameters and hardware designs. A computer simulation has demonstrated that parameter estimation based on this approach is accurate as compared to an actual circuit. This approach can be used in early stages of project development to assist feasibility study, geometry selection in engineering design, and parameter selection of critical components. In this paper, we give the deduction of a simplified model. Among the estimation formulas we present are those for pulse rise time, system impedance, and number of stages. Examples are used to illustrate the advantage of this approach. This approach is also applicable to induction LINAC design.
KEK, Ibaraki
KEK, Ibaraki
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.
KEK, Ibaraki
Nichicon (Kusatsu) Corporation, Shiga
IFIC, Valencia
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
LAL, Orsay
CEA, Gif-sur-Yvette
LAL, Orsay
IFIC, Valencia
LAL, Orsay
CERN, Geneva
IAP, Frankfurt am Main
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.
DESY Zeuthen, Zeuthen
A positron source based on a helical undulator system is planned to be used for the future International Linear Collider (ILC). Depending on the accelerator design it will be possible to get polarized positrons at the interaction point. A source performance with high positron yield and high polarization is the aim of our design studies. We focus on the optimization of target and capture section using several simulation codes. FLUKA is a suitable tool to calculate the positron yield, heat deposition, neutron generation and induced activity of source parts. The ASTRA code is used to calculate positron capture efficiency into the optical matching device. The new release of Geant4 includes the spin dependence of all QED processes and allows to perform a helicity-dependent tracking of particles through target and capture section. Starting with a cross-check, the synergy of these three codes allowed to specify the the parameters of a polarized positron source.
Universita di Messina, Messina
INFN - Gruppo Messina, S. Agata, Messina
KEK, 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.
LAL, Orsay
IFIC, Valencia
CERN, Geneva
Uppsala University, Uppsala
CERN, Geneva
Misalignments in the main linac of future linear colliders can lead to significant emittance growth. Beam-based alignment algorithms, such as Dispersion Free Steering (DFS), are necessary to mitigate these effects. We study how to use the Bunch Compressor to create the off-energy beams necessary for DFS and discuss the effectiveness of this method.
CERN, Geneva
Complex beam-based alignment procedures are needed in future linear colliders to reduce the negative effects of static imperfections in the main linac on the beam emittance. The efficiency of these procedures could be affected by dynamic imperfections during their application. In this paper we study the resulting emittance growth.
Royal Holloway, University of London, Surrey
STFC/RAL, Chilton, Didcot, Oxon
SLAC, Menlo Park, California
Birmingham University, Birmingham
Cockcroft Institute, Warrington, Cheshire
STFC/RAL, Chilton, Didcot, Oxon
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Liverpool University, Science Faculty, Liverpool
Durham University, Durham
SLAC, Menlo Park, California
JAI, Oxford
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Experiment T-488 at SLAC, End Station A recorded distorted BPM voltage signals and an accurate simulation of these signals was performed. Geant simulations provided the energy and momentum spectrum of the incident spray and secondary emissions, and a method via image charges was used to convert particle momenta and number density into BPM stripline currents. Good agreement was achieved between simulated and measured signals. Further simulation of experiment T-488 with incident beam on axis and impinging on a thin radiator predicted minimal impact due to secondary emission. By extension to worst case conditions expected at the ILC, simulations showed that background hits on BPM striplines would have a negligible impact on the accuracy of beam position measurements and hence the operation of the FONT feedback system
Liverpool University, Science Faculty, Liverpool
DESY, Hamburg
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
STFC/RAL, Chilton, Didcot, Oxon
Cockcroft Institute, Warrington, Cheshire
OXFORDphysics, Oxford, Oxon
Polarized electron and positron beams are foreseen for the future International Linear Collider (ILC), with polarized electrons already included in the baseline design and polarized positrons seen as a highly-desirable upgrade. High precision physics requires the polarization of both beams to be known with a relative uncertainty of approximately 0.5% or better. Therefore all possible depolarization effects that could operate between the polarized sources and the interaction regions have to be carefully modelled. The "heLiCal" collaboration aims to provide a full "cradle-to-grave" analysis of all depolarization effects at the ILC, and to develop software tools to carry out appropriate computer simulations. In this paper we report on the first phase of our work which includes extensive simulations of the ILC spin-dynamics and a detailed study of beam-beam depolarization effects at the interaction point(s).
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
Illinois Institute of Technology, Chicago, Illinois
For an ILC undulator-based positron source target configuration, a strong optical matching device (OMD) field is needed inside the target to increase the positron yield (by more than 40%)[1]. It is also required that the positron target is constantly rotated to reduce thermal and radiation damage. We report on a simulation of the rotating metal target wheel under a strong magnetic field. By rearranging Maxwell?s equations for a rotating frame and using FEMLAB, we have solved the detailed magnetic field distribution and eddy current of a rotating metal disk in magnetic field, and so the required power to drive the target wheel. In order to validate the simulation process, we have compared our results with previous experimental data [2] and found they are in very good agreement, but differ from previous approximate models [3]. Here we give detailed results on the proposed ILC target system, such as induced magnetic field (dipole and higher orders), eddy current distribution and the driving force requirements. The effect of these higher order fields on the positron beam dynamics is also considered.
ANL, Argonne, Illinois
ANL, Argonne, Illinois
Euclid TechLabs, LLC, Solon, Ohio
Illinois Institute of Technology, Chicago, Illinois
* H. Brechna, D. A. Hill and B. M. Bally, "150 KOe Liquid Nitrogen Cooled Flux Concentrator Magnet", Rev. Sci. Instr., 36 1529,1965.
Jefferson Lab, Newport News, Virginia
Muons, Inc, Batavia
Parametric-resonance ionization cooling (PIC) is a muon-cooling technique that is useful for low-emittance muon colliders. This method requires a well-tuned focusing channel that is free of chromatic and spherical aberrations. In order to be of practical use in a muon collider, it also necessary that the focusing channel be as short as possible to minimize muon loss due to decay. G4Beamline numerical simulations are presented of a compact PIC focusing channel in which spherical aberrations are minimized by using design symmetry.
Fermilab, Batavia, Illinois
Recently we have measured the transverse emittance using both multi-screen as well as muli-slit methods for a range of electron beam intensities from 1 nC to 4 nC at A0 Photoinjector facility at Fermilab. The data have been taken with un-stacked 2.5 ps laser pulse. In this paper we report on these measurements and compare the results with the predictions from beam dynamics calculations using ASTRA and General Particle Tracer including 3D space charge effects.
Fermilab, Batavia, Illinois
SLAC, Menlo Park, California
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
This paper reports the studies of using global emittance tuning bumps to limit the emittance growth to very small values in the main linac of the proposed International Linear Collider (ILC) machine. Simulation studies indicate that closed-orbit emittance bumps, when used after local or quasi-local beam based alignment techniques, can be utilized to further suppress the emittance growth in the ILC main linac. A series of simulations are performed to find the optimal number of bumps and their locations. A more general method of optimizing the emittance bumps in the ILC main linac is also discussed.
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
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.
MIT/PSFC, Cambridge, Massachusetts
High gradient structure design entails optimization of the gradient, while minimizing surface electric fields (associated with breakdown) and surface magnetic fields (associated with pulsed heating). Design studies are reported comparing metallic and dielectric PBG structures and standard disk-loaded waveguide. Operation in a higher order mode is considered. A variety of codes; HFSS, CST MWS, and Superfish have been used to compare and refine designs. Final design work is in preparation for a structure to be cold tested, tuned, and then processed to high gradient operation at the MIT HRC 17 GHz accelerator facility.
MIT/PSFC, Cambridge, Massachusetts
We present the results of our recent research on 3D metal-wire lattices operating at microwave frequencies, with applications to advanced accelerator structures and radiation sources based on the Smith-Purcell effect. Bulk and surface electromagnetic waves supported by a diamond-like lattice are calculated using HFSS. The bulk modes are determined using primitive cell calculations. The surface mode is determined using the simulations of the stack of cells with the perfect-matching layer (PML) boundary.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne, Illinois
Uppsala University, Uppsala
KEK, Ibaraki
CERN, Geneva
Fermilab, Batavia, Illinois
DESY, Hamburg
SLAC, Menlo Park, California
In an effort to compare beam dynamics and create a ‘‘benchmark'' for Dispersion Free Steering (DFS) a comparison was made between different International Linear Collider (ILC) simulation programs while performing DFS. This study consisted of three parts. First, a simple betatron oscillation was tracked through each code. Secondly, a set of component misalignments and corrector settings generated from one program was read into the other to confirm similar emittance dilution. Thirdly, given the same set of component misalignments DFS was performed independently in each program and the resulting emittance dilution was compared. Performance was found to agree exceptionally well in all three studies.
