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| TPPE051 | The Optimization of the Electron Injector Resonance System Based on the Evanescent Oscillations | electron, simulation, emittance, space-charge | 3170 | ||
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The report presents the results of the bunching system optimization and electrons motion simulation in the compact S – band injector. The injector consists of the low-voltage diode electron gun and optimized bunching system based on the resonant system with the evanescent oscillations. The amplitude of RF electrical field is increased along the axis of the bunching system. The resonance system optimization allows to obtain electron bunches with the phase length less than 10° (for 70 % particles) at the injector exit.
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| TPPP047 | New and Efficient Neutrino Factory Front-End Design | target, proton, factory, linac | 2986 | ||
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Funding: Work supported by U.S. Department of Energy. |
As part of the APS Joint Study on the Future of Neutrino Physics* we have carried out detailed studies of the Neutrino Factory front-end. A major goal of the new study was to achieve equal performance to our earlier feasibility studies** at reduced cost. The optimal channel design is described in this paper. New innovations included an adiabatic buncher for phase rotation and a simplified cooling channel with LiH absorbers. The linear channel is 295 m long and produces 0.17 muons per proton on target into the assumed accelerator transverse acceptance of 30 mm and longitudinal acceptance of 150 mm. *APS Multi-Divisional Study of the Physics of Neutrinos, http://www.aps.org/neutrino/. **S.Ozaki, R.B.Palmer, M.Zisman and J.C.Gallardo, edts., Tech. Rep., BNL-52623 (2001), http://www.cap.bnl.gov/mumu/studyii/FS2-report.html. |
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| WPAP009 | Optimization of RF Compressor in the SPARX Injector | emittance, brightness, simulation, gun | 1144 | ||
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The SPARX photoinjector consists in a rf gun injecting into three SLAC accelerating sections, the first one operating in the RF compressor configuration in order to achieve higher peak current. A systematic study based on PARMELA simulations has been done in order to optimize the parameters that influence the compression also in view of the application of this system as injector of the so called SPARXINO 3-5 nm FEL test facility. The results of computations show that peak currents at the injector exit up to kA level are achievable with a good control of the transverse and longitudinal emittance by means of a short SW section operating at 11424 MHz placed before the first accelerating section. Some working points in different compression regimes suitable for FEL experiments have been selected. The stability of these points and the sensitivity to various types of random errors are discussed.
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| WPAT030 | Upgrade of the ATLAS Positive Ion Injector Bunching System | feedback, ion, pick-up, linac | 2161 | ||
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Over the last few years, significant efforts were concentrated on improving the ATLAS Positive Ion Injector (PII) RF bunching system, consisting of a four-harmonic pre-buncher, Traveling Wave Chopper (TWC) and a single-frequency sinusoidal re-buncher. The primary goal was to improve RF field stability with a redesigned RF system and to improve buncher performance for higher current beams resulting in better bunch stability and time structure at the first PII superconducting resonator. The major parts of the system were redesigned and rebuilt, including the RF 12 – 48 MHz amplifiers for the harmonic pre-buncher and re-buncher, RF driver rack for the TWC, and the RF control chassis for both the pre-buncher and re-buncher. The four-harmonic resonant structure of the harmonic buncher itself was modified, too, mainly for better mechanical stability and better RF matching. These improvements will be described and the performance of the new system presented.
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| WPAT080 | Calculation of Beam-Loaded Q in High-Power Klystrons | gun, klystron, vacuum, cathode | 4060 | ||
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Funding: Work supported by DOE SBIR Grant DE-FG02-03ER83776. |
Instabilities in the gun region of a high-power klystron can occur when there is positive feedback between a mode and an induced current on the quasi-steady state beam emitted by the gun cathode.* This instability is dependent on the gun voltage, is predicted on the basis of a negative beam-loaded Q. The established method for computing the beam-loaded Q of a cavity involves using a time-dependent electromagnetic particle-in-cell (PIC) code to track beam particles through the quasi-static gun fields perturbed by the electromagnetic fields of a cavity eigenmode.** The energy imparted to the beam by the mode is obtained by integrating the Lorentz force along the particle tracks, and this quantity is simply related to the beam-loaded Q. We have developed an alternative approach that yields comparable accuracy but is computationally much simpler. The new method is based on a much simpler time-independent electrostatic PIC calculation, resulting in much faster solutions without loss of accuracy. We will present the theory and implementation of the new method, as well as benchmarks and results from analysis of the XP-4 klystron that show a potential instability near 3 GHz. *B. Krietenstein, et al., "Spurious oscillations in high-power klystrons," PAC95, 1995. **U. Becker, et al., "Simulation of oscillations in high-power klystrons," EPAC, 1996. |
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| RPAE017 | Radially Polarized Ion Channel Laser | ion, radiation, betatron, electron | 1526 | ||
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Radially polarized radiation is amplified by a free electron laser (FEL) in which the undulator is an ion channel with uniform density. For long betatron wavelengths and low gain per pass, the gain at a given distance from the axis is three-eighths the gain of a periodic ion channel laser with the same wiggler parameter. For amplification of short wavelengths by an ultrarelativistic electron beam, a uniform-density ion channel requires a much higher ion density than a periodic ion channel laser.
