Vanderbilt University, Nashville, Tennessee
DESY, Hamburg
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.
INFN/LNF, Frascati (Roma)
UCLA, Los Angeles, California
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.
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.
ACCEL, Bergisch Gladbach
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
An intense L-band electron accelerator is now being installed at PAL (Pohang Accelerator Laboratory) for initial tests. It is capable of producing 10-MeV electron beams with average 30 kW. This accelerator has a diode-type E-gun, a pre-buncher cavity, and an accelerating column with the built-in bunching section. We conduct simulational study for the commissioning scenario by the PARMELA code. At first, we observe the beam position and the beam current when the beam line is misaligned under no fields. Next, turning on focusing solenoids we observe the beam position change to check the alignments of the solenoids. Finally, varying RF power and phase of the pre-buncher we observe beam energy and beam power to obtain the optimum pre-buncher condition. In this paper, we present simulational results for each step. We also present commissioning strategies based on these results.
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
For a compact X-ray source, we designed a C-band standing-wave electron accelerator. It is capable of producing 4-MeV electron beams with 50-mA peak beam current. As an RF source, we use 5-GHz magnetron with duty factor of 0.08%. The accelerating structure is bi-periodic and on-axis coupled structure, operated with π/2-mode standing waves. Each cavity in the bunching and normal cell is designed by the MWS code and measured with aluminium prototype cavity. As per the dispersion relation derived from the measurement results, calibration factor obtained for the actual copper cavity.
SLAC, Menlo Park, California
A train of 2-nsμbunches are generated in the DC-gun based injector in the ILC e- source; a bunching system with extremely high bunching efficiency to compress bunch down to 20 ps FWHM is designed. Complete optics to transport the electron beam to the 5-GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the bunching system, pre-acceleration, chicane, 5-GeV SC booster linac, spin rotators and energy compressor. It shows more than 95% of electrons from the DC-gun are captured within the 6-D damping ring acceptance at the entrance of damping ring injection line. The field and alignment errors, and orbit correction are analyzed.
Fermilab, Batavia, Illinois
JINR, Dubna, Moscow Region
Presently the Fermilab Booster can accomodate about half the maximum proton beam intensity which the Linac can deliver. One of the limitations is related to large vertical tuneshift produced by space-charge forces at injection energy. In the present report we study the nonlinear beam dynamics in the presence of space charge and magnet imperfections and analyze the possibility of space charge compensation with electron lenses.
PPPL, Princeton, New Jersey
UCB, Berkeley, California
LBNL, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
Future warm dense matter experiments with space-charge dominated ion beams require simultaneous longitudinal bunching and transverse focusing. The challenge is to longitudinally bunch the beam two orders of magnitude to a pulse length shorter than the target disassembly time and focus the beam transversely to a sub-mm focal spot. An experiment to simultaneously focus a singly charged potassium ion beam has been carried out at LBNL. The space charge of the beam must be neutralized so only emittance limits the simultaneous focusing. An induction bunching module provides a head-to-tail velocity ramp upstream of a plasma filled drift section. Tuning the initial beam envelope to compensate for the defocusing of the bunching module enables simultaneous focusing. A comparison of experimental and calculated results are presented, including the transverse distribution and the longitudinal phase-space of the beam.
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.