LLNL, Livermore, California
A new cathode design has been proposed for the Flash X-Ray (FXR) induction linear accelerator with the goal of lowering the beam emittance. The present design uses a conventional Pierce geometry and applies a peak field of 134 kV/cm (no beam) to the velvet emission surface. Voltage/current measurements indicate that the velvet begins emitting near this peak field value and images of the cathode show a very non-uniform distribution of plasma light. The new design has a flat cathode/shroud profile that allows for a peak field stress of 230 kV/cm on the velvet. The emission area is reduced by about a factor of four to generate the same total current due to the greater field stress. The relatively fast acceleration of the beam, approximately 2.5 MeV in 10 cm, reduces space charge forces that tend to hollow the beam for a flat, non-Pierce geometry. The higher field stress achieved with the same rise time is expected to lead to an earlier and more uniform plasma formation over the velvet surface. Simulations of the proposed design are presented.
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.
SLAC, Menlo Park, California
LBNL, Berkeley, California
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
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
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.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
In the recent plasma wakefield accelerator experiments at SLAC, the energy of the particles in the tail of the 42 GeV electron beam were doubled in less than one meter [1]. Simulations suggest that the acceleration length was limited by a new phenomenon – beam head erosion in self-ionized plasmas. In vacuum, a particle beam expands transversely in a distance given by beta*. In the blowout regime of a plasma wakefield [2], the majority of the beam is focused by the ion channel, while the beam head slowly spreads since it takes a finite time for the ion channel to form. It is observed that in self-ionized plasmas, the head spreading is exacerbated compared to that in pre-ionized plasmas, causing the ionization front to move backward (erode). A simple theoretical model is used to estimate the upper limit of the erosion rate for a bi-gaussian beam by assuming free expansion of the beam head before the ionization front. Comparison with simulations suggests that half this maximum value can serve as an estimate for the erosion rate. Critical parameters to the erosion rate are discussed.
[1] I. Blumenfeld et al., Nature 445, 741(2007)[2] J. B. Rosenzweig et al., Phys. Rev. A 44, R6189 (1991)
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.
JINR, Dubna, Moscow Region
SLAC, Menlo Park, California
DESY Zeuthen, Zeuthen
SLAC, Menlo Park, California
The main linac of the International Linear Collider (ILC) accelerates short, high peak current bunches into the Beam Deliver System (BDS) on the way to the interaction point. In the BDS wakefields are excited by the resistance of the beam pipe walls and by beam pipe transitions that will tend to degrade the emittance of the beam bunches. In this report we calculate the effect on emittance of incoming jitter or drift, and of misalignments of the beam pipes with respect to the beam axis, both analytically and through multi-particle tracking. Finally, we discuss ways of ameliorating the wake effects in the BDS.
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
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)
KEK, Ibaraki
CERN, Geneva
CLASSE, Ithaca
The very small vertical beam emittance in the International Linear Collider (ILC) can be degraded by dispersion, xy coupling, transverse wakefields, and time-varying transverse fields introduced by elements with misalignments, strength errors, xy rotation errors, or yz rotation errors in the Ring to Main Linac (RTML) transfer line. We present a plan for emittance preservation in this beamline which uses local, quasi-local, and global correction schemes. Results of simulations of the emittance preservation algorithm are also presented and discussed.
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.
NRL, Washington, DC
Euclid TechLabs, LLC, Solon, Ohio
KEK, Ibaraki
ANL, Argonne, Illinois
* C. Jing, W. Gai, J. Power, R. Konecny, S. Gold, W. Liu and A. Kinkead, IEEE, Trans. PS, vol.33 No.4, Aug. 2005, pp.1155-1160.
ANL, Argonne, Illinois
Euclid TechLabs, LLC, Solon, Ohio
Based on our previous experiment that successfully demonstrated wakefield transformer ratio enhancement in a 13.625 GHz dielectric-loaded collinear wakefield accelerator using the ramped bunch train technique, we present here a redesigned experimental scheme for even higher enhancement of the efficiency of this accelerator. Design of a collinear wakefield device with a transformer ratio R>>2, is presented. Using a ramped bunch train (RBT) rather than a single drive bunch, the enhanced transformer ratio (ETR) technique is able to increase the transformer ratio R above the ordinary limit of 2. To match the wavelength of the fundamental mode of the wakefield with the bunch length (σz=2 mm) of the new Argonne Wakefield Accelerator (AWA) drive gun, where the experiment will be performed, a 26.625 GHz dielectric based accelerating structure is required. This transformer ratio enhancement technique based on our dielectric-loaded waveguide design will result in a compact, high efficiency accelerating structure for future wakefield accelerators.
Euclid TechLabs, LLC, Solon, Ohio
KEK, Ibaraki
Due to the high magnetic field-induced surface currents on its conducting sleeve, a conventional single layer Dielectric-Loaded Accelerating (DLA) structure exhibits a relatively high RF loss. One possible way to solve this problem is to use multilayered DLA structures*. In these devices, the RF power attenuation is reduced by making use of the Bragg Fiber concept: the EM fields are well confined by multiple reflections from multiple dielectric layers. This paper presents the design of an X-band dual layer DLA structure as well as the results of bench tests of the device. We will also present results on the design, numerical modeling, and fabrication of structures for coupling RF into multilayer DLAs such as a novel TM03 mode launcher and a TM01-TM03 mode converter using dielectric-loaded corrugated waveguide.
* C. Jing, W. Liu, W. Gai, J. G. Power, and T. Wong, Nucl. Instr. Meth. Phy. Res. A 539 (2005) 445-454.
Euclid TechLabs, LLC, Solon, Ohio
Omega-P, Inc., New Haven, Connecticut
New low loss ferroelectric ceramic materials* possessing large variations in the permittivity as a function of the electric field present interesting and potentially useful applications for dielectric loaded accelerating structures, both wakefield-based and driven by an external rf source. We will consider X-band cylindrical dielectric structures and report numerical results on frequency multiplication, wave steepening and shock formation, and the effect of nonlinearities on the mode structure of these devices. We will examine applications of nonlinear dielectric devices to high gradient acceleration, rf sources, and beam diagnostics.
* ''Fast Switching Ferroelectric Materials for Accelerator Applications'', A. Kanareykin et al., Proceedings of Advanced Accelerator Concepts 2006 (in press)
BNL, Upton, Long Island, New York
University of California IIrvine, Irvine, California
Muons, Inc, Batavia
UCI, Irvine, California
Plasma lens concept is examined as an alternative to focusing horns and solenoids for a neutrino beam facility. The concept is based on a combined high-current lens/target configuration. Current is fed at an electrode located downstream from the beginning of the target where pion capturing is needed. Some of the current flows through the target, while the rest is carried by plasma outside the target. A second plasma lens section, with an additional current feed, follows the target. Plasma of this section is immersed in a solenoidal magnetic field to facilitate its current profile shaping to optimize pion capture. Simulation of the second section alone yielded a 10% higher neutrino production than the horn system. Plasma lenses have additional advantages: larger axial currents, high signal purity: minimal neutrino background in anti-neutrino runs. Lens medium consists of plasma, consequently, particle absorption and scattering is negligible. Withstanding high mechanical and thermal stresses is not an issue. Results of capturing and focusing obtained for various plasma lens configurations will be presented.
