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plasma

     
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MO202 High-Intensity, High Charge-State Heavy Ion Sources ion, electron, laser, ion-source 8
 
  • J. Alessi
    BNL, Upton, Long Island, New York
  There are many accelerator applications for high intensity heavy ion sources, with recent needs including dc beams for RIA, and pulsed beams for injection into synchrotrons such as RHIC and LHC. The present status of sources producing high currents of high charge state heavy ions will be reviewed. These sources include ECR, EBIS, and Laser ion sources. The benefits and limitations for these type sources will be described, for both dc and pulsed applications. Possible future improvements in these type sources will also be discussed.  
Transparencies
 
MOP72 RF Breakdown in Accelerator Structures: From Plasma Spots to Surface Melting electron, site, simulation, radio-frequency 189
 
  • P.B. Wilson
    SLAC, Menlo Park, California
  Plasma spots are known to form at field emission sites in regions of high dc or rf electric field. Several mechanisms for the formation of plasma spots in an rf field have been proposed, and one such mechanism which fits experimental data is presented in this paper. However, a plasma spot by itself does not produce breakdown. A single plasma spot, with a lifetime on the order of 30 ns, extracts only a negligible amount of energy from the rf field. The evidence for its existence is a small crater, on the order of 10 microns in diameter, left behind on the surface. In this paper we present a model in which plasma spots act as a trigger to produce surface melting on a macroscopic scale (~0.1 mm2). Once surface melting occurs, a plasma that is capable of emitting several kiloamperes of electrons can form over the molten region. A key observation that must be explained by any theory of breakdown is that the probability of breakdown is independent of time within the rf pulse–breakdown is just as likely to occur at the beginning of the pulse as toward the end. In the model presented here, the conditions for breakdown develop over many pulses until a critical threshold for breakdown is reached.  
Transparencies
 
MOP73 Development of a Permanent Magnet ECR Source to Produce a 5 mA Deuteron Beam at CEA/Saclay extraction, emittance, simulation, permanent-magnet 192
 
  • R. Gobin, D.D. De Menezes, O. Delferriere, R. Ferdinand, F. Harrault
    CEA/DAPNIA-SACM, Gif-sur-Yvette Cedex
  • P.-Y. Beauvais, G. Charruau, Y. Gauthier
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  • N. Comte
    CEA/Saclay, Gif-sur-Yvette
  • P. Lehérissier, J.Y. Pacquet
    GANIL, Caen
  The high intensity light ion source, SILHI, is an ECR ion source operating at 2.45 GHz which produces high intensity (over 100 mA) proton or deuteron beams at 95 keV. It has been moved in the IPHI building after a complete dismantling. At the beginning of 2003, after tuning the source parameters at standard values, the first extracted beam reached more than 70 mA within a few minutes. This encouraged us to propose a permanent magnet source based on the SILHI design to fit in with the injector of the Spiral2 project, requesting 5 mA of D+ beam with an energy of 40 keV and a normalized rms emittance lower than 0.2 π·mm·mrad. The new source has been recently assembled and the first beam (proton) extracted. After a brief source description, the preliminary results will be reported and discussed.  
 
MOP74 Recent Results of the 2.45 GHz ECR Source Producing H- Ions at CEA/Saclay ion, electron, ion-source, extraction 195
 
  • R. Gobin, K. Benmeziane, O. Delferriere, R. Ferdinand, F. Harrault
    CEA/DAPNIA-SACM, Gif-sur-Yvette Cedex
  • A. Girard
    CEA DSM Grenoble, Grenoble
  Low frequency ECR plasma sources have demonstrated their efficiency, reproducibility and long life time for the production of positive light ions. In 2003, the new 2.45 GHz ECR test stand based on a pure volume H- ion production, developed at CEA/Saclay, showed a dramatic increase of the H- extracted ion beam. In fact, a stainless steel grid now divides the plasma chamber in two different parts: the plasma generator zone and the negative ion production zone. By optimizing the grid position and its potential with respect to the plasma chamber, the negative ion current reached close to 1 mA. Ceramic plates, covering the plasma chamber walls help electron density and lead to an optimisation of the ion production. A 50 % improvement has been observed. A new 6 kW magnetron RF generator now replaces the 1.2 kW previous one and the current will be soon plotted versus the RF power. New Langmuir probe measurements are also expected on both sides of the grid. The last results will be reported and discussed.  
Transparencies
 
