• M. Ferrario
  
• D. Alesini, M. Bellaveglia, S. Bertolucci, R. Boni, M. Boscolo, M. Castellano, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, A. Esposito, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, M. Incurvati, C. Ligi, M. Migliorati, A. Mostacci, E. Pace, L. Palumbo, L. Pellegrino, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, F. Tazzioli, S. Tomassini, C. Vaccarezza, M. Vescovi, C. Vicario
  INFN/LNF, Frascati (Roma)
• A. Bacci, S. Cialdi, A. R. Rossi, L. Serafini
  INFN-Milano, Milano
• L. Catani, E. Chiadroni, A. Cianchi
  INFN-Roma II, Roma
• A. M. Cook, M. P. Dunning, P. Frigola, J. B. Rosenzweig
  UCLA, Los Angeles, California
• L. Giannessi, M. Quattromini, C. Ronsivalle
  ENEA C. R. Frascati, Frascati (Roma)
• P. Musumeci, M. Petrarca
  INFN-Roma, Roma

• T. Shintake
  

• H. Toyokawa
  
• H. Ikeura-Sekiguchi, M. K. Koike, R. Kuroda, H. Ogawa, N. Sei, M. Tanaka, K. Y. Yamada, M. Y. Yasumoto
  AIST, Tsukuba, Ibaraki
• T. Nakajyo, F. Sakai, T. Y. Yanagida
  SHI, Tokyo

• U. B. Blell
  
• A. V. Batrakov, S. A. Onischenko, G. E. Ozur
  Institute of High Current Electronics, Tomsk
• J. Florenkowski, U. Kopf, C. Muehle, M. Petryk, I. J. Petzenhauser, P. J. Spiller
  GSI, Darmstadt

• A. Bonucci
  
• A. Conte, P. Manini, S. Raimondi
  SAES Getters S.p. A., Lainate

• A. Conte
  
• A. Bonucci, P. Manini, S. Raimondi
  SAES Getters S.p. A., Lainate

• S. Ohsawa
  
• Y. Hozumi
  Advanced Manufacturing Research Institute, Tsukuba
• M. Ikeda, T. Sugimura
  KEK, Ibaraki

• H. Ohgaki
  
• T. Kii, K. Masuda, T. Yamazaki, K. Yoshikawa, H. Zen
  Kyoto IAE, Kyoto

• D. R. Walters
  

A prototype vacuum chamber is under development at the Advanced Photon Source for use in the Linac Coherent Light Source at Stanford Linear Accelerator Center. The chamber will be fabricated from the austenite stainless steels. The chamber requires a continuous aluminum coating on the inner surface in order to reduce the wakefield losses to a level within the resistivity budget. The method being presented here is unique in that it can be applied to a fully fabricated chamber 5 mm high, 11.5 mm wide, and 3460 mm long. In existing methods the chamber aperture has been much larger than is used here. This paper describes a method applicable for these smaller cross sections. This process uses a pair of small electrodes, centered in the aperture, where they are attached to a high frequency AC power supply. In this configuration each electrode is connected to the opposite polarity of the other. The chamber cavity is filled with argon gas to facilitate the formation of a glow discharge causing the aluminum electrodes to sputter onto the chamber walls. This paper presents the laboratory test results from small samples up to the full-sized assemblies.

• J. Ruan
  
• H. Edwards, R. P. Fliller, J. K. Santucci
  Fermilab, Batavia, Illinois

The current Fermilab A0 Photoinjector laser system includes a seed laser, a flashlamp pumped multipass amplifier cavity, a flashlamp pumped 2-pass amplifier system followed by an IR to UV conversion stage. However the current system can only deliver up to 800 pulses due to the low efficiency of Nd:Glass used inside multi-pass cavity. In this paper we will report the effort to develop a new multi pass cavity based on Nd:YLF crystal end-pumped by diode laser. We will also discuss the foreseen design of the laser system for the NML accelerator test facility at Fermilab.

• J. J. Petillo
  
• K. Jensen, B. Levush
  NRL, Washington, DC
• J. N. P. Panagos
  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.

• J. S. Sekutowicz
  
• M. Ferrario
  INFN/LNF, Frascati (Roma)
• J. Iversen, D. Klinke, D. Kostin, W.-D. Moller, A. Muhs
  DESY, Hamburg
• P. Kneisel
  Jefferson Lab, Newport News, Virginia
• K. Ko, Z. Li, L. Xiao
  SLAC, Menlo Park, California
• R. S. Lefferts, A. R. Lipski
  SBUNSL, Stony Brook, New York
• T. Rao, J. Smedley
  BNL, Upton, Long Island, New York
• P. Strzyzewski
  The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock

• S. Lederer
  
• G. Asova, J. W. Baehr, C. H. Boulware, H.-J. Grabosch, M. Hanel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, B. Petrosyan, S. Rimjaem, T. A. Scholz, L. Staykov, F. Stephan
  DESY Zeuthen, Zeuthen
• K. Boyanov
  INRNE, Sofia
• L. H. Hakobyan
  YerPhI, Yerevan
• P. Michelato, L. Monaco, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)
• R. Richter
  BESSY GmbH, Berlin
• J. Roensch
  Uni HH, Hamburg

Beginning 2007, a new gun cavity will be installed at the photo injector test facility at DESY in Zeuthen (PITZ). It will be conditioned towards gradients as high as 60 MV/m. This gradient is required for the operation of the European XFEL. Results from the conditioning for high peak power and high duty cycle will be reported.