Fermilab, Batavia, Illinois
BNL, Upton, Long Island, New York
Muons, Inc, Batavia
UMiss, University, Mississippi
We propose a complete scheme for cooling a muon beam for a muon collider. We first outline the parameters required for a multi-TeV muon collider. The cooling scheme starts with the front end of the Study 2a proposed Neutrino Factory. This yields bunch trains of both muon signs. Emittance exchange cooling in upward climbing helical lattices then reduces the longitudinal emittance until it becomes possible to combine the trains into single bunches, one of each sign. Further cooling is now possible in emittance exchange cooling rings. Final cooling to the required parameters is achieved in 50 T solenoids that use high temperature superconductor. Preliminary simulations of each element will be presented.
IF-UFRGS, Porto Alegre
The goal of this work is to analyze the envelope dynamics of magnetically focused and high-intensity charged particle beams. As known, beams with mismatched envelopes decay into its equilibrium state with a simultaneous increasing of emittance. This emittance growth implies that, in the stationary regime, the transverse phase-space of the beam is characterized by a tenuous population of hot particles around a dense population of cold particles. To describe this emittance growth, it was used the test-particle approach for the development of a simplified self-consistent macroscopic model, whose self-consistency is a result of the inclusion of the emittance growth into the envelope equation. The model is then compared with full N-particle beam simulations and the agreement is shown to be quite reasonable. The model revealed to be useful to understand the physical aspects of the problem and is computationally faster when compared with full simulations.
IF-UFRGS, Porto Alegre
We start by analyzing the image effects of a cylindrical conducting pipe on a continuous beam with elliptical symmetry. In particular, we derive an exact expression for the self-field potential of the beam inside the pipe without using any sort of multipole expansion. By means of a variational method, the potential for beams with varying density profiles along an elliptical shape is used to search for equilibrium solutions for intense beams. For that, we assume a uniform focusing in the smooth-focusing approximation. A curious result is that the product of the rms sizes along the ellipsis semi-axis stays constant as the pipe radius is varied. Finally, we prove that despite the nonlinear forces imposed by the image charges of an arbitrary shape conducting pipe, intense beams in uniform focusing fields preserve a uniform density in the equilibrium.
TRIUMF, Vancouver
TRIUMF, Vancouver
The Enge function can be used to parametrize any element with well-defined edges. If an element is too short, however, there is no unambiguous definition of the effective edge. We first demonstrate that very little fringe field detail is needed to obtain accurate maps even up to fifth order. Then we go on to show a simple fitting algorithm that works well for short as well as long quadrupoles. The results are true whether the quads are magnetic or electrostatic.
CERN, Geneva
CERN, Geneva
EPFL, Lausanne
It's been shown in previous conferences [*,**] that action and phase jump analysis is a promising method to measure normal quadrupole components, skew quadrupole components and even normal sextupole components. In this paper, the action and phase jump analysis is evaluated using new RHIC data.
*J. Cardona,et al, Procceedings of PAC 2005, Knoxville, Tennesse.**J. Cardona,et al, Procceedings of EPAC 2004, Lucerne, Switzerland.
UNAL, Bogota D. C
Simbad code is used to study the combined effect of external non linearities and space charge non linearities on the beam stability using a simple FODO lattice. Gaussian and parabolic particle distribution are used for these simulations and results are compared with Mohl and Metral theoretical results.
GSI, Darmstadt
IUCF, Bloomington, Indiana
GSI, Darmstadt
GSI, Darmstadt
Transverse stability due to combinations of chromaticity effect, nonlinear space charge and octupoles of different polarities plays an important role in the determination of the impedance budget for the FAIR synchrotrons. Different analytic approaches [*,**,etc.] have been suggested, for which no direct comparison has been made so far. In order to clarify this issue we perform numerical investigations employing the particle tracking code PATRIC and compare results of simulation scans with predictions of a dispersion relation. Space charge effects within self-consistent and 'frozen' models are used for comparisons, connection to beam transfer function studies is addressed.
* D. Moehl, CERN/PS 95-08 (DI), (1995)** M. Blaskiewicz, Phys. Rev. ST Accel. Beams 4, 044202, (2001)
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.
TEMF, Darmstadt
Accurate computations of wake potentials are an important task in modern accelerator design. Short bunches used in high energy particle accelerators excite very high-frequency fields. The geometrical size of accelerating structures exceeds the wavelength of the excited fields by many orders of magnitude. The application of codes such as TBCI, MAFIA or tamBCI are limited due to numerical dispersion effects and memory needs. Recently new codes like PBCI have been developed to overcome these problems. In this work the utilization of dispersionless directions in the leap-frog update scheme on a Cartesian grid are proposed for accurate simulations. In conjunction with a conformal modelling technique which allows for the full Courant time step a moving window technique can be applied. This was previously implemented in a 2D code. In this publication an extension to arbitrary three dimensional problems are presented.
TEMF, Darmstadt
For the coupled simulation of charged particles and electromagnetic fields several techniques are known. In order to achieve accurate results various parameters have to be taken into account. The number of macro-particles per cell, the resolution of the computational grid, and other parameters strongly affect the accuracy of the results. In the code tamBCI, based on a time-adaptive mesh, additional variables related to the adaptive grid refinement have to be chosen appropriately. An analysis of these values is carried out and the results are applied to the self-consistent simulation of the injector section of FLASH in 3D.
DESY, Hamburg
The International Linear Collider (ILC) requires the preservation of an ultra-small vertical emittance from the Damping Ring to the Interaction Point (IP) where the nanometre-sized beams are made to collide. It is well-known that ground motion and component vibration will need to be compensated by fast intra-train feedback systems and slower semi-continuous trajectory corrections. This complex system can in general only be modelled using simulation. In this paper, we report the progress and status of a full-featured so-called start-to-end simulation based on the MERLIN package of the ILC Low Emittance Transport (LET): Bunch compression, acceleration in the superconducting Main Linac, Beam Delivery System and finally collision at the IP. Realistic modelling of the beam-beam is included by using the code GUINEAPIG. Results based on several ground motion and vibration models and configurations of trajectory control are presented.
DESY, Hamburg
Uni HH, Hamburg
GSI, Darmstadt
Bologna University, Bologna
We present the upgrade of the MICROMAP beam dynamics simulation library to include a 2 1/2 D space charge modeling of a 3D bunch using local slices in z. We discuss the parallelization technique, the performances, several tests and comparison with existing well-established analytical/numerical results in order to validate the code. An application to the SIS100 synchrotron of the FAIR project at GSI is outlined.
BNL, Upton, Long Island, New York
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Tokyo
* T. Abe and H. Yamamoto, Phys. Rev. ST Accel. Beams 7, 072802 (2004)
KEK, Ibaraki
KEK, Ibaraki
JAEA/LINAC, Ibaraki-ken
JAEA, Ibaraki-ken
KEK, Ibaraki
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
Hokkaido University, Sapporo
TEMF, Darmstadt
Muroran Institute of Technology, Department of Electrical and Electronic Engineering, Muroran
CNS, Saitama
Utsunomiya University, Utsunomiya
* S. Van der Meer, CERN/PS/AA/78-22, 1978.** T. Yabe and T. Aoki, Comp. Phys. Commun. 66 (1991) 219.
TIT, Yokohama
Utsunomiya University, Utsunomiya
For researches in high energy density physics and inertial confinement fusion by using heavy ion beams, high-current beam dynamics should be understood well. The heavy ion beam is longitudinally compressed by a head-to-tail velocity tilt applied from high-power induction voltage modules. In this study, emittance growth due to the longitudinal bunch compression is numerically investigated by using a particle-in-cell simulation. The code developed is dealt with three dimensional particle motions, and 2D transverse electric field is solved by Poisson equation coupled with 1D longitudinal electric field. We indicate the particle dynamics due to the non-linear longitudinal-transverse coupling effect around the stagnation point in the longitudinal compression.
