TPPE  —  Sources and Injectors   (17-May-05   13:50—17:10)

Paper Title Page
TPPE001 The HERA Volume H- Source 788
 
  • J. Peters
    DESY, Hamburg
 
  Funding: The support of EEC (Contract HPRI-CT-2001-50021) is gratefully acknowledged.

The HERA RF-Volume Source is the only source that delivers routinely a H – current of 40 mA without Cs. It has been running for years without interruption for maintenance. The production mechanism for H – ions in this type of source is still under discussion. Laser photodetachment measurements have been done at DESY in order to measure the H – distribution in the source. The measurements were done also under extraction conditions at high voltage. The dependency of the quality of the Hminus beam on the frequency was investigated. A frequency range of 1.65 – 9 Mhz was scanned and the emittance was measured for several Hminus currents up to 40 mA. The results of our investigations make further source improvements possible. Recently currents of 60 mA were reached.

 
TPPE003 Analysis of Multigrid Extraction Plasma Meniscus Formation 862
 
  • M. Cavenago
    INFN/LNL, Legnaro, Padova
  • V. Antoni, F. Sattin
    CNR/RFX, Padova
  • A. Tanga
    MPI/IPP, Garching
 
  Funding: INFN-LNL, CNR-RFX.

Effects of plasma meniscus on the emittance in negative ion source proposed for spallation sources or neutral beam injectors (NBI) for tokamaks are particularly interesting to study with fluid models because: 1) at least three different charged fluid can be recognised: the thermalized and fully magnetized electrons; the slightly magnetized and roughly thermalized positive ions; the negative ions, typically formed within few cm from meniscus; 2) different implementation of the magnetic filter system need to be compared; 3) optimization of electron dump and outlet electrode strongly depends on plasma meniscus contact point. With reasonable assumption on system geometry, 2D and 3D charged fluid quation for the selfconsistent electrostatic field can be written and effect of grid aperture is investigated. Moreover, these equations are easily implemented into a multiphysics general purpose program. Preliminary results are described, and compared to existing codes.

 
TPPE004 The Production of Negative Lithium Beams by Charge Exchange in Cesium Vapours 898
 
  • M. Re, F. Chines, G. Cuttone, M. Menna, E. Messina
    INFN/LNS, Catania
  • J.-C. Bilheux, D.W. Stracener
    ORNL, Oak Ridge, Tennessee
 
  These measurements were carried out at the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory (ORNL-HRIBF) by researchers from the Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud (INFN-LNS), Catania, Italy and local staff. The Charge Exchange Cell (CEC) consisted of a vacuum chamber containing cesium vapours at a variable temperature, T, in which positive ions accelerated from an ion source were transformed into negative ones by collisions with the Cs atoms. The main goal of this test was to measure the production efficiency for 7Li- ions at different operating conditions, such as 7Li+ beam energy (5 to 55 keV) and Cs temperature (190 to 300 °C). Moreover, the efficiency measurements performed with a 6Li+ projectile beam gave clear indications about the isotopic shift effect. These results are useful to estimate the charge exchange efficiency for 8, 9Li, which will be the first radioactive beams to be produced at the EXCYT facility (EXotics with CYclotron and Tandem). The data showed that the charge exchange efficiency at the minimum energy suitable for beam handling (20-25 keV) is around 1%.  
TPPE005 50keV, 50mA Pulsed Proton Injector for PEFP 964
 
  • I.-S. Hong, Y.-S. Cho, S.-H. Han
    KAERI, Daejon
 
  Funding: This work is supported by the 21C Frontier R&D program in the Ministry of Science and Technology of the Korean government.

Duoplasmatron type ion source with 50keV proton beam has been constructed and stably operated as the injector for Proton Engineering Frontier Project(PEFP). In DC operation, the beam current of 50mA with 50kV extraction voltage is routinely obtained. However, the pulsed operation mode of the ion source also has been considered to reduce beam induced damage at the entrance of RFQ. A high voltage pulse switch is connected between accelerating electrode and ground electrode for this purpose. The detailed scheme on the focusing of the pulsed proton beam with space charge compensation is in progress. Beam profile and current in front of RFQ will be measured by DCCT and optical measuring tools.