• G. D'Auria
  
• D. Bacescu, L. Badano, F. Cianciosi, P. Craievich, M. B. Danailov, G. Penco, L. Rumiz, M. Trovo, A. Turchet
  ELETTRA, Basovizza, Trieste
• H. Badakov, A. Fukasawa, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California

• C. Ronsivalle
  
• A. Bacci, A. R. Rossi, L. Serafini
  INFN-Milano, Milano
• M. Boscolo, E. Chiadroni, M. Ferrario, D. Filippetto, V. Fusco, G. Gatti, M. Migliorati, A. Mostacci, C. Vaccarezza, C. Vicario
  INFN/LNF, Frascati (Roma)
• A. Cianchi
  INFN-Roma II, Roma
• L. Giannessi, M. Quattromini
  ENEA C. R. Frascati, Frascati (Roma)
• M. Petrarca
  Universita di Roma I La Sapienza, Roma

• G. Gatti
  
• L. Cultrera, F. Tazzioli
  INFN/LNF, Frascati (Roma)
• J. Moody, P. Musumeci
  UCLA, Los Angeles, California
• A. Perrone
  INFN-Lecce, Lecce

• C. Vicario
  
• M. Bellaveglia, D. Filippetto, A. Gallo, G. Gatti, A. Ghigo
  INFN/LNF, Frascati (Roma)
• S. Cialdi
  INFN-Milano, Milano
• P. Musumeci, M. Petrarca
  INFN-Roma, Roma

• K. Togawa
  
• A. Higashiya, T. Shintake
  RIKEN Spring-8 Harima, Hyogo

• T. Gowa
  
• H. Hayano, J. Urakawa
  KEK, Ibaraki
• Y. Kamiya, A. Masuda, R. Moriyama, K. Sakaue, M. Washio
  RISE, Tokyo
• S. Kashiwagi
  ISIR, Osaka
• R. Kuroda
  AIST, Tsukuba, Ibaraki
• K. U. Ushida
  RIKEN, Saitama

At Waseda University, we have succeeded in generating soft X-rays based on laser Compton scattering. The energies are within "Water Window" part (250~500eV) where the X-ray absorption coefficient of water is much less than that of constituent elements of living body such as carbon, hydrogen and nitrogen. For this reason, it is expected to apply to a bio-microscope with which we can observe living cells without dehydration. To improve the generation system, we remodeled our collision chamber and adopted 3-pass flash lamp amplifier system. With these modifications, we achieved high S/N ratio. The photon number detected by MCP was 278/pulse, tenfold increase of that in last year. Moreover, we succeeded in generating soft X-rays stably for more than 10 hours. Now we are planning to measure two-dimensional distribution of the X-rays by CCD. In this conference, experimental results and future plans will be reported.

• Y.-C. Du
  
• W.-H. Huang, Y. Lin, C.-X. Tang, D. Xiang, L. X. Yan
  TUB, Beijing

This work was supported by the Chinese National Foundation of Natural Sciences under Contract no. 10645002.

• D. Xiang
  
• Y.-C. Du, W.-H. Huang, R. K. Li, Y. Lin, C.-X. Tang, L. X. Yan
  TUB, Beijing
• J. H. Park, S. J. Park
  PAL, Pohang, Kyungbuk

There are growing interests in generation, preservation and applications of high brightness electron beam. With the rapid development in the techniques for emittance compensation and laser shaping, we are approaching the limit-the uncorrelated thermal emittance. In this paper, we report the measurements of thermal emittance for Cu and Mg. The measurement is conducted in a field-free region. The energy spectrum and angular distribution of the electrons are measured immediately after its emission and further used to reconstruct the initial phase space and the corresponding thermal emittance. We also show how cathode surface roughness* and laser incidence angle as well as its polarization state** affect the quantum efficiency and thermal emittance.

*X. Z. He, High energy physics and nuclear physics,28(2004)1007.**Dao Xiang,et al, NIM A,562(2006)48.

• A. P. Lee
  
• S.-S. Chang, J.-Y. Hwang, W. K. Lau, C. C. Liang, G.-H. Luo, T.-T. Yang
  NSRRC, Hsinchu

• J. W. McKenzie
  
• B. L. Militsyn
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• A. S. Terekhov
  ISP, Novosibirsk

• V. D. Shiltsev
  

• E. J. Montgomery
  
• D. W. Feldman, N. A. Moody, P. G. O'Shea, Z. Pan
  UMD, College Park, Maryland
• K. Jensen
  NRL, Washington, DC

Photocathodes for high power free electron lasers face significant engineering and physics challenges in the quest for efficient, robust, long-lived, prompt laser-switched operation. The most efficient semiconductor photocathodes, notably those responsive to visible wavelengths, suffer from poor lifetime due to surface layer degradation, contamination, and desorption. Using a novel dispenser photocathode design, rejuvenation of cesiated surface layers in situ is investigated for semiconductor coatings building on previous results for cesiated metals. Cesium from a sub-surface reservoir diffuses to the surface through a microscopically porous, sintered tungsten matrix to repair the degraded surface layer. The goal of this research is to engineer and demonstrate efficient, robust, long-lived regenerable photocathodes in support of predictive photocathode modeling efforts and suitable for photoinjection applications.