TUB, Beijing
LBNL, Berkeley, California
BINP SB RAS, Novosibirsk
IC SB RAS, Novosibrsk
ICM&MG SB RAS, Novosibirsk
CERN, Geneva
BNL, Upton, Long Island, New York
UMAN, Manchester
Royal Holloway, University of London, Surrey
CERN, Geneva
Lancaster University, Lancaster
DESY, Hamburg
CERN, Geneva
CERN, Geneva
BNL, Upton, Long Island, New York
GSI, Darmstadt
KEK, Ibaraki
SLAC, Menlo Park, California
LBNL, Berkeley, California
LBNL, Berkeley, California
PSI, Villigen
Liverpool University, Science Faculty, Liverpool
UMAN, Manchester
Cockcroft Institute, Warrington, Cheshire
LANL, Los Alamos, New Mexico
Voss Scientific, Albuquerque, New Mexico
SAIC, Los Alamos, New Mexico
The ion-hose instability sets limits on the allowable vacuum in the DARHT-2 linear induction accelerator (2kA, 18.6MeV, 2μs). Lamda is a transport code which advances the beam centroid and envelope in a linear induction accelerator from the injector to the final focus region. The code computes the effect of magnet misalignments, beam breakup instability, image-displacement instability, and gap voltage fluctuation on the beam. In this work, we have implemented the Spread Mass (SM) model of ion-hose instability into Lamda so that we can examine quickly the operating parameters for the experiments. Unlike the ordinary SM ion-hose code which assumes the uniform axial magnetic field, Lamda ion-hose calculation includes varying axial magnetic field, accelerating beam, gas pressure file, varying beam radius and elliptical beam. The benchmarks against a semi-analytical SM code and the particle-in-cell code Lsp, and a prediction of ion-hose instability for a 2.5MeV-1.4kA beam in the DARHT-2 are presented.
Voss Scientific, Albuquerque, New Mexico
UNM, Albuquerque, New Mexico
SLAC, Menlo Park, California
We report on the implementation of a self consistent particle code to study CSR effects on particle bunches traveling on arbitrary planar orbits. Shielding effects are modeled with parallel perfectly conducting plates. The "vertical" charge distribution is assumed to be stationary. The macroscopic Maxwell equations are solved in the lab frame while the equations of motion are integrated in the beam frame interaction picture where the dynamics is governed by the self fields alone. We study different methods to construct a smooth charge density from particles, e.g. gridless nonparametric curve estimation and charge deposition plus filtering. We present numerical results for bunch compressors. In particular, we study different initial distributions. The transverse initial distribution is Gaussian and we study different initial longitudinal distributions: Gaussian, parabolic and nonlinear chirp. A parallel version of the code has been implemented and this will speed up parameter analysis and allow micro-bunching studies.
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
The linear growth of the two-stream instability for a charged particle beam that is longitudinally compressing as it propagates through a background plasma (due to an applied velocity tilt) is examined. Detailed, 1D particle-in-cell simulations are carried out to examine the growth of a wave packet produced by a small amplitude density perturbation in the background plasma. Recent analytic and numerical work by Startsev and Davidson [1] predicted reduced linear growth rates, which are indeed observed in the simulations. Here, small-signal asymptotic gain factors are determined in a semi-analytic analysis and compared with the simulation results in the appropriate limits. Nonlinear effects in the PIC simulations, including wave breaking and particle-trapping, are found to limit the linear growth phase of the instability for both compressing and non-compressing beams.
[1] Phys. Plasmas 13, 62108 (2006)
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
Longitudinal bunching factors in excess of 70 of a 300-keV, 27-mA K+ ion beam have been demonstrated in the Neutralized Drift Compression Experiment in rough agreement with LSP particle-in-cell end-to-end simulations. These simulations include both the experimental diode voltage and induction bunching module voltage waveforms in order to specify the initial beam longitudinal phase space critical to longitudinal compression. To maximize simultaneous longitudinal and transverse compression, we designed a solenoidal focusing system that compensated for the impact of the applied velocity tilt on the transverse phase space of the beam. Here, pre-formed plasma provides beam neutralization in the last one meter drift region where the beam perveance becomes large. Integrated LSP simulations, that include detailed modeling of the diode, magnetic transport, induction bunching module, plasma neutralized transport, were critical to understanding the interplay between the various accelerator components. Here, we compare simulation results with the experiment and discuss the contributions to longitudinal and transverse emittance that limit compression.
ANL, Argonne, Illinois
KEK, Ibaraki
ANL, Argonne, Illinois
ANL, Argonne, Illinois
In recent years, we have explored various upgrade options for the Advanced Photon Source (APS) storage ring that would provide the user community higher brightness. Increased brightness would be accomplished by reducing the emittance of the storage ring as well as increasing the stored beam current from 100 mA to 200 mA. Two upgrade lattices were developed that reduce the effective beam emittance to 1 nm from the present 2.7 nm. These lattices have reduced dynamic aperture compared to the present ring lattice, which may require a reduced emittance booster to minimize injection losses. This paper describes injection tracking simulations that explore how high the booster emittance can be and still have no losses at injection for the 1-nm ring upgrade lattices. An alternative booster lattice is presented with reduced emittance compared to the present booster lattice (65 nm). The proposed low-emittance booster lattice would add pole-face windings to the existing booster dipoles and hence would not require replacement of the existing booster magnets.
ANL, Argonne, Illinois
Northern Illinois University, DeKalb, Illinois
Transverse-to-longitudinal emittance exchange can be achieved through certain arrangements of dipole magnets and dipole mode rf cavity. Theory on such schemes has been developed in the past several years. In this paper we report our numerical simulations on the emittance exchange using particle tracking codes. Photoelectron beams with energy less than 20 MeV are used, as our purpose of simulations is to study the feasibility of performing such emittance exchange at existing facilities of beam energy at this level. Parametric studies of the dipole magnets and cavity strengths, as well as initial beam parameters, are presented.
ANL, Argonne, Illinois
The program Elegant* is widely used for design and modeling of linacs for free-electron lasers and energy recovery linacs, as well as storage rings and other applications. As part of a multi-year effort, we have parallelized many aspects of the code, including single-particle dynamics, wakefields, and coherent synchrotron radiation. We report on the approach used for gradual parallelization, which proved very beneficial in getting parallel features into the hands of users quickly. We also report details of parallelization of collective effects. Finally, we discuss performance of the parallelized code in various applications.
*M. Borland, APS Light Source Note LS-287, September 2000.
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.
ANL, Argonne, Illinois
Large scale beam dynamics simulations are important to support the design and operations of an accelerator. From the beginning, the beam dynamics code TRACK was developed to make it useful in the three stages of a hadron (proton and heavy-ion) linac project, namely the design, commissioning and operation of the machine. In order to combine the unique features of TRACK with large scale and fast parallel computing we have recently developed a parallel version of the code*. We have successfully benchmarked the parallel TRACK on different platforms: BG/L and Jazz at ANL, Iceberg at ARSC, Lemieux at PSC and Seaborg at NERSC. We have performed large scale RFQ and end-to-end simulations of the FNAL proton driver where particles were simulated. The actual parallel version has the potential of simulating particles on 10 racks with 20,480 processors of BG/L at ANL, which will be available soon. After a brief description of the parallel TRACK, we'll present results from highlight applications.
* "Parallelization of a Beam Dynamics Code and First large Scale RFQ Simulations", J. Xu, B. Mustapha, V. N. Aseev and P. N. Ostroumov, accepted for publication in PRST-AB.
Illinois Institute of Technology, Chicago, Illinois
G4beamline is a single-particle simulation program optimized for the design and evaluation of beam lines. It is based on the Geant4 toolkit, and can implement accurate and realistic simulations of particle transport in both EM fields and in matter. This makes it particularly well suited for studies of muon collider and neutrino factory design concepts. G4beamline includes a rich repertoire of beamline elements and is intended to be used directly without C++ programming by accelerator physicists. The program has been enhanced to handle a larger class of beamline and detector systems, and to run on Linux, Windows, and Macintosh platforms.
Fermilab, Batavia, Illinois
CHEF is both a framework and an interactive application emphasizing accelerator optics calculations. The framework supports, using a common infrastructure, multiple domains of applications: e.g. nonlinear analysis, perturbation theory, and tracking. Its underlying philosophy is to provide infrastructure with minimum hidden implicit assumptions, general enough to facilitate both routine and specialized computational tasks and to minimize duplication of necessary, complex bookkeeping tasks. CHEF was already described in recent conferences. In this paper we present a status report on the most recent developments, including issues related to its application to high energy linacs.
