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AAC'04 Agenda
AAC'04 Poster
Organizing Committee
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Invited Plenary Talk
Pietro Musumeci: Very High Energy Gain in the Neptune IFEL experiment
  We report on the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in a 50 cm long undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 micron laser with power larger than 300 GW. The Rayleigh range of the laser, ~1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured in a magnetic spectrometer. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Three-dimensional simulations, in good agreement with the measured electron energy spectrum, indicate that most of the acceleration occurs in the first 25-30 cm of the undulator, corresponding to an energy gradient larger 70 MeV/m. The measured energy spectrum also indicates that higher harmonic IFEL interaction is taking place in the second section of the undulator.
Gerald Dugan: Advanced Accelerator System Requirements Overview
This paper will review the requirements on advanced accelerator systems as applied to next-generation linear colliders. The design issues and requirements for TeV-scale linear colliders will be discussed, and the challenges involved in developing affordable extensions to higher energies, utilizing advanced accelerator concepts, will be presented.
Rami Kishek: Modeling of Halos and Intense Beams *
  How intense a charged particle beam can we transport? The answer depends on our ability to limit deterioration of beam quality from halo formation and other mechanisms of emittance growth. Beam halos in particular introduce other undesirable side effects such as activation of the accelerator structures and increasing background in detectors. So how do halos originate and under what circumstances? A review of halo studies in intense beams is presented with working examples from simulation studies modeling the University of Maryland Electron Ring (UMER).

* This work is funded by US Dept. of Energy grant numbers DE-FG02-94ER40855 and DE-FG02-92ER54178.

John Lewellen: High-Brightness Injector Modeling
  There are many aspects to the successful conception, design, fabrication and operation of high-brightness electron beam sources. Accurate and efficient modeling of the injector are critical to all phases of the process, from evaluating initial ideas to successful diagnosis of problems during routine operation. The basic modeling tasks will vary from design to design, according to the basic nature of the injector (dc, rf, hybrid, etc.), the type of cathode used (thermionic, photo, field emission, etc.) and "macro" factors such as average beam current and duty factor, as well as the usual list of desired beam properties. The injector designer must be at least aware of, if not proficient at addressing, the multitude of issues which arise from these considerations; and, as high-brightness injectors continue to move out of the laboratory and into the user facility or instrument, the number of such issues will continue to expand.

This talk will begin with a general discussion of injector modeling philosophy, and a review of some of the "standard" codes used for rf-based designs. Next, some of the issues related to transitioning a high-brightness injector from laboratory instrument to subcomponent status will be considered within the context of performance modeling. The talk concludes with a discussion of potential future paths, emphasizing multiphysics modeling and more-integrated design.

Simon Hooker: Review of laser guiding experiments
  A common requirement for all laser-driven plasma accelerators is the propagation of one or more intense beams of radiation through a plasma. The distance over which the driving laser maintains an intensity close to the focal intensity is a significant factor determining the acceleration that is achieved. In the absence of any method to guide the laser radiation, the laser-plasma interaction length is limited by diffraction to the order of the Rayleigh range, which for the laser parameters of interest is typically only a few millimetres. In this talk we describe and explain the operation of waveguides able to channel laser pulses with intensities greater than 10^16 W/cm^2 over lengths significantly longer than the Rayleigh range. These include: grazing-incidence guiding, relativistic channelling, and several types of plasma waveguide. For each technique the recent experimental work will be reviewed and their prospects for application to laser-driven accelerators assessed.