• C. K. Sinclair
  
• I. V. Bazarov, B. M. Dunham, Y. Li, X. G. Liu, D. G. Ouzounov
  Cornell University, Department of Physics, Ithaca, New York
• F. E. Hannon
  Cockcroft Institute, Lancaster University, Lancaster
• T. Miyajima
  KEK, Ibaraki

Recent computational optimizations have demonstrated that it should be possible to construct electron injectors based on photoemission cathodes in very high voltage DC electron guns in which the beam emittance is dominated by the thermal emittance from the cathode. Negative electron affinity photocathodes have been shown to have a naturally low thermal emittance. However, the thermal emittance depends on the illuminating wavelength; the degree of negative affinity; and the band structure of the photocathode material. As part of the development of a high brightness, high average current photoemission electron gun for the injector of an ERL light source, we have measured the thermal emittance from negative affinity GaAs and GaAsP photocathodes. The measurements were made by measuring the electron beam spot size downstream of a counter-wound solenoid lens as a function of the lens strength. Electron beam spot sizes were measured by two techniques - a 20 micron wire scanner, and a CVD diamond screen. Both Gaussian and 'tophat' spatial profiles were used, and measurements were made at several wavelengths. Results will be presented for both cathode types.

• C. K. Sinclair
  
• I. V. Bazarov, B. M. Dunham, Y. Li, X. G. Liu
  Cornell University, Department of Physics, Ithaca, New York
• K. W. Smolenski
  CLASSE, Ithaca

We have constructed a very high voltage photoemission electron gun as the electron source of a high brightness, high average current injector for an energy recovery linac (ERL) synchrotron radiation light source. The source is designed to deliver 100 mA average current in a CW 1300 MHz pulse train (77 pC/bunch). The cathode voltage may be as high as 750 kV. Negative electron affinity photocathodes are employed to obtain small thermal emittances. The electrode structure is assembled without touching any electrode surface. A load-lock system allows cleaning and activation of cathode samples prior to installation in the electron gun. Cathodes are cleaned by heating and exposure to atomic hydrogen, and activated with cesium and nitrogen trifluoride. Two cathode electrode sets, of 316LN stainless steel and Ti4V6Al alloy, have been used. The anode is beryllium. The internal surface of the ceramic insulator of the gun has a high resistivity fired coating, providing a path to drain away charge from field emission. Non-evaporable getters provide a very high pumping speed for hydrogen. Operating experience with this gun will be presented.

• S. G. Anderson
  
• H. Badakov, P. Frigola, A. Fukasawa, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California
• C. P.J. Barty, D. J. Gibson, F. V. Hartemann, M. J. Messerly, M. Shverdin, C. Siders, A. M. Tremaine
  LLNL, Livermore, California

Compton scattering of intense laser pulses with ultra-relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free-electron lasers and laser and plasma based advanced accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described and transverse phase space measurements are presented.

• A. Fukasawa
  
• S. G. Anderson
  LLNL, Livermore, California
• H. Badakov, E. Hemsing, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California

• J. Bisognano
  
• R. A. Bosch, M. A. Green, K. Jacobs, K. J. Kleman, R. A. Legg
  UW-Madison/SRC, Madison, Wisconsin
• J. Chen, W. Graves, F. X. Kaertner, J. Kim
  MIT, Cambridge, Massachusetts

We present an initial design of the driver for the Wisconsin VUV/Soft Xray FEL facility, which will provide high intensity coherent photons from 5 eV to 1.2 keV. It uses a 2.5 GeV, L-band CW superconducting linac with a 1.7 GeV tap-off to feed the lower energy FELs. In order to support multiple high rep-rate FELs, the average design current is 1 mA. Sub-nanocoulomb bunches with normalized transverse emittances of order 1 micron are generated in a photoinjector for beamlines operating at repetition rates from kHz to MHz. Multi-stage bunch compression provides 1 kA peak current to the FELs, with low energy spread and a suitable current profile. Compressed bunch lengths of several hundred femtoseconds will allow generation of photon pulses in the range 10 to 100 fs using cascaded FELs. Consideration has been given to removing the residual energy chirp from the beam, and minimizing the effects of space charge, coherent synchrotron radiation, and microbunching instabilities. A beam switchyard using RF separators and fast kickers delivers the desired electron bunches to each of the FELs. Details of the design will be presented, including those areas requiring the most development work.

• D. Dowell
  
• E. N. Jongewaard, J. R. Lewandowski, Z. Li, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks, J. W. Wang, L. Xiao
  SLAC, Menlo Park, California

The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at GTF at SLAC, SDL and ATF at BNL and other laboratories, the 1.6cell s-band (2856MHz) gun was chosen to be the best electron source for the LCLS injector, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce nearly-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120Hz and a 140MV/m cathode field, or to an average power dissipation of 4kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results and analysis of these high-power tests will be presented.