Fermilab, Batavia, Illinois
Mxyzptlk was one of the early and, to this day, limited number of differentiation engines implemented by taking full advantage of a language with operator overloading capabilities. It was created with an eye at enabling accelerator related computations, especially within the realm of perturbation theories. Such computations are supported by (1) a one-to-one correspondence between original mathematical abstractions and the data types and operations used to implement them; (2) the exact computation of high order derivatives. Significant efforts were invested recently in modernizing Mxyzptlk both architecturally and algorithmically. Among other things, these substantially improved performance and usabilty. We present a description of the current Mxyzptlk from both standpoints and describe its current capabilities and performance.
Fermilab, Batavia, Illinois
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).
LLNL, Livermore, California
LBNL, Berkeley, California
PPPL, Princeton, New Jersey
UCB, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
This work was supported by the Office of Fusion Energy Sciences, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231, W-7405-Eng-48, DE-AC02-76CH3073 for HIFS-VNL.
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
LANL, Los Alamos, New Mexico
Lehigh University, Bethlehem, Pennsylvania
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.
Tech-X, Boulder, Colorado
LBNL, Berkeley, California
The standard implementation of using FFTs to solve the Poisson equation with open boundary conditions on a Cartesian grid loses accuracy when the change in G rho (the product of the Green function and the charge density) over a mesh cell becomes nonlinear; this is commonly encountered in high aspect ratio situations and results in poor efficiency due to the need for a very large number of grid points. A modification which solves this problem, the integrated Green function (IGF), has been implemented in two dimensions using linear basis functions and in three dimensions using constant basis functions. But, until recently, it has proved to be very difficult to implement IGF in three dimensions using linear basis functions. Recently significant progress has been made. We present both the implementation and test results for the three-dimensional extension.
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.
Tech-X, Boulder, Colorado
Fermilab, Batavia, Illinois
ANL, Argonne, Illinois- addressing multilanguage interoperability in the MaryLie/Impact code with Babel;
- creating components by making the selected software objects adhere to the Common Component Architecture protocol;
- assemblying the components with a newly developed, Component Builder gui; and
- characterizing the performance of the space charge (Poisson) solver that was originally used in Synergia 1.0 versus the PETSc-based space charge solver that has been developed for Synergia2.
A component-based beam dynamics application for modeling collective effects in particle accelerators has been developed. The Common Component Architecture (CCA) software infrastructure was used to compose a new Python-steered accelerator simulation from a set of services provided by two separate beam dynamics packages (Synergia and MaryLie/Impact) and two high-performance computer science packages (PETSc and FFTW). The development of the proof-of-concept application was accomplished via the following tasks:
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.
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.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne, Illinois
An Exotic Beam Facility is one of the highest priority projects in the DOE 20-year plan and a major strategic initiative for Argonne. The main components of the facility are a high-power multi-beam superconducting heavy-ion accelerator, a production complex, and finally a high-efficiency post-accelerator. This talk revolves around new approaches to heavy-ion beam dynamics for the central part, the Fragment Separators. To this end, it will summmarize the theories developed, software written, and simulations done that lead to better understanding of basic beam dynamics, more insight towards the best design choices, and optimization of the system?s parameters, including the integrated beam optics-nuclear physics approach.
G. H. Gillespie Associates, Inc., Del Mar, California
The Particle Beam Optics Laboratory, or PBO Lab, is a suite of software applications developed to support beamline design, accelerator operations, and personnel training. The software provides an intuitive and easy-to-use graphic user interface (GUI) that works with a variety of particle optics codes. The PBO Lab GUI is largely responsible for the popularity of this software suite, which is now used at more than ninety institutions throughout the world. While PBO Lab greatly improves the human-machine interface for several popular optics programs, it has historically required a significant effort to incorporate additional optics codes into the software suite. The Open Architecture Software Integration System, or OASIS, provides an innovative framework that allows users to readily integrate their own optics programs into PBO Lab. This paper provides an overview of the OASIS framework and describes some of the new PBO Lab Modules that have been created using OASIS.
NSCL, East Lansing, Michigan
RIKEN, Saitama
Gas stopping is the method of choice to convert high-energy beams of rare isotopes produced by projectile fragmentation into low-energy beams. Fast ions are slowed down in solid degraders and stopped in a buffer gas in a stopping cell, presently linear. They have been successfully used for first precision experiments with rare isotopes*,** but they have beam-rate limitations due to space charge effects. Their extraction time is about 100 ms inducing decay losses for short-lived isotopes. At the NSCL a new gas stopper concept*** is under development, which avoids these limitations and fulfills the needs of next-generation rare isotope beam facilities. It uses a gas-filled cyclotron magnet. The large volume, and a separation of the regions where the ions stop and where the maximum ionization is observed are the key to a higher beam-rate capability. The longer stopping path due to the magnetic field allows a lower pressure to be used, which decreases the extraction times. The concepts of the cyclotron gas stopper will be discussed and the results from detailed simulation and design work towards the realization of such a device at the NSCL will be summarized.
* G. Bollen et al., Phys. Rev. Lett. 96 (2006) 152501 ** R. Ringle Phys. Rev. C Submitted*** G. Bollen et al., Nucl. Instr. Meth. A550 (2005) 27
CLASSE, Ithaca
One of the main concerns in the design of a high energy Energy Recovery Linac x-ray source is the preservation of beam emittance. Discussed is one possible source of emittance dilution due to transverse electromagnetic fields in the accelerating cavities of the linac caused by the power coupler geometry. This has already been found to be a significant effect in Cornell's ERL injector cavities if only one coupler per cavity is chosen. Here we present results of simulations for Cornell's main ERL linac with three possible coupler configurations and compare them with regards to total normalized emittance growth after one complete pass through the linac. We explain why the sign of the phase between the transverse kick and the accelerating force alternates each cavity, which leads to a cancellation of the emittance growth to acceptable values. We also investigate the effect of cavity detuning on the coupler-kick effect.
CLASSE, Ithaca
A self-consistant simulation method is developed for the study of coherent synchrotron radiation effects by using a perturbation expansion of retarded radiation field and the particle-in-cell method. The perturbation expansion of the radiation field is based on the fact that the time dependance of a bunch particle distribution has typically two significantly different time scales, a fast time scale related to the linear dynamics and a slow time scale of the beam-size growth due to nonlinear perturbations. Since the scale of the retardation of the radiation field is usually much shorter than the slow time scale of the particle distribution, the retardation on the slow time scale of the particle distribution is treated perturbatively while the retardation on the fast time scale is removed by transformations associated the linear lattice. With this method, the particle-radiation interaction can be calculated in configuration space without memorizing the history of the particle distribution.
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.
ANL, Argonne, Illinois
LANL, Los Alamos, New Mexico
TechSource, Santa Fe, New Mexico
NSCL, East Lansing, Michigan
LBNL, Berkeley, California
RIAPMTQ/IMPACT is a pair of linked beam-dynamics simulation codes that have been developed for end-to-end computer simulations of multiple-charge state heavy-ion linacs for future exotic-beam facilities. The simulations can extend from the low-energy beam transport after the ECR source to the end of the linac. The work has been performed by a collaboration including LANL, LBNL, ANL, MSU, and TechSource. The code RIAPMTQ simulates the linac front end including the LEBT, RFQ, and MEBT, and the code IMPACT simulates the main superconducting linac. The codes have been benchmarked for rms beam properties against previously existing codes at ANL and MSU. The codes allow high-statistics runs on parallel supercomputing platforms, such as NERSC at LBNL, as well as runs on desktop PC computers for low-statistics design work. We will show results from 10-million-particle simulations of RIA designs by ANL and MSU, carried out at the NERSC facility. These simulation codes will allow evaluations of candidate designs with respect to beam-dynamics performance including beam losses.
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
Rome University La Sapienza, Roma
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).
BNL, Upton, Long Island, New York
Fermilab, Batavia, Illinois
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.
The PEP II lattices are unique in their detector solenoid field compensation scheme by utilizing a set of skew quadrupoles in the IR region and the adjacent arcs left and right from the IP. Additionally the design orbit through this region is nonzero. This combined with the strong local coupling wave makes it very difficult to calculate IP tuning knobs which are orthogonal and closed. The usual approach results either in non-closure, not being orthogonal or the change in magnet strength being too big. To find a solution the set of tuning quads had to be extended which resulted having more degrees of freedom than constrains. To find the optimal set of quadrupoles which creates a linear, orthogonal and closed knob and simultaneously minimizing the changes in magnet strength, the method using Singular Value Decomposition, Response Matrices and an Adapted Moore Penrose Method had to be extended. The results of these simulations are discussed below and the results of first implementation in the machine are shown.