Igor Pogorelsky: Gas lasers for strong field applications
  We review a diverse field of the gas laser technology. Gas lasers cover a spectral range from UV to Far-IR and are capable to produce diffraction limited beams of the kilowatt and even megawatt average power and wall plug efficiency up to 70%. Atomic, molecular and excimer lasers employ a variety of pumping schemes including electric discharge, electron beams, optical and chemical pumping. Among these lasers, we identify available options and possible candidates for producing relativistically strong (a>1) pico- and femtosecond pulses. We review several ongoing projects in this field. Special attention is given to picosecond CO2 lasers that proved to be a valuable tool for strong-field physics applications. Several advanced accelerator schemes benefit from a long wavelength (lambda=10 um) of the CO2 lasers. This facilitates structure-based accelerators, production of micro-bunches and their re-phasing to the laser field. The last feature is important for demonstrating monoenergetic and multi-staged electron acceleration. Ponderomotive energy of the electron in the laser field is proportional to the lambda squared that can be utilized in the plasma based schemes, ion acceleration, Thomson scattering, and other processes. Finally, we will analyze possibilities for generating CO2 laser pulses of the petawatt peak power and a-few-cycles duration.
Marc Ross: Diagnostics for High Energy Accelerators
  High energy accelerators face two frontiers, both related to the need to increase luminosity in order to have a constant event rate. First is the requirement for extreme precision, beyond that which would have been labelled ridiculous a generation ago. Second is the requirement to operate with very high power beams. Typical values for these parameters at the proposed linear collider are 1 micron beam size and 10 MW beam power. A beam profile monitor with 1% resolution must therefore be able to distinguish a 1.01 um beam from a 1.00 micron beam, a difference of only a few atomic diameters. These Diagnostics are used to ensure operation at the highest possible collider luminosity. This is done with a combination of clever ideas, brute force conservative engineering and insightful operational considerations. In addition to the above, the wealth of information from the monitors must be redirected back to the beam as directly as possible using automatic feedback schemes. Instrumentation and feedback projects are ideal for small groups with students because of their intrinsic small size and fascinating basic physics and hardware. Both the ATF at BNL and the ATF at KEK have been key in the development of new instrumentation.
Mitsuru Uesaka: Femtosecond Beam Sources and Applications
  Short particle beam science has been promoted by electron linac and radiation chemistry up to picoseconds. Recently, table-top TW laser enables several kinds of short particle beams and pump-and-probe analyses. 4th generation SR sources aim to generation and application of about 100 fs X-ray. Thus, femtosecond beam science has become one of the important field in advanced accelerator concepts. By using electron linac with photoinjector, about 200 fs single bunch and 3 fs multibunchs are available. Tens femtoseconds monoenergetic electron bunch is expected by laser plasma cathode. Concerning the electron bunch diagnosis, we have seen remarkable progress in streak camera, coherent radiation spectroscopy, fluctuation method and E/O crystal method. Picosecond time-resolved pump-and-probe analysis by synchronizing electron linac and laser is now possible, but the timing jitter and drift due to several fluctuations in electronic devices and environment are still in picoseconds. On the other hand, the synchronization between laser and secondary beam is done passively by an optical beam-splitter in the system based on one TW laser. Therefore, the timing jitter and drift do not intrinsically exist there. The author believes that the femtosecond time-resolved pump-and-probe analysis must be initiated by the laser plasma beam sources. As to the applications, picosecond time-resolved system by electron photoinjector/linac and femtosecond laser are operating in more than 5 facilities for radiation chemistry in the world. Ti:Sapphire-laser-based repetitive pump-and-probe analysis started by time-resolved X-ray diffraction to visualize the atomic motion. Nd:Glass-laser-based single-shot analysis was performed to visualize the laser ablation via the single-shot ion imaging. The author expects that protein dynamics and ultrafast nuclear physics would be the next interesting targets. Monograph titled gFemtosecond Beam Scienceh is published by Imperial College Press in 2004.