• D. Dowell
  
• E. N. Jongewaard, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks
  SLAC, Menlo Park, California

The field emission was measured during the high-power testing of the LCLS photocathode RF gun. A careful study and analysis of the field emission electrons, or dark current is important in assessing the gun's internal surface quality in actual operation, especially those surfaces with high fields. The charge per 2 microsecond long RF pulse (the dark charge) was measured as a function of the peak cathode field for the 1.6 cell, 2.856GHz LCLS RF gun. Faraday cup data was taken for cathode peak RF fields up to 120MV/m producing a maximum of 0.6nC/RF pulse for a diamond-turned polycrystalline copper cathode installed in the gun. The field dependence of the dark charge is analyzed using a temperature-dependent Fowler-Nordheim (FN) theory to obtain the field enhancement factor and other emitter parameters. Digitized images of the dark charge were taken using a 100 micron thick YAG crystal for a range of solenoid fields to determine the location and angular distribution of the field emitters. The FN plots and emitter image analysis will be described in this paper.

• P. Emma
  
• R. Akre, J. Castro, Y. T. Ding, D. Dowell, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, P. Krejcik, C. Limborg-Deprey, H. Loos, A. Miahnahri, C. H. Rivetta, M. E. Saleski, J. F. Schmerge, D. C. Schultz, J. L. Turner, J. J. Welch, W. E. White, J. Wu
  SLAC, Menlo Park, California
• L. Froehlich, T. Limberg, E. Prat
  DESY, Hamburg

The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive-laser and RF photocathode gun through the first bunch compressor chicane, was installed during the Fall of 2006. Initial system commissioning with an electron beam takes place in the Spring and Summer of 2007. The second phase of construction, including the second bunch compressor and the FEL undulator, will begin later, in the Fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, energy spectrometers, S-band and X-band RF systems, the first bunch compressor stage, and the various beam diagnostics.

• W. E. White
  
• J. Castro, P. Emma, A. Gilevich, C. Limborg-Deprey, H. Loos, A. Miahnahri
  SLAC, Menlo Park, California

• A. S. Hofler
  
• P. Evtushenko
  Jefferson Lab, Newport News, Virginia
• M. Krasilnikov
  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.

• E. Pozdeyev
  

DC photoguns are used to produce high-quality, high-intensity electron beams for accelerator driven applications. Ion bombardment is credited as the major cause of degradation of the photocathode efficiency. Additionally to ions produced in the accelerating cathode-anode gap, the electron beam can ionize the residual gas in the transport line. These ions are trapped transversely within the beam and can drift back to the accelerating gap and contribute to the bombardment rate of the cathode. This paper proposes a method to reduce the flow of ions produced in the beam transport line and drifting back to the cathode-anode gap by introducing a positive potential barrier that repels the trapped ions. The reduced ion bombardment rate and increased life time of photocathodes will reduce the downtime required to service photoinjectors and associated costs.

• J. Smedley
  
• J. Iversen, D. Klinke, D. Kostin, W.-D. Moller, A. Muhs, J. S. Sekutowicz
  DESY, Hamburg
• P. Kneisel
  Jefferson Lab, Newport News, Virginia
• R. S. Lefferts, A. R. Lipski
  SBUNSL, Stony Brook, New York
• T. Rao
  BNL, Upton, Long Island, New York

We report recent progress in the development of a hybrid lead/niobium superconducting (SC) injector. The goal of this effort is to produce an all-SC injector with the SCRF properties of a niobium cavity along with the superior quantum efficiency (QE) of a lead photocathode. Two prototype hybrid injectors have been constructed, one utilizing a cavity with a removable cathode plug, and a second consisting of an all-niobium cavity arc-deposited with lead in the cathode region. We present the results of QE measurements on these cavities, along with tests of the effect of the laser on the cavity RF performance.

• V. Vogel
  
• A. Cherepenko
  BINP SB RAS, Novosibirsk
• S. Choroba, T. Froelich, T. G. Grevsmuehl, F.-R. Kaiser, V. V. Katalev, I. S. Sokolov, H. Timm
  DESY, Hamburg

• Y. H. Chin
  
• K. Hayashi
  TETD, Otawara
• M. Y. Miyake, Y. Yano
  Toshiba, Yokohama

• B. H. Chung
  
• K.-H. Chung
  KAPRA, Cheorwon
• J. S. Hong, J. H. Jeon, S. J. Noh
  Dankook University, Seoul
• S. K. Ko
  University of Ulsan, Ulsan

• M. J. Barnes
  
• T. Fowler, G. Ravida
  CERN, Geneva
• A. Ueda
  KEK, Ibaraki

• M. A. Kempkes
  
• M. P.J. Gaudreau, I. Roth, R. P. Torti
  Diversified Technologies, Inc., Bedford, Massachusetts

• H. Padamsee
  
• B. Ashmanskas
  Fermilab, Batavia, Illinois
• M. D. Cole, A. J. Favale, J. Rathke
  AES, Princeton, New Jersey
• A. C. Crawford
  CLASSE, Ithaca

We have recently upgraded our chemical treatment, high pressure rinsing systems and low temperature RF testing system to prepare and test 9-cell cavities for ILC. After removal of 120 um by BCP we reached 26 MV/m accelerating field limited by the high-field Q-slope. There was no quench and no field emission, showing that our facilities are well qualified. We have also extended our vertical electropolishing system to 9-cell cavities. Previously we have successfully used vertical electropolishing for one-cell cavities of the re-entrant shape to reach 47 MV/m accelerating. Test results on 9-cell electropolished cavities will be presented. AES has manufactured the first 9-cell cavity with re-entrant cell shapes. The surface magnetic field is 10% lower than for the standard TESLA-shape cavity. Half-cells were electropolished 100 um before welding. We will present results on the first tests of the 9-cell re-entrant cavity.