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.
The SNS ring injection dump beam line has been suffering high beam losses since its commissioning. In order to understand the mechanisms of the beam losses, we have built a 3D simulation model consisting of three injection chicane dipoles and one injection dump septum. The magnetic field distributions and the 3D particle trajectories in the model are obtained. The study has clearly shown two design problems causing beam losses in the injection dump beam line. This paper reports our simulation model, particle trajectory calculations, beam losses due to small vertical aperture of the injection dump septum and inadequate focusing down stream. The remedy of the beam losses is also discussed.
PPPL, Princeton, New Jersey
The transverse compression and dynamics of intense charged particle beams, propagating through a periodic quadrupole lattice, play an important role in many accelerator physics applications. Typically, the compression can be achieved by means of increasing the focusing strength of the lattice along the beam propagation direction. However, beam propagation through the lattice transition region inevitably leads to a certain level of beam mismatch and halo formation. In this paper we present a detailed analysis of these phenomena using particle-in-cell (PIC) numerical simulations performed with the WARP code. A new definition of beam halo is proposed in this work that provides the opportunity to carry out a quantitative analysis of halo production by a beam mismatch.
PPPL, Princeton, New Jersey
Background plasma can be used as a convenient tool for manipulating intense charge particle beams, for example, for ballistic focusing and steering, because the plasma can effectively reduce the space-charge potential and self-magnetic field of the beam pulse. We previously developed a reduced analytical model of beam charge and current neutralization for an ion beam pulse propagating in a cold background plasma. The reduced-fluid description provides an important benchmark for numerical codes and yields useful scaling relations for different beam and plasma parameters. This model has been extended to include the additional effects of a solenoidal magnetic field and gas ionization. Analytical studies show that a sufficiently large solenoidal magnetic field can increase the degree of current neutralization of the ion beam pulse. The linear system of equations has been solved analytically in Fourier space. For a strong enough applied magnetic field, poles emerge in Fourier space. These poles are an indication that whistler waves and lower hybrid waves are excited by the beam pulse.
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).
PPPL, Princeton, New Jersey
In 3D high-intensity bunched beams, the collective effects associated with strong coupling between the longitudinal and transverse dynamics are of fundamental importance. A direct consequence of this coupling is that the particle dynamics does not conserve transverse energy and longitudinal energy separately, and there exists no exact kinetic equilibrium which has an anisotropic energy in the transverse and longitudinal directions. The strong coupling also introduces a mechanism for the electrostatic Harris-type instability driven by strong temperature anisotropy, which exists naturally in beams that have been accelerated to large velocities. The self-consistent Vlasov-Maxwell equations are applied to high-intensity bunched beams, and a generalized low-noise delta-f particle simulation algorithm is developed for bunched beams with or without energy anisotropy. Systematic studies are carried out that determine the particle dynamics, the approximate equilibrium, and stability properties under conditions corresponding to strong 3D nonlinear space-charge force. Finite bunch-length effects on collective excitations and anisotropy-driven instabilities are also investigated.
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.
UCLA, Los Angeles, California
Many simulation efforts make use of integrated numerical experiments, where the inputs and outputs of several accelerator codes are tied together. This is usually accomplished by writing custom scripts that launch the underlying programs and perform data format translation. We present a way to simplify this process by using a graphical user interface that allows one to describe the data flow in the style of the LabVIEW and Simulink environments. A module to support a new accelerator code involves writing data translators to/from a common format (SDDS or HDF5), and a function to generate an input file based on a standard way of specifying an accelerator lattice (such as Accelerator Markup Language, or AML).
A multipurpose coherent instability simulation code has been written, documented, and released for use. TRANFT (tran-eff-tee) uses fast Fourier transforms to model transverse wakefields, transverse detuning wakes and longitudinal wakefields in a computationally efficient way. Dual harmonic RF allows for the study of enhanced synchrotron frequency spread. When coupled with chromaticity, the theoretically challenging but highly practical post head-tail regime is open to study. Detuning wakes allow for transverse space charge forces in low energy hadron beams, and a switch allowing for radiation damping makes the code useful for electrons.
CERN, Geneva
The tight mechanical aperture for the LHC imposes severe constraints on both the beta and dispersion beating. Robust techniques to compensate these errors are critical for operation of high intensity beams in the LHC. We present simulations using realistic errors from magnet measurements and alignment tolerances in the presence of BPM noise. Correction reveals that the use of BPM calibration and model independent observables are key ingredients to accomplish optics correction. Experiments at RHIC to verify the algorithms for optics correction are also presented.
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.
Fermilab, Batavia, Illinois
ANL, Argonne, Illinois
Rutgers University, The State University of New Jersey, Piscataway, New Jersey
The A0 photoinjector is being reconfigured to test the principal of transverse to longitudinal emittance exchange as proposed by Emma et. al., Kim and Sessler, and others. The ability to perform such an exchange could have major advantages to FELs by reducing the transverse emittance. Several schemes to carry out the exchange are possible and will be reported separately. At the Fermilab A0 Photoinjector we are constructing a beamline to demonstrate this transverse to longitudinal emittance exchange. This beamline will consist of a dogleg, and a TM110 5 cell copper cavity followed by another dogleg. The beamline is designed to reuse the bunch compressor dipoles of the photoinjector, along with some existing diagnostics. Beamline layout and optics discussed along with inital data. Future possibilites of performing a similar experiment at the proposed NML facility at Fermilab are also discussed.
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
The AGS synchrotron employs two partial helical snakes* to preserve the polarization of the proton beam during acceleration in the AGS. The effect of the helical snakes on the beam optics is significant at injection energy, with the effect greatly diminishing early in the acceleration cycle. In order to compensate for the effect of the snakes on the beam optics, we have introduced eight compensation quadrupoles in straight sections of the AGS at the proximity of the partial snakes. At injection the strength of these eight quads is set at a high value but ramped down to zero when the effect of the snakes diminishes. Four of the compensation quadrupoles had to be placed in very short straight sections therefore had to be 'thin' with a length of ~30 cm. The 'thin' quadrupoles were laminated and designed to minimize the strength of the dodecoupole harmonic. The thickness of the lamination was also calculated** to keep the ohmic losses generated by the eddy currents in the laminations below an acceptable limit. Comparison of the measured and calculated harmonics will be presented and the ohmic losses due to the eddy currents, as a function of time during rumping will be discussed.
* H. Huang, et al., Proc. EPAC06, (2006), p. 273.** OPERA computer code. Vector Fields Inc.
BNL, Upton, Long Island, New York
LBNL, Berkeley, California
LLNL, Livermore, California
To provide a compact high-brightness heavy-ion beam source for Heavy Ion Fusion, we have performed experiments to study a proposed merging beamlet approach for the injector. We used an RF plasma source to produce the initial beamlets. An extraction current density of 100 mA/cm2 was achieved, and the thermal temperature of the ions was below 1 eV. An array of converging beamlets was used to produce a beam with the envelope radius, convergence, and ellipticity matched to an electrostatic quadrupole channel. Experimental results were in good quantitative agreement with simulation and have demonstrated the feasibility of this concept. The size of a driver-scale injector system using this approach will be several times smaller than one designed using traditional single large-aperture beams. The success of this experiment has possible significant economical and technical impacts on the architecture of HIF drivers.
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.
GSI, Darmstadt
An examination of heavy ion beam profiles using viewing targets and CCD cameras at both the GSI and NSCL shows highly structured patterns. These structures generally have a 3-fold symmetry reflecting the highly-magnetized nature of the ion formation within the plasma chamber. A program of experiment and three-dimensional modeling with KOBRA3d is continuing. Results of this program to date are discussed.
CERN, Geneva
Fermilab, Batavia, Illinois
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.