Santiago Bernal: The University of Maryland Electron Ring: a model recirculator for intense-beam physics research
  The University of Maryland Electron Ring (UMER), designed for transport studies of space-charge dominated beams in a strong focusing lattice, is nearing completion. Low energy, high intensity electron beams provide an excellent model system for experimental studies with relevance to all areas that require high quality, intense charged-particle beams. In addition, UMER constitutes an important tool for benchmarking of computer codes. When completed, the UMER lattice will consist of 36 alternating-focusing (FODO) periods over an 11.5-m circumference. Current studies in UMER over about 2/3 of the ring include beam-envelope matching, halo formation, unsymmetrical focusing, and longitudinal dynamics (beam bunch erosion and wave propagation.) Near future, multi-turn operation of the ring will allow us to address important additional issues such as resonance-traversal, energy spread and others. The main diagnostics are phosphor screens and capacitive beam position monitors placed at the center of each 20-degree bending section. In addition, pepper-pot and slit-wire emittance meters are in operation. The range of beam currents used correspond to space charge tune depressions from 0.2 to 0.8, which is unprecedented for a circular machine.
Yoneyoshi Kitagawa: Review of Advanced Accelerator Concepts R & D in Japan
  Since Tajima and Dawson have proposed the concept of the laser accelerator in1979, Japan has been devoting much efforts to not only realizing the advanced laser accelerator, but also making the current accelerators compact in scale. As for the electron acceleration, the Kitagawa group, Osaka University, has achieved the capillary-guided acceleration of electrons to 100 MeV via the laser wake field. The 1 cm long glass capillary confined a plasma of 6x10^16 cm^-3 over 1 cm. They apply their PW laser to the particle acceleration. The Uesaka group, University of Tokyo, once generated hot electrons via the wave-breaking field in the prepulse at the gas jet edge. They call it the plasma cathode. Hence the main pulse wakefield accelerated them to 40 MeV. The Koyama group, National Institute of Advanced Industrial Science and Technology, observed non-Maxwellian electron peaks at 7 MeV via the Raman scattering. For the ion acceleration, The Daido group, Japan Atomic Energy Research Institute APR, studied the proton acceleration in the underdense plasma. The Ogata group, Hiroshima University and the Nemoto group, Central Research Institute of Electric Power Industry, worked with the neutral beam and ion generation via thin films. The Ogata group is trying the photonic crystal acceleration, too. The Nishida and Yugami group, Utsunomiya University, found the 200 GHz radiation under a magnetized plasma. As for the advanced rf accelerator, the Urakawa group, KEK, developed the new photo-rf electron gun: 20 bunch in 10 ps pulse 5 pimm mrad at 12.5 Hz. The Japan Synchrotron Radiation Research Institute SPring-8 and the Himeji Institute of Technology groups are also active in the photo rf cathodes. As well, we look around the Asian community activities. Korea, Taiwan, China, India and Israel have been greatly grown in recent years to reach the world-class cutting edge in this field.
Warren Mori: Advances in simulation capability: A path towards full-scale modeling of 10 GeV–100 GeV plasma-based accelerator stages
  Modeling plasma-based accelerators is a great challenge. These challenges arise because of the need to accurately describe three processes: the evolution of a laser or particle beam through long regions of plasma, the generation of the plasma wakefields that are generated, the acceleration and beam loading of an intense trailing bunch of particles. While fluid codes can model important pieces of the problem, to include all of the above processes will require particle-based methods. Using fully explicit particle-in-cell methods, requires ~5000 (particle beam driver) to ~100,000 (laser driver) CPU hours on today’s fastest computers to model each GeV gain in energy. Clearly, it would be impractical to use this method to model 10 – 100 GeV stages. In this talk I will describe recent advances in modeling plasma-based accelerators using particle-in-cell (PIC) methods. I will emphasize the recent development of a fully three-dimensional, fully parallelized, quasi-static PIC code called QuickPIC that can model both laser driven and plasma driven schemes including beam loading. I will show that when all of the quasi-static equations are included this method can reproduce the full PIC results and provide a factor of 100-500 in computational savings. I will show preliminary results from QuickPIC on the propagation of the 50 GeV SLC beam through meters of plasma. I will also briefly discuss how the plasma based methods are impacting conventional accelerator issues and I will describe recent advances in full PIC modeling, emphasizing the science results.through meters of plasma. I will also describe recent advances in full PIC modeling, emphasizing the science results.