MOP75 Hminus Distribution in the HERA RF-Volume Source laser, electron, acceleration, extraction 198
 
  • J. Peters
    DESY, Hamburg
  The HERA RF-Volume Source is the only source available that delivers routinely an Hminus current of 40 mA without Cs. The production mechanism for Hminus ions in this type of source is still under discussion. Laser photodetachment measurements have been started at DESY in order to measure the Hminus distribution in the source. The measurements have also been done under extraction conditions at high voltage. The results of the measurements with and without extraction are a basis for the development of a theory for the transition between plasma and vacuum (sheath), a cornerstone for beam transport programs. Knowledge of the H- distribution and where they are produced makes further source improvements possible.  
 
TU102 Survey of Advanced Acceleration Techniques electron, laser, acceleration, undulator 242
 
  • C.J. Joshi
    UCLA, Los Angeles, California
  In this talk I will review the recent progress on the production, manipulation, transport, acceleration and focusing of relativistic electron beams using advanced techniques. In particular, I will report recent progress on cathode-less electron injectors, IFEL bunchers and accelerators, plasma accelerating and transport structures, and electron and positron beam focusing using plasmas. The plasma structures for acceleration can be excited either by laser beams or charged-particle beams. The acceleration gradients in either case can be enormous. For unmatched beams the betatron radiation loss, as the beam oscillates transversely in the high gradient accelerating structure, can generate a high brightness x-ray beam. These x-rays can, in turn, be used to generate positrons. Work done by different groups around the world will be reviewed.  
Transparencies
 
TUP11 High current RFQ using laser ion source rfq, laser, ion, ion-source 315
 
  • M. Okamura, R.A. Jameson, J. Takano, K. Yamamoto
    RIKEN, Saitama
  • R. Becker, A. Schempp
    IAP, Frankfurt-am-Main
  • T. Fujimoto
    AEC, Chiba
  • T. Hattori, N. Hayashizaki
    TIT, Tokyo
  • Y. Iwata, S. Shibuya
    NIRS, Chiba-shi
  • H. Kashiwagi
    JAERI/ARTC, Gunma-ken
  A new RFQ was fabricated for very high current heavy ions. The designed target current is 100 mA with cabon 4+ beam. Acceleration test result will be reported at the conference.  
 
TUP84 Spectrographic Approach to Study of RF Conditioning Process in Accelerating RF Structures RF-structure, vacuum, quadrupole, electron 471
 
  • H. Tomizawa, H. Hanaki, T.  Taniuchi
    JASRI-SPring-8, Hyogo
  • A. Enomoto, Y. Igarashi, S. Yamaguchi
    KEK, Ibaraki
  The acceleration gradient of a linac is limited by rf breakdown in its accelerating structure. We applied an imaging spectrograph system to study the mechanism of rf breakdown phenomena in accelerating rf structures. Excited outgases emit light during rf breakdown, and the type of outgases depend on surface treatments and rinsing methods for their materials. To study rf breakdown, we used 2-m-long accelerating structures and investigated the effects when high-pressure ultrapure water rinsing (HPR) treatment was applied to these rf structures. We performed experiments to study the outgases under rf conditioning with quadruple mass spectroscopy and imaging spectrography. As a result, we could observe instantly increasing signals at mass numbers of 2 (H2), 28 (CO), and 44 (CO2), but not 18 (H2O) just after the rf breakdown. We also conducted spectral imaging for the light emissions from the atoms in a vacuum that are excited by rf breakdown. Without HPR, we observed the atomic lines at 511 nm (Cu I), 622 nm (Cu II), and 711 nm (C I). With HPR, 395 nm (O I), 459 nm (O II), 511 nm (Cu I), 538 nm (C I), 570 nm (Cu I), 578 nm (Cu I), 656 nm (H I), and 740 nm (Cu II) were observed.  
 