ASP, Clayton, Victoria
IF-UFRGS, Porto Alegre
This paper analyzes the combined envelope-centroid dynamics of magnetically focused high-intensity charged beams surrounded by conducting walls. Similarly to the case were conducting walls are absent, we show that the envelope and centroid dynamics decouples from each other. Mismatched envelopes still decay into equilibrium with simultaneous emittance growth, but the centroid keeps oscillating with no appreciable energy loss. Some estimates are performed to analytically obtain some characteristics of halo formation seen in the full simulations.
IF-UFRGS, Porto Alegre
We analyze the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. The theory presented in this paper allows to analytically calculate the time at which the wave breaking takes place. It also gives a good estimate of the time necessary for the beam to relax into the final stationary state consisting of a cold core surrounded by a halo of highly energetic particles.
LAL, Orsay
DESY Zeuthen, Zeuthen
CERN, Geneva
IMCCE, Paris
CERN, Geneva
One of the main limitations for precise tune measurements using kicked turn-by-turn data is the beam decoherence, which can limit the available signal to a reduced number of turns. Applying Laskar's frequency analysis, on measurements from several beam position monitors, a fast and accurate determination of the real tune is possible. The efficiency of the method is demonstrated when applied in turn-by-turn data from the ESRF storage ring and CERN's Super Proton Synchrotron. Estimates from tracking simulations and analytical considerations are further compared with the experimental results.
GSI, Darmstadt
3D simulation studies of the transverse impedance budget for long bunches in the FAIR synchrotrons have been started. Important transverse instability driving sources are the thin resistive wall and the kicker impedances. Major concerns are the required low momentum spreads and the additional loss of Landau damping due to the space charge tune shift. The simulation code PATRIC has been extended in order to predict coherent instability thresholds with space charge and for broadband impedance sources. Examples of code benchmarking using the numerical Schottky noise, analytical stability boundaries and comparisons with other codes will be discussed. The improvement of transverse stability in long bunches relative to a coasting beam is analyzed for different rf wave forms. Conclusions for the impedance budget in the FAIR synchrotrons are drawn.
TEMF, Darmstadt
DESY, Hamburg
One method to measure the bunch shape at the FLASH facility at DESY, Hamburg is based on the observation of synchrotron radiation generated at the first bunch compressor. For the correct interpretation of the results it is mandatory to know how various parameters of the real setup, in contrast to theoretical assumptions, influence the observed spectrum. The aim of this work therefore is to calculate the generation of synchrotron radiation of a moving point charge inside the bunch compressor with the emphasis of including the effects of the vertical and horizontal vacuum chamber walls in the vicinity of the last dipole magnet. Because of the small wavelength in comparison with the chamber geometries this is a demanding task. One idea to cope with the difficulties is to use optical methods such as the uniform theory of diffraction (UTD). In this paper the applicability and limitations of the proposed method are discussed. Furthermore a comparison of simulated and new measured fields is shown.
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.
KEK, Ibaraki
CERN, Geneva
POSTECH, Pohang, Kyungbuk
KEK, Ibaraki
KEK, Ibaraki
KEK, Ibaraki
* Y. Suetsugu et al., NIM-PR-A, Vol.556 (2006) 399.
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
CAEP, Mainyang, Sichuan
KEK, Ibaraki
Kyungpook National University, Daegu
ORNL, Oak Ridge, Tennessee
We are developing a sophisticated system of beam loss pattern evaluation and residual radiation estimation. We have installed a number of Neutron Detectors and Ionization Chambers along LINAC. In this paper we present our implementation and simulation of the losses by inserting Faraday Cups, using Beam Stops and running Wire Scanners at different energies. The measured losses are simulated by 3-D transport codes (GEANT4, SHIELD, MCNPX). We compare two different sets of Beam Loss Monitors: Ionization Chambers (detecting X-ray and gamma radiation) and Photo-Multiplier Tubes with a neutron converter (detecting neutrons) and outline that such a combination is a better way to measure beam losses than relying on detectors of one type. We interpret the loss signal in terms of beam current lost in the SNS LINAC with accurate longitudinal loss distribution and plan to automate beam steering according to loss monitors readings by using vast Loss Pattern Database developed by simulating different loss scenarios with the transport codes.
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
EPFL, Lausanne
CEA, Grenoble
CERN, Geneva
LBNL, Berkeley, California
CERN, Geneva
CERN, Geneva
CERN, Geneva
CERN, Geneva
EPFL, Lausanne
CERN, Geneva
BNL, Upton, Long Island, New York
IFIC, Valencia
In recent years several measurements of the SPS non-linear chromaticity have been performed in order to determine the non-linear optics model of the SPS machine at injection energy for different cycles. In 2006 additional measurements have been performed at injection and during the ramp for the cycle used to accelerate the LHC beam. New and more robust matching algorithms have been developed in 2006 to fit the model to the measurements up to arbitrary chromatic order. In this paper we describe the algorithms used in the analysis of the data and we summarize and compare the results from all experiments.
UMAN, Manchester
UMAN, Manchester
* Cox, Brian et al., "FP420 : An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging Detectors in the 420 m Region of the LHC", CERN-LHCC-2005-025
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
We recently studied a lattice achieving 1-nm emittance at the APS storage ring*. The successful design required very strong sextupoles in order to tune the machine to the desired positive chromaticity. A preliminary design of such magnets indicated saturation in the poles unless the vacuum chamber gets smaller by a factor of two compared to the existing APS chamber. Since the resistive wall impedance scales as 1/b3, where b is the radius of the chamber, we questioned how much current we can store in a single bunch at the 1-nm storage ring. In order to answer this question quantitatively, we calculated all wake potentials of impedance elements of the existing APS storage ring with the transverse dimension properly scaled but with the longitudinal dimension kept unchanged. With the newly calculated impedance of a smaller chamber, we estimated the single-bunch current limit. It turned out that the ring with a smaller chamber would not diminish the single-bunch current limit substantially. We present both wake potentials of 1-nm and the existing rings followed by the simulation results carried out for determining the accumulation limit to the ring.
* A. Xiao, "A 1-nm Lattice for the APS Storage Ring" these proceedings.
ANL, Argonne, Illinois
The first Impedance Database* constructed at the Advanced Photon Source was successfully used in reproducing the main characteristics of single-bunch instabilities observed in the storage ring. However, the finite bandwidth of the corresponding impedance model was limited to 25 GHz, which happens to be the resolution limit of the density modulation observed in the microwave instability simulation. In order to resolve simulation results never verified in the experiments, we decided to extend the calculated bandwidth of impedance to 50 GHz by recalculating the wake potentials excited by a shorter bunch. Since low-order electromagnetic code requires 20-40 grid points per wavelength, reducing the bunch length required a large number of grids for the 3D structure. We used bunch lengths of 1- and 2-mm in the Gaussian distribution in the Impedance Database II project. For the large-scale computation we used the 3D electromagnetic code GdfidL ** for wake potential calculation at the cluster equipped with 240 GB of memory. The resultant wake potential excited by the short bunch together with application to the storage ring for collective effects is presented in the paper.
* Y.-C. Chae, "The Impedance Database and Its Application to the APS Storage Ring" Proc. 2003 PAC, p. 3017.** http://www.gdfidl.de
SLAC, Menlo Park, California
ANL, Argonne, Illinois
In recent years we have explored the application to the Advanced Photon Source (APS) of Zholents' crab-cavity-based scheme for production of short x-ray pulses. As a near-term project, the APS has elected to pursue a pulsed system using room-temperature cavities*. The cavity design has been optimized to heavily damp parasitic modes while maintaining large shunt impedance for the deflecting dipole mode**. We evaluated a system consisting of three crab cavities as an impedance source and determined their effect on the single- and multi-bunch instabilities. In the single-bunch instability we used the APS impedance model as the reference system in order to predict the overall performance of the ring when the crab cavities are installed in the future. For multi-bunch instabilities we used a realistic fill pattern, including hybrid-fill, and tracked multiple bunches where each bunch was treated as soft in distribution. To verify the electrical design, the realistic wake potential of the 3D structure was calculated using GdfidL and this wake potential was used in the multi-bunch simulations.
* M. Borland et al., "Planned Use of Pulsed Crab Cavities at the APS for Short X-ray Pulse Generation," these proceedings.** V. Dolgashev et al., "RF Design of Normal Conducting Deflecting Structures for the APS," these proceedings.