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| RPPT002 | Harmonic Content of the BESSY FEL Radiation | radiation, undulator, electron, simulation | 829 | ||
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Funding: Funded by Zukunftsfonds Berlin. |
BESSY proposes a linac-based cascaded High-Gain Harmonic-Generation (HGHG) free electron laser (FEL) multi-user facility. The BESSY soft X-ray FEL will consist of three undulator lines. The associated tunable lasers will cover the spectral range of 230nm to 460nm. Two to four HGHG stages reduce the seed wavelength to the desired radiation range of 1.24nm < λ < 51nm. The harmonic content of the high-intensity radiator output can be used to reduce the number of necessary HGHG stages. Moreover the higher harmonic content of the final output extends the offered spectral range and thus is of high interest for the user community. In this paper, the higher harmonic content of the final output as well as of the output of several radiators are investigated. The main parameters such as output power, pulse duration and bandwidth as well as their suitability for seeding are discussed. |
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| RPPT021 | Inducing Strong Density Modulation with Small Energy Dispersion in Particle Beams and the Harmonic Amplifier Free Electron Laser | electron, radiation, undulator, emittance | 1718 | ||
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Funding: We acknowledge the support of the European Union's EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance. |
We present a possible method of inducing a periodic density modulation in a particle beam with little increase in the energy dispersion of the particles. The flow of particles in phase space does not obey Liouville's Theorem. The method relies upon the Kuramoto-like model of collective synchronism found in free electron generators of radiation, such as Cyclotron Resonance Masers and the Free Electron Laser. For the case of an FEL interaction, electrons initially begin to bunch and emit radiation energy with a correlated energy dispersion which is periodic with the FEL ponderomotive potential. The relative phase between potential and particles is then changed by approximately 180 degrees. The particles continue to bunch, however, there is now a correlated re-absorption of energy from the field. We show that, by repeating this relative phase change many times, a significant density modulation of the particles may be achieved with only relatively small energy dispersion. A similar method of repeated relative electron/radiation phase changes is used to demonstrate supression of the fundamental growth in a high gain FEL so that the FEL lases at the harmonic only. |
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| FPAE009 | Bunched Beam Cooling in the Fermilab Recycler | emittance, synchrotron, collider, scattering | 1153 | ||
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Stochastic cooling with bunched beam in a linear bucket has been obtained and implemented operationally in the fermilab recycler. In this implementation the particle bunch length is much greater than the cooling system wavelengths. The simultaneous longitudinal bunching enables cooling to much smaller longitudinal emittances than the coasting beam or barrier bucket system. Characteristics and limitations of bunched beam stochastic cooling are discussed.
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| FPAT042 | Beam Dynamics and Pulse Duration Control During Final Beam Bunching in Driver System for Heavy Ion Inertial Fusion | lattice, emittance, focusing, beam-transport | 2735 | ||
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Beam dynamics is investigated by multi-particle simulations during a final beam bunching in a driver system for heavy ion inertial fusion (HIF). The longitudinal bunch compression causes the beam instability induced by the strong space charge effect. The multi-particle simulation can indicate the emittance growth due to the longitudinal bunch compression. Dependence in the beam pulse duration is also investigated for effective pellet implosion in HIF. Not only the spatial nonuniformity of the beam illumination, but also the errors of the beam pulse duration cause changes of implosion dynamics. The allowable regime of the beam pulse duration for the effective fusion output becomes narrow with decreasing the input beam energy. The voltage accuracy requirement at the beam velocity modulator is also estimated for the final beam bunching. It is estimated that the integrated voltage error is allowable as a few percent.
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