• A. V. Morgan
  
• H. Padamsee
  Cornell University, Ithaca, New York
• A. Romanenko, A. J. Windsor
  CLASSE, Ithaca

Electropolishing is now the preferred method for chemical treatment of niobium cavity surfaces. It provides a very smooth surface and after baking accelerating fields between 35 - 40 MV/m. However the reproducibility of performance needs to be improved substantially. Some of the leading causes are related to contaminant residues after electropolishing, these include sulphur particles, niobium pentoxide particles and traces of aluminum from reaction between the aluminum cathode and the acid electrolyte. We have carried out studies to enhance the deposition of such particles so that we can isolate and study the residues. We will present analysis of these studies using optical microscopy, SEM, and Auger. In at attempt to dissolve these contaminants, we have also conducted studies on the effectiveness of various rinsing agents, such as degreasing agents, dilute HF, hydrogen peroxide.

• K. Nielsen
  
• J. Barraza, M. Kang
  LANL, Los Alamos, New Mexico
• F. M. Bieniosek, K. Chow, W. M. Fawley, E. Henestroza, L. R. Reginato, W. L. Waldron
  LBNL, Berkeley, California
• R. J. Briggs, B. A. Prichard
  SAIC, Alamo, California
• T. E. Genoni, T. P. Hughes
  Voss Scientific, Albuquerque, New Mexico

• W. Reass
  
• V. P. Derenchuk, T. Rinckel, G. Visser
  IUCF, Bloomington, Indiana
• D. Rees
  LANL, Los Alamos, New Mexico

This paper describes the Klystron RF systems for the Indiana University Low Energy Neutron Source (LENS) accelerator 425 MHz Radio Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) systems. Of interest in the power conditioning system is the design of the totem-pole grid-catch modulator for the mod-anode klystrons. This topology provides a fast rise and fall and closed loop regulation for the klystron mod-anode to cathode voltage, which minimizes RF amplitude and phase droop while maximizing efficiency. Another advantage is that short pulse high rep-rate operation is viable within the average power capabilities of the klystron. The 425 MHz, 1.25 MW klystron amplifier chain will also be detailed. Of final interest, is the digital low level RF system. This provides vector control of the cavity field using direct conversion, non-I/Q sampling architecture, at a sampling rate of 132 MHz with a 12-bit ADC. Four input and two output channels are integrated into a 6U VME module, with all DSP functions performed in Xilinx Spartan-3 field-programmable gate arrays. The design and implementation of these systems, coupled with LENS operational results, will be presented.

• K. A. Young
  
• G. O. Bolme, J. T.M. Lyles, M. T. Lynch, E. P. Partridge, D. Rees
  LANL, Los Alamos, New Mexico

The LANSCE RF system consists of four RF stations at 201 MHz and 44 klystrons at 805 MHz. In the LANSCE accelerator, the beam source is injected into the RF system at 0.75 MeV. The beam is then accelerated to 100 MeV in four drift tube linac (DTL) tanks, driven at 201.25 MHz. Each 201 MHz RF system consists of a train of amplifiers, including a solid state amplifier, a tetrode, and then at triode. After the DTL, the beam is accelerated from 100 MeV to 800 MeV in the forty-four coupled cavity linac (CCL) tanks at 805 MHz. The machine operates with a normal RF pulse width of 835 microseconds at a repetition rate up to 120 Hz, and sometimes operates with a pulse width up to 1.2 microseconds for single pulses. This RF system has been operating for about 37 years. This paper summarizes the recent operational experience. The reliability of the 805 MHz and 201 MHz RF systems is discussed, and a summary the lifetime data of the 805 MHz klystrons and 201 MHz triodes is presented.

• A. M. Cook
  
• M. P. Dunning, J. B. Rosenzweig, K. M. Serratto
  UCLA, Los Angeles, California
• P. Frigola
  RadiaBeam, Los Angeles, California

The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, the full cell geometry must be changed significantly. We report on a method of accomplishing this, in which we use a mechanical device of custom design to stretch the cavity structure of an existing photoinjector in order to tune the resonant frequency up by over 2 MHz. We present results of testing the modified photoinjector in an RF test bed with both copper and magnesium cathodes, succeeding in putting approximately 8 - 10 MW of RF power into the gun. This is an improvement over the 4 MW routinely achieved in a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory.

• B. D. O'Shea
  
• D. Alesini, M. Ferrario, B. Spataro
  INFN/LNF, Frascati (Roma)
• A. Boni, A. Fukasawa, J. B. Rosenzweig
  UCLA, Los Angeles, California
• L. Ficcadenti, A. Mostacci, L. Palumbo
  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.