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
The University of Texas at Austin, Austin, Texas
Tech-X, Boulder, Colorado
In the classical head-tail chromaticity measurement technique, a single large kick is applied transversely to the beam. The resulting phase difference between the head and the tail is measured and the chromaticity extracted. In the continuous head-tail kicking technique, a very small transverse kick is applied to the beam and the asymptotic phase difference between the head and the tail is found to be a function of chromaticity. The advantage of this method is that since the tune tracker PLL already supplies the small transverse kicks, no extra modulation is required.
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
BNL, Upton, Long Island, New York
Fermilab, Batavia, Illinois
Long-range beam-beam interactions can cause significant degrade of beam quality and lifetime in high energy ring colliders. At RHIC, a series of experiments were carried out to study these effects. In this paper, we report on numerical simulation of the long-range beam-beam interactions at RHIC using a parallel strong-strong particle-in-cell code, BeamBeam3D. The simulation includes nonlinearities from both the beam-beam interactions and the arc sextupoles. We observed significant emittance growth for beam separation below 4 σs under nominal tunes. A scan study in tune space shows strong emittance growth around 7th order resonance. Including the tune modulation due to chromaticity and synchrotron motion shows larger emittance growth than the case without the tune modulation.
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.
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.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne, Illinois
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
In order to characterize the beam-centroid jitter in transverse phase space, sets of position data of the 100-MeV H+ beam and 800-MeV H- beam were taken in the transport lines of the Los Alamos Neutron Science Center (LANSCE) accelerator complex. Subsequent data evaluation produced initially puzzling inconsistencies in the phase-space plots from different pairs of beam-position monitors. It is shown that very small random measurement errors will produce systematic differences between plots that should nominally be identical. The actual beam-centroid jitter and the amount of random error in the measurements can be extracted from the data by performing simulations and determining the parameters for which the resulting plots are consistent with the results from the data. Examples will be shown.
LANL, Los Alamos, New Mexico
Presently, the Los Alamos National Laboratory is in the process of planning a refurbishment of various sub-systems within its Los Alamos Neutron Science Center accelerator facility. A part of this LANSCE facility refurbishment will include some replacement of and improvement to existing older beam diagnostics instrumentation. While plans are still being discussed, some instrumentation that is under improvement or replacement consideration are beam phase and position measurements within the 805-MHz side-coupled cavity linac, slower wire profile measurements, typically known as wire scanners, and possibly additional installation of fast ionization-chamber loss monitors. This paper will briefly describe the requirements for these beam measurements, what we have done thus far to answer these requirements, and some of the technical issues related to the implementation of these instrumentation.
* J. D. Gilpatrick et al. These proceedings.** S. S. Kurennoy and R. E. Shafer, EPAC 2000 (Vienna, Austria, 2000), 1768.
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.
SLAC, Menlo Park, California
LBNL, Berkeley, California
One of the action items for the damping rings of the International Linear Collider (ILC) is to compute the broad-band impedance and, from it, the threshold to the microwave instability. For the ILC it is essential that the operating current be below threshold. Operating above threshold would mean that the longitudinal emittance of the beam would be increased. More seriously, above threshold there is the possibility of time dependent variation in beam properties (e.g. the "sawtooth" effect) that can greatly degrade collider performance. In this report, we present the status of our study including calculations of: an impedance budget, a pseudo-Green's function suitable for Haissinski equation and instability calculations, and instability calculations themselves.
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.
Cockcroft Institute, Lancaster University, Lancaster
UMAN, Manchester
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
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.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
UMAN, Manchester
SLAC, Menlo Park, California
Cockcroft Institute, Warrington, Cheshire
Lancaster University, Lancaster
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
We report on measurements of the transverse wakefields induced by collimators of differing characteristics. An apparatus allowing the insertion of different collimator jaws into the path of a beam was installed in End Station A (ESA) in SLAC. Eight comparable collimator geometries were designed, including one that would allow easy comparison with previous results, and were installed in this apparatus. Measurements of the beam kick due to the collimator wakefields were made with a beam energy of 28.5 GeV, and beam dimensions of ~100 microns vertically and a range of 0.5 to 1.5 mm longitudinally. The trajectory of the beam upstream and downstream of the collimator test apparatus was determined from the outputs of ten BPMs (four upstream and six downstream), thus allowing a measurement of the angular kick imparted to the beam by the collimator under test. The transverse wakefield was inferred from the measured kick. The different aperture designs, data collection and analysis, and initial comparison to theoretical and analytic predictions are presented here.
* "An Apparatus for the Direct Measurement of Collimator Transverse Wakefields", P. Tenenbaum, PAC '99** "Direct Measurement of the Resistive Wakefield in Tapered Collimators", P Tenenbaum, PAC '04
SLAC, Menlo Park, California
The PEP-II B-factory at SLAC has recently experienced unexpected aborts due to anomalously high radiation levels at the BaBar detector. Before the problem was finally traced we performed the wake field analysis of the Q-2 bellows, which is situated at a distance of 2.2 m from the interaction point. Analysis showed that electric field in a small gap between a ceramic tile and metal flange can be high enough to produce sparks or even breakdowns. Later the traces of sparks were found in this bellows.
SLAC, Menlo Park, California
A new Q2-bellows absorber will damp only transverse wake fields and will not produce additional beam losses due to Cherenkov radiation. The design is based on the results of the HOM analysis. Geometry of the slots and absorbing tiles was optimized to get maximum absorbing effect.
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
PPPL, Princeton, New Jersey
This paper makes use of a one-dimensional kinetic model based on the Vlasov-Maxwell equations to describe nonlinear wave and soliton excitations in coasting charged particle beams. The kinetic description makes use of the recently-developed g-factor model [1] that incorporates self-consistently the effects of transverse density profile shape at moderate beam intensities. The nonlinear evolution of wave and soliton excitations is examined for disturbances both moving faster and moving slower than the sound speed, incorporating the important effects of wave dispersion [2]. Analytical solutions are obtained for nonlinear traveling wave pulses with and without trapped particles, and the results of nonlinear perturabtive particle-in-cell simulations are presented that describe the stability properties and long-time evolution.
[1] R. C. Davidson and E. A. Startsev, Phys. Rev. ST Accel. Beams 7, 024401 (2004).[2] R. C. Davidson, Phys. Rev. ST Accel. Beams 7, 054402 (2004).
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.
ANL, Argonne, Illinois
Euclid TechLabs, LLC, Solon, Ohio
We report on the experimental and numerical investigation of beam breakup (BBU) effects in dielectric structures resulting from parasitic wakefields. The experimental program focuses on measurements of BBU in a number of wakefield devices: (a) a 26 GHz power extraction structure; (b) a high gradient dielectric wakefield accelerator; (c) a wakefield structure driven by a high current ramped bunch train for multibunch BBU studies. New beam diagnostics will provide methods for studying parasitic wakefields that are currently unavailable at the AWA facility. The numerical part of this research is based on a particle-Green's function based beam breakup code we are developing that allows rapid, efficient simulation of beam breakup effects in advanced linear accelerators. The goal of this work is to be able to compare the accurate numerical results obtained from the new BBU code with the results of the detailed experimental measurements. An external focusing system for the control of the beam in the presence of strong transverse wakefields is considered.
The beam-beam interaction has a significant impact on the beam emittance growth and the luminosity lifetime in RHIC. A simulation study of the emittance growth was performed using the Lifetrac code. The operational conditions of RHIC 2006 100GeV polarized proton run were used in the study. In this paper, the result of this study is presented and compared to the experimental measurements.
BNL, Upton, Long Island, New York
With 8 arc sextupole families in each RHIC ring, the nonlinear chromaticities can be corrected on-line by matching the off-momentum tunes onto the wanted off-momentum tunes with linear chromaticity only. The Newton method with singular value decomposition (SVD) technique is used for this multi-dimensional nonlinear optimization, where the off-momentum tune response matrix with respect to sextupole strength changes is adopted to simplify and fasten the on-line optimization process. The off-momentum tune response matrix can be calculated with the on-line accelerator optics model or directly measured with the real beam. This correction method will be verified and used in the coming RHIC run'07.