 
TPPE006 Radioactive Beams from 252CF Fission Using a Gas Catcher and an ECR Charge Breeder at ATLAS 1000
 
  • R.C. Pardo, S.I. Baker, A.A.H. Hecht, E.F. Moore, G. Savard
    ANL, Argonne, Illinois
 
  Funding: Department of Energy Office of Nuclear Science.

An upgrade to the radioactive beam capability of the ATLAS facility has been proposed using 252Cf fission fragments thermalized and collected into a low-energy particle beam using a helium gas catcher. In order to reaccelerate these beams an existing ATLAS ECR ion source will be reconfigured as a charge breeder source. A 1Ci 252Cf source is expected to provide sufficient yield to deliver beams of up to ~106 far from stability ions per second on target. A facility description, the expected performance and the expected performance will be presented in this paper. This work is supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract W-31-109-ENG-38.

 
TPPE007 Energy Correction for High Power Proton/H Minus Linac Injectors 1075
 
  • D. Raparia, Y.Y. Lee, J. Wei
    BNL, Upton, Long Island, New York
 
  High-energy proton/H minus (> GeV) linear accelerators suffer from energy jitter due to RF amplitude and phase stability. For high-power operations, such energy jitter often results in beam losses at more than 1 W/m level required for hands-on maintenance. Depending upon the requirements for next accelerator in the chain, this energy jitter may or may not require correction. This paper discusses the sources of energy jitter and correction feasibility with specific examples of the Spallation Neutron Source linac and a higher-energy H minus linac.  
TPPE010 A Parallel 3D Model for the Multi-Species Low Energy Beam Transport System of the RIA Prototype ECR Ion Source VENUS 1183
 
  • J. Qiang, D. Leitner, D.S. Todd
    LBNL, Berkeley, California
 
  Funding: This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Nuclear Physics Division of the U.S. DOE under Contract DE AC03-76SF00098.

The driver linac of the proposed Rare Isotope Accelerator (RIA) requires a great variety of high intensity, high charge state ion beams. In order to design and optimize the low energy beam line optics of the RIA front end, we have developed a new parallel three-dimensional model to simulate the low energy, multi-species beam transport from the ECR ion source extraction region to the focal plane of the analyzing magnet. A multi-section overlapped computational domain has been used to break the original transport system into a number of independent subsystems. Within each subsystem, macro-particle tracking is used to obtain the charge density distribution in this subdomain. The three-dimensional Poisson equation is solved within the subdomain and particle tracking is repeated until the solution converges. Two new Poisson solvers based on a combination of the spectral method and the multigrid method have been developed to solve the Poisson equation in cylindrical coordinates for the beam extraction region and in the Frenet-Serret coordinates for the bending magnet region. Some test examples and initial applications will also be presented.

 
TPPE011 A Compact High-Brightness Heavy-Ion Injector 1263
 
  • G.A. Westenskow, D.P. Grote, E. F. Halaxa
    LLNL, Livermore, California
  • F.M. Bieniosek, J.W. Kwan
    LBNL, Berkeley, California
 
  Funding: This work has been performed under the auspices of the U.S. DOE by UC-LBNL under contract DE-AC03-76SF00098 and by UC-LLNL under contract W-7405-ENG-48, for the Heavy Ion Fusion Virtual National Laboratory.