• J. J. Mize, J. J. Mize
  ORNL, Oak Ridge, Tennessee

The high frequency switching megawatt-class High Voltage Converter Modulator (HVCM) developed by Los Alamos National Laboratory for the Oak Ridge National Laboratory's Spallation Neutron Source (SNS), is now in operation. One of the major problems with the modulator systems is shoot-thru conditions that can occur in an IGBTs H-bridge topology resulting in large fault currents and device failure in a few microseconds. The Dynamic Fault Detection Chassis (DFDC) is a fault monitoring system; it monitors transformer flux saturation using a window comparator and dV/dt events on the cathode voltage caused by any abnormality such as capacitor breakdown, transformer primary turns shorts, or dielectric breakdown between the transformer primary and secondary. If faults are detected, the DFDC will inhibit the IGBT gate drives and shut the system down, significantly reducing the possibility of a shoot-thru condition or other equipment damaging events. In this paper,we will present system integration considerations, performance characteristics of the DFDC, and discuss its ability to significantly reduce costly down time for the entire facility.

• N. Barov
  

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.

• A. Burrill
  
• I. Ben-Zvi
  BNL, Upton, Long Island, New York
• M. D. Cole, J. Rathke
  AES, Princeton, New Jersey
• P. Kneisel, R. Manus, R. A. Rimmer
  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.

• X. Chang
  
• I. Ben-Zvi, J. Kewisch, C. Pai
  BNL, Upton, Long Island, New York

• C. Wilsen
  
• M. F. Kirshner, R. D. Kowalczyk
  L-3, Williamsport, Pennsylvania

* M. F. Kirshner et al., "Apparatus and method for trajectory modulation of an electron beam," U. S. Provisional Patent Application 60/838,580, August 17, 2006. Cleared by DoD/OFOISR for public release under 07-S-0493 on January 22, 2007

• A. Balkcum
  
• T. W. Habermann
  CPI, Palo Alto, California

* A. Balkcum, et al. "Operation of a 1.3 GHz Multiple Beam Klystron," Proc. of 6th IVEC, pp. 505, Noordwijk (2005).

• M. N. Martins
  
• A. L. Bonini, R. Lima, A. A. Malafronte, T. F. Silva
  USP/LAL, Sao Paulo

The injector linac consists of a beam conforming stage, with chopper and buncher systems, and two acceleration structures, the first one with variable β, and the second one divided into two parts with different β. There are two 3-mm diameter collimators, the first at the entrance to the first chopper cavity and the second at the entrance to the first acceleration structure. The beam focalization is made by solenoids, and correcting coils are provided for steering. In this work we describe the commissioning of the optical lattice of the conforming beam stage. The first beam images are shown.

• P. Musumeci
  
• J. Moody
  UCLA, Los Angeles, California

• D. Sertore
  
• P. Michelato, L. Monaco, C. Pagani
  INFN/LASA, Segrate (MI)

Based on our experience on photocathode production, we present in this paper the results of the application of different optical diagnostic techniques on fresh and used photocathodes. These techniques allow to study effects like non uniformity, cathode aging, etc. In particular, photocathode optical parameters and QE characterization, both done at different wavelengths, give fundamentals information for the construction of a model of the photoemission process to be applied to Cs2Te photocathodes. These studies are useful for further improving key cathode features, such as its robustness and lifetime as well as to study and control the photocathodes thermal emittance.

• L. Monaco
  
• J. W. Baehr, M. Krasilnikov, S. Lederer, F. Stephan
  DESY Zeuthen, Zeuthen
• J. H. Han, S. Schreiber
  DESY, Hamburg
• P. Michelato, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)

The FLASH (DESY-Hamburg) and PITZ (DESY-Zeuthen) photoinjectors routinely use high quantum efficiency (QE) photocathodes produced at LASA (INFN-Milano), since 1998. To further understand the photocathode behavior during beam operation, photocathode QE measurements have been performed at different operating conditions in both RF photoinjectors. The analysis of these measurements will be used to improve the photocathode preparation procedures and to deeper understand the photocathode properties, whose final goal would be the further increase of their lifetime and beam quality preservation during the RF gun operations.

• T. Sugimura
  
• M. Ikeda, S. Ohsawa
  KEK, Ibaraki

• F. Sakamoto
  
• M. Akemoto, T. Higo, J. Urakawa
  KEK, Ibaraki
• D. Ishida, N. Kaneko, H. Nose, H. Sakae, Y. Sakai
  IHI/Yokohama, Kanagawa
• T. Natsui, Y. Taniguchi, M. Uesaka, T. Yamamoto
  UTNL, Ibaraki
• M. Yamamoto
  Akita National College of Technology, Akita

• A. Sakumi
  
• Y. Muroya, T. Ueda, M. Uesaka
  The University of Tokyo, Nuclear Professional School, Ibaraki-ken

• A. Yamazaki
  
• T. Hosokai, K. Kinoshita, A. Maekawa, R. Tsujii, M. Uesaka, A. G. Zhidkov
  UTNL, Ibaraki

• T. Kondoh
  
• H. Kashima, J. Yang, Y. Yoshida
  ISIR, Osaka

• Y. Kamiya
  
• Y. Kato, A. Murata, K. Sakaue, M. Washio
  RISE, Tokyo
• N. Kudoh, M. Kuriki, T. T. Takatomi, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• R. Kuroda
  AIST, Tsukuba, Ibaraki

• G. Feng
  
• Y. Hong, Y. J. Pei, X. Wang
  USTC/NSRL, Hefei, Anhui

• S. P. Antipov
  
• M. E. Conde, W. Gai, J. G. Power, Z. M. Yusof
  ANL, Argonne, Illinois
• V. A. Dolgashev
  SLAC, Menlo Park, California
• L. K. Spentzouris
  Illinois Institute of Technology, Chicago, Illinois

A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator Facility (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. An imaging system is being put together to identify single emitters on the cathode surface. This will allow us to study dark current properties in the gun. We also plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV). Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after can shed some light on a modification of metal surface after the breakdown.