WE101 Gradient Limitations for High-Frequency Accelerators collider, linear-collider, linac, vacuum 513
 
  • S. Döbert
    SLAC, Stanford
  While the physics of gradient limitations in high frequency rf accelerators still lacks a full theoretical understanding, a fairly complete empirical picture has emerged from the experimental work done in the past few years to characterize this phenomenon.Experimental results obtained mostly in the framework of the NLC/GLC project at 11 GHz and from the CLIC study at 30 GHz will be used to illustrate the important trends.The dependence of achievable gradient on pulse length, operating frequency and fabrication materials will be described. Also, the performance results most relevant to linear colliders will be presented in some detail. Specifically, these relate to the requirements that the structures sustain a certain gradient without incurring damaged, and that more importantly, they run reliably at this gradient, with breakdown rates less one in a million pulses. Finally interesting observations concerning the dynamics of breakdowns like spatial and temporal correlations and dark currents will be covered briefly, including the insights they provide into the breakdown mechanism.  
Transparencies
 
THP74 Laser Produced Ions as an Injection Beam for Cancer Therapy Facility laser, ion, target, proton 782
 
  • A. Noda, M. Hashida, Y. Iwashita, S. Nakamura, S. Sakabe, S. Shimizu, T. Shirai, H. Tongu
    Kyoto ICR, Kyoto
  • H. Daido
    JAERI APRC, Ibaraki-ken
  • A. Fukumi, Z. Li, K. Matsukado
    NIRS, Chiba-shi
  • T. Hosokai, H. Iijima, K. Kinoshita, M. Uesaka, T. Watanabe, K. Yoshii
    UTNL, Ibaraki
  • T. Takeuchi
    DOP Nagoya, Nagoya
  Ion production from a solid target by a high-power short pulse laser has been investigated to replace the injector linac of the synchrotron dedicated for cancer therapy. As the high power laser, the laser with the peak power of 100 TW and minimum pulse duration of 20 fs which has been developed at JAERI Kansai Research Establishment, is assumed. Laser produced ions with 100% energy spread is energy selected within ±5% and then phase rotated with use of the RF electric field synchronized to the pulse laser, which further reduces the energy spread to ±1%. The scheme of the phase rotation is presented together with the experimental results of laser production from the thin foil target.  
 
THP84 Design of a 300 GHz Broadband TWT Coupler and RF-Structure coupling, simulation, RF-structure, electron 794
 
  • F.L. Krawczyk, F.E. Sigler
    LANL/LANSCE, Los Alamos, New Mexico
  • B.E. Carlsten, L.M. Earley
    LANL, Los Alamos, New Mexico
  • J.M. Potter
    JP Accelerator Works, Inc., 2245, Los Alamos, NM
  • M.E. Schulze
    GA, Los Alamos
  • E. Smirnova
    MIT/PSFC, Cambridge, Massachusetts
  Recent LANL activities in millimeter wave structures focus on 94 and 300 GHz structures. They aim at power generation from low power (100–2000 W) with a round electron beam (120 kV, 0.1–1.0 A) to high power (2–100 kW) with a sheet beam structure (120 kV, 20 A). Applications cover basic research, radar and secure communications and remote sensing of biological and chemical agents. In this presentation the design and cold-test measurements of a 300 GHz RF-structure with a broadband (>6% bandwidth) power coupler are presented. The design choice of two input/output waveguides, a special coupling region and the structure parameters themselves are presented. As a benchmark also a scaled up version at 10 GHz was designed and measured. These results will also be presented.  
 
THP93 A 3D Self-Consistent, Analytical Model for Longitudinal Plasma Oscillation in a Relativistic Electron Beam electron, space-charge, simulation, linac 818
 
  • G. Geloni, E. Saldin, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg
  Longitudinal plasma oscillations are becoming a subject of great interest for XFEL physics in connection with LSC microbunching instability[1] and certain pump-probe synchronization schemes[2]. In the present paper we developed the first exact analytical treatment for longitudinal oscillations within an axis-symmetric, (relativistic) electron beam, which can be used as a primary standard for benchmarking space-charge simulation codes. Also, this result is per se of obvious theoretical relevance as it constitutes one of the few exact solutions for the evolution of charged particles under the action of self-interactions.

[1] E. Saldin et al., "Longitudinal Space Charge Driven Microbunching instability in TTF linac", TESLA-FEL-2003-02, May 2003, [2] J. Feldhaus et al., "Two-color FEL amplifier for femtosecond-resolution pump-probe experiments with GW-scale X-ray and optical pulses",DESY 03-091, July 2003