To provide compact high-brightness heavy-ion beams for Heavy Ion Fusion (HIF) accelerators, we have been experimenting with merging multi-beamlets in an injector which uses an RF plasma source. In an 80-kV 20-microsecond experiment, the RF plasma source has produced up to 5 mA of Ar+ in a single beamlet. An extraction current density of 100 mA/cm2 was achieved, and the thermal temperature of the ions was below 1 eV. More than 90% of the ions were in the Ar+ state, and the energy spread from charge exchange was found to be small. We have tested at full voltage gradient the first 4 gaps of a 61-beamlet injector design. Einzel lens were used to focus the beamlets while reducing the beamlet to beamlet space charge interaction. We will report on a converging 119 multi-beamlet source. Although the source has the same optics as a full 1.6 MV injector system, the test will be carried out at 400 kV due to the test stand HV limit. We will measure the beam’s emittance after the beamlets are merged and have been transported through an electrostatic quadrupole. Our goal is to confirm the emittance growth and to demonstrate the technical feasibility of building a driver-scale HIF injector.

 
TPPE012 Using the Orbit Tracking Code Z3CYCLONE to Predict the Beam Produced by a Cold Cathode PIG Ion Source for Cyclotrons under DC Extraction 1297
 
  • E.R. Forringer, H.G. Blosser
    NSCL, East Lansing, Michigan
 
  Experimental measurements of the emittance and luminosity of beams produced by a cold-cathode Phillips Ionization Guage (PIG) ion source for cyclotrons under dc extraction are reviewed. (The source being studied is of the same style as ones that will be used in a series of 250 MeV proton cyclotrons being constructed for cancer therapy by ACCEL Inst, Gmbh, of Bergisch Gladbach, Germany.) The concepts of 'plasma boundary' and 'plasma temperature' are presented as a useful set of parameters for describing the initial conditions used in computational orbit tracking. Experimental results for r-pr and z-pz emittance are compared to predictions from the MSU orbit tracking code Z3CYCLONE with results indicating that the code is able to predict the beam produced by these ion sources with adequate accuracy such that construction of actual cyclotrons can proceed with reasonably prudent confidence that the cyclotron will perform as predicted.  
TPPE013 Simulations of Solenoid and Electrostatic Quadrupole Focusing of High Intensity Beams from ECR Ion Source at NSCL 1336
 
  • Q. Zhao, A.I. Balabin, M. Doleans, F. Marti, J.W. Stetson, X. Wu
    NSCL, East Lansing, Michigan
 
  Solenoidal focusing has been widely used to focus beams at various injectors for its axisymmetric focusing with reasonable effectiveness. Experiments and simulations have shown that space charge effects can significantly deteriorate the beam quality when solenoidal focusing is used in a multi-component beam. This is due to the magnetic focusing strength dependence on the beam charge-to-mass ratio. Electrostatic quadrupole focusing has been explored as an alternate option at NSCL for the injection line of the superconducting cyclotron. We present in this paper the results of simulations for both systems. The electrostatic quadrupoles have been optimized to reduce the radial dependent aberrations and to increase the transmission efficiency.  
TPPE015 The Effusive-Flow Properties of Target/Vapor-Transport Systems for Radioactive Ion Beam Applications 1422
 
  • Y. Kawai, G. Alton, Y. Liu
    ORNL, Oak Ridge, Tennessee
 
  Funding: Research at ORNL is supported by the U.S. DOE under contract DE-AC05-00OR22725 with UT-Battelle, LLC.

Radioactive atoms produced by the ISOL technique must diffuse from a target, effusively flow to an ion source, be ionized, be extracted, and be accelerated to research energies in a time commensurate with the lifetime of the species of interest. We have developed a fast valve system (closing time ~100 us) that can be used to accurately measure the effusion times of chemically active or inactive species through arbitrary geometry and size vapor transport systems with and without target material in the reservoir. The effusive flow times are characteristic of the system and thus serve as figures of merit for assessing the quality of a given vapor transport system as well as for assessing the permeability properties of a given target design. This article presents effusive flow data for noble gases flowing through a target reservoir and ion source system routinely used to generate radioactive species at the HRIBF with and without disks of 6 times and 10 times compressed Reticulated Vitreous Carbon Foam (RVCF) with the objective of determining the added delay time associated with each of these target matrices.