• J. W. Staples
  
• K. M. Baptiste, J. N. Corlett, S. Kwiatkowski, S. M. Lidia, J. Qiang, F. Sannibale, K. G. Sonnad, S. P. Virostek, R. P. Wells
  LBNL, Berkeley, California

New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photoinjectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100 MHz CW, to provide beam bunches at a rate of one MegaHertz or more. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm². The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for flat beam generation. Beam dynamics simulations indicate that normalized emittances on the order of 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10's of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.

• T. Bemis
  
• R. Bhatt, C. Chen, J. Z. Zhou
  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.

• N. Vinogradov
  
• C. L. Bohn, P. Piot
  Northern Illinois University, DeKalb, Illinois
• J. W. Lewellen, J. Noonan
  ANL, Argonne, Illinois

• T. L. Houck
  
• C. G. Brown, D. E. Fleming, B. R. Kreitzer, K. E. Lewis, M. M. Ong, J. M. Zentler
  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.

• J. E. Spencer
  
• R. J. Noble
  SLAC, Menlo Park, California

Luminosity considerations for microscale accelerators intended for high-energy physics place a high premium on the bunch repetition rate and phase space density at the interaction point. The NLC Test Accelerator (NLCTA) at SLAC was built to address such beam dynamics issues for the Next Linear Collider and beyond. Because an S-Band RF gun has been installed together with a low-energy, high-resolving power spectrometer (LES), it is useful to explore alternatives to conventional scenarios with it. We consider possibilities that can be tested with minimal modification to this system e.g. cases that involve producing multiple bunches from the cathode in different formats such as a 2D planar matrix or 3D tensor beam made of smaller bunches or bunchlets that replace the usual, single higher charge bunches. Thus, we study configurations of interacting bunchlets n_ij or n_ijk coming from the cathode and passing through the emittance compensating solenoids that can be matched to the linac or focussed on the LES focal plane at 6 MeV. Parmela calculations have been done that show no significant space charge effects or emittance increases for pC bunchlet charges.

• H. Bluem
  

High power RF testing has been performed on a novel axisymmetric radiofrequency electron gun at a frequency of 11.43 GHz using the magnicon facility at the Naval Research Laboratory. This gun utilizes coaxial coupling from the upstream end of unit and allows for axisymmetric tuning of both the cathode cell and the second cell. The features of the gun have been proven to operate at high gradients. The overall design of the gun will be discussed along with the results of the high power RF testing.

• R. B. Yoder
  
• J. B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California

*R. Yoder and J. Rosenzweig, Phys. Rev. STAB 8, 111301 (2005); Z. Zhang et al., Phys. Rev. STAB 8, 071302 (2005); A. Mizrahi and L. Schachter, Phys. Rev. E 70, 016505 (2004).

• J. Kewisch
  
• X. Chang
  BNL, Upton, Long Island, New York

An electron cooler, based on an Energy Recovery Linac (ERL) is under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. In order to achieve sufficient cooling of the ion beams the electron have to have a charge of 5 nC and a normalized emittance less than 4 mm mrad. This paper presents the progress in optimizing the injector and the emittance improvements from shaping the charge distribution in the bunch.

• J. Kewisch
  
• X. Chang
  BNL, Upton, Long Island, New York

Emittance compensation is a well established technique* for minimizing the emittance of electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincides the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in reference**. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating frame. We describe a method and tools for a compensation that includes the beam magnetization.

* L. Serafini, J. B. Rosenzweig, Phys. Rev E 55, 7565, (1997)
** X. Y. Chang, I. Ben-Zvi, J. Kewisch, Phys. Rev ST AB 9, 044201, (2006)

• S. H. Gold
  
• W. Gai, R. Konecny, J. Long, J. G. Power
  ANL, Argonne, Illinois
• C.-J. Jing
  Euclid TechLabs, LLC, Solon, Ohio
• A. K. Kinkead
  LET
• C. D. Nantista, S. G. Tantawi
  SLAC, Menlo Park, California

A joint project is underway by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a compact X-band accelerator for testing dielectric-loaded accelerator (DLA) structures.* The accelerator will use a 5-MeV injector previously developed by the Tsinghua University in Beijing, China, and will accommodate test structures up to 0.5 m in length. Both the injector and the structures will be powered by an 11.4-GHz magnicon amplifier that can produce 25 MW, 200-ns output pulses at up to 10 Hz. The injector will require ~5 MW of rf power, leaving ~20 MW to power the test structures. This paper will present a progress report on the construction and commissioning of the test accelerator, which will be located in a concrete bunker in the Magnicon Facility at NRL.

* S. H. Gold et al., Proc. PAC 2005.