 
TPPE016 ISOL Targets Prepared with a New Paint Infiltration Coating Method 1508
 
  • Y. Kawai, G. Alton, J. O. Kiggans, D.W. Stracener
    ORNL, Oak Ridge, Tennessee
 
  Funding: Research at ORNL is supported by the U.S. DOE under contract DE-AC05-00OR22725 with UT-Battelle, LLC.

A new infiltration paint coating method has been developed for fabricating ISOL targets for radioactive ion beam applications. The technique has been shown to be inexpensive, fast, and almost universal for the uniform deposition of many refractory target materials onto the interior surfaces of complex geometry matrices, such as Reticulated-Vitreous-Carbon-Foam (RVCF). The process yields robust, highly permeable targets with fast diffusion and release properties. We demonstrate the viability of the technique for coating forms of RVCF compressed by factors of 6 and 10 with materials to form targets for use at high energy facilities such as RIA. The use of compressed RVCF, coated with an optimum thickness of target material, reduces target lengths to practical values, while preserving high permeability. We calculate thermal conductivities and diffusion for various targets on 6xRVCF and 10xRVCF.

 
TPPE017 A New Broadband Microwave Frequency Device for Powering ECR Ion Sources 1529
 
  • Y. Kawai, G. Alton, Y. Liu
    ORNL, Oak Ridge, Tennessee
 
  Funding: Research at ORNL is supported by the U.S. DOE under contract DE-AC05-00OR22725 with UT-Battelle, LLC.

The multiple discrete frequency technique has been used to improve the performance of conventional B-field configuration ECR ion sources. However, the practical application of this technique is very costly, requiring multiple independent single-frequency rf power supplies and complicated rf injection systems. Broadband sources of rf power offer a low-cost and more effective method for increasing the physical size of the ECR zone within these ion sources. An Additive White Gaussian Noise Generator (AWGNG) system for injecting broadband rf power into these ion sources has been developed in conjunction with a commercial firm. The noise generator, in combination with an external oscillator and a traveling wave tube amplifier, can be used to generate broadband rf power without modifying the injection system. The AWGNG and its use for enhancing the performance of conventional B-field configuration ECR ion sources will be described.

 
TPPE018 Characterization of a Tubular Hot-Cavity Surface Ionization Source 1581
 
  • Y. Liu, H. Z. Bilheux, Y. Kawai
    ORNL, Oak Ridge, Tennessee
 
  Funding: Managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725.

Elements with low ionization potentials can be efficiently ionized by positive surface ionization. It has been experimentally observed and theoretically shown that the ionization efficiency in a hot-cavity can be significantly higher than expected for the surface ionization mechanism. This is explained by the existence of a thermal plasma inside the cavity consisting of surface ionized ions and thermionic electrons. We have investigated the suggested ioniation mechanisms in a tubular hot-cavity surface ionization source where the area of the exit aperture is small compared with the tube inner surface. Thermal analyses of the tubular cavity and calculated mean number of wall collisions of a neutral particle in the cavity before escaping through the exit aperture are presented. Measured emittance and ionization efficiencies of various elements as a function of the cavity temperature for different cavity materials are discussed.

 
TPPE019 Laser Ion Source Development for ISOL Systems at RIA 1640
 
  • Y. Liu, C. Baktash, J.R. Beene, H. Z. Bilheux, C.C. Havener, H.F. Krause, D.R. Schultz, D.W. Stracener, C.R. Vane
    ORNL, Oak Ridge, Tennessee
  • K. Brueck, Ch. Geppert, T. Kessler, K. Wendt
    Johannes Gutenberg University Mainz, Mainz
 
  Funding: Managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725.