• O. Mouton
  
• M. Caron, F. Cartier, D. Collignon, G. Grandpierre, D. Guilhem, L. Hourdin, M. Mouillet, C. Noel, D. Paradis, O. Pierret
  CEA, Pontfaverger-Moronvilliers

• S. Schnepp
  
• E. Gjonaj, T. Weiland
  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.

• G. M. Wang, G. M. Wang
  JLAB, Newport News, Virginia
• Y.-C. Chao, P. Evtushenko, G. Neil
  Jefferson Lab, Newport News, Virginia
• J.-E. Chen, C. Liu, X. Y. Lu, K. Zhao
  PKU/IHIP, Beijing

We present work directed at examining the performance of various front end components of an ERL based light source. These include electron source, bunch compression, merger, and accelerating sections, with parameter space dictated by proposed facilities (at FSU and Beijing University). These facilities share enough common structural features to make the study applicable to both to a large extent. In this report we will discuss the 6D phase space evolution through the front end based on simulation, with reliable modeling of magnetic and superconducting RF fields. Discussion will be devoted to relative merits of alternative designs, robustness and operational scenarios.

• M. Hess
  
• C. S. Park
  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).

• C. S. Park
  
• M. Hess
  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.

• I. Haber
  
• S. Bernal, R. Feldman, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, D. Stratakis, M. Walter
  UMD, College Park, Maryland
• A. Friedman, D. P. Grote
  LLNL, Livermore, California
• J.-L. Vay
  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.

• J. C.T. Thangaraj
  
• G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, K. Tian, M. Walter
  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.

• J. F. DeFord
  
• B. Held
  STAR, Inc., Mequon, Wisconsin
• J. J. Petillo
  SAIC, Burlington, Massachusetts

Particle orbit errors in multipacting and dark current computations can arise from inadequate field representation, poor surface modeling, and from the integration algorithm used to advance the particles. Established fields-based adaptive mesh refinement (AMR) methods *,** selectively improve the field and surface representation over several iterations in finite-element codes but they are not optimized for particle tracking. In particular, field emission and secondary emission models require precise surface representations and highly accurate field representations near surfaces, and these requirements are not adequately addressed in standard AMR techniques. In this paper we report on extensions to existing AMR support in the Analyst software package for particle tracking, including adaptive improvement of near-surface and on-surface field representations, and control of element aspect ratios throughout successive iterations. We also discuss the merits of automated identification of important regions of the mesh based on field levels and orbit estimation to guide AMR in multipacting calculations, and multipacting results for a SRF cavity will be presented.

* G. Drago, et al., IEEE Trans. on Mag., 28, 1992, pp. 1743-1746.** D. K. Sun, et al., IEEE Trans. on Mag., 36, July 2000, pp. 1596-1599.

• A. Fukasawa
  
• D. Alesini, M. Ferrario, B. Spataro
  INFN/LNF, Frascati (Roma)
• A. Boni, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California
• L. Ficcadenti, A. Mostacci, L. Palumbo
  Rome University La Sapienza, Roma

• A. Krasnykh
  

A novel 3D method of sheet beam (SB) gun design has recently been developed. Second order ruled surfaces (SORS) to define the geometry of the gun electrodes. The gun design process is made simpler if SORS are derived from simple analytical formulas. The coefficients of the mathematical expression are parameters that set the gun optic. A proposed design method is discussed and illustrated.

• M. S. Champion
  

• T. F. Silva
  
• A. A. Malafronte, M. N. Martins
  USP/LAL, Sao Paulo

In this work we describe the determination of the beam emittance for the 100-keV injector of the IFUSP racetrack microtron. We measured the beam spot diameter at a fluorescent screen located 40 cm after a 3-mm diameter collimator (placed at the entrance to the first chopper cavity). A solenoid lens located upstream to the collimator was used to produce a beam waist at the fluorescent screen position. We used the collimator and the beam waist sizes to calculate the emittance for 80 and 90 keV beams. Results showed no dependence with energy, indicating that the collimator is limiting the beam emittance at 2.32(5) ??mm?mrad.

• R. Tsujii
  
• T. Hosokai
  RLNR, Tokyo
• K. Kinoshita, Y. Kondo, A. Maekawa, Y. Shibata, M. Uesaka, A. Yamazaki
  UTNL, Ibaraki
• T. Takahashi
  KURRI, Osaka
• A. G. Zhidkov
  Central Research Institute of Electric Power Industry, Komae

• V. Volkov
  
• K. Floettmann
  DESY, Hamburg
• D. Janssen
  FZD, Dresden

• G. Huang
  
• J. M. Byrd, J. Feng, J. Qiang, W. Wan
  LBNL, Berkeley, California

• J. Qiang
  
• J. M. Byrd, J. Feng, G. Huang
  LBNL, Berkeley, California

Streak camera is an important diagnostic device in the studies of laser plasma interaction, the detailed structure of photo reaction from material science to biochemistry, and in the measurement of the longitudinal distribution of a beam in accelerators. In this paper, we report on a new method which can potentially improve the temporal resolution of a streak camera down to femtoseconds. This method uses a time-dependent acceleration field to defocus the photo electrons longitudinally. This not only reduces the time dispersion distortion caused by initial energy spread but also mitigates the effects from the space-charge forces. An illustration of the method shows significant improvement of the modulation transfer function (MFT) compared with the conventional design.