The isobaric purity of radioactive ion beams (RIBs) is of crucial importance to many experiments. Laser ion sources based on resonant photoionization have already proved to be of great value at existing ISOL RIB facilities. In these ion sources, ions of a selected isotope are produced by laser radiation via stepwise atomic resonant excitations followed by ionization in the last transition. Because each element has its own unique atomic energy levels, the resonant photoionization process can provide elemental selectivity of nearly 100%. We have initiated a research effort to develop a prototype laser ion source with the potential to achieve the high selectivity and high efficiency required for research with ISOL-generated RIBs at the Rare Isotope Accelerator (RIA). A pilot experiment has been conducted to demonstrate resonant photoionization of three atomic species using all-solid-state tunable Ti:Sapphire lasers. Three Ti:Sapphire lasers were provided by the University of Mainz and used in the experiment for three-photon resonant ionization of the elements. Laser generated Sn, Ni, and Ge ions have been successfully obtained in a hot-cavity laser ion source with overall efficiencies of 22%, 2.7%, and 3.3%, respectively.

 
TPPE020 Radioactive Ion Beam Development at the Holifield Radioactive Ion Beam Facility
 
  • D.W. Stracener, G. Alton, J.R. Beene, H. Z. Bilheux, J.-C. Bilheux, J.C. Blackmon, D. Dowling, R.C. Juras, Y. Kawai, Y. Liu, M.J. Meigs, P.E. Mueller, B. A. T. Tatum
    ORNL, Oak Ridge, Tennessee
  • H.K. Carter, A. Kronenberg, E.H. Spejewski
    Center of Excellence for RIB Studies for Stewardship Science, Oak Ridge Associated Universities, Oak Ridge, Tennessee
 
  Funding: Managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725.

Radioactive beams are produced at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory using the Isotope Separator On-Line (ISOL) technique. Radioactive nuclei are produced in a thick target via irradiation with energetic light ions (protons, deuterons, helium isotopes) and then post-accelerated to a few MeV/nucleon for use in nuclear physics experiments. An overview of radioactive beam development at the HRIBF will be presented, including ion source development, improvements in the ISOL production targets, and a description of techniques to improve the quality (intensity and purity) of the beams. Facilities for radioactive ion beam development include two ion source test facilities, a target/ion source preparation and quality assurance facility, and an in-beam test facility where low intensity production beams are used. A new test facility, the High Power Target Laboratory, will be available later this year. At this facility, high intensity production beams will be available to measure the power-handling capabilities of ISOL production targets. This information will be used to optimize target materials and geometries for high power densities.

 
TPPE021 Simulation Studies of Diffusion-Release and Effusive-Flow of Short-Lived Radioactive Isotopes 1739
 
  • Y. Zhang, G. Alton, Y. Kawai
    ORNL, Oak Ridge, Tennessee
 
  Funding: Research supported by the U.S. DOE under contract DE-AC05-00OR22725 with UT-Battelle, LLC.

Delay times associated with diffusion release from targets and effusive-flow transport of radioactive isotopes to ion sources are principal intensity limiters at ISOL-based radioactive ion beam facilities, and simulation studies with computer models are cost effective methods for designing targets and vapor transport systems with minimum delay times to avoid excessive decay losses of short lived ion species. A finite difference code, Diffuse II, was recently developed at the Oak Ridge National Laboratory to study diffusion-release of short-lived species from three principal target geometries. Simulation results are in close agreement with analytical solutions to Fick’s second equation. Complementary to the development of Diffuse II, the Monte-Carlo code, Effusion, was developed to address issues related to the design of fast vapor transport systems. Results, derived by using Effusion, are also found to closely agree with experimental measurements. In this presentation, the codes will be used in concert to make realistic estimations of intensities of a number of short-lived isotopes that are candidates for use in future nuclear physics and nuclear astrophysics experiments at the HRIBF.

 
TPPE022 First Results on the Path Towards a Microwave-Assisted H- Ion Source 1784
 
  • R. Keller, P.A. Luft, M. T. Monroy, A. Ratti, M.J. Regis, D. L. Syversrud, J.G. Wallig
    LBNL, Berkeley, California
  • D.E. Anderson, R.F. Welton
    ORNL, Oak Ridge, Tennessee
 
  Funding: This work supported by Office of Basic Energy Sciences, U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

A novel concept for creating intense beams of negative hydrogen ion beams is presented. In this approach, an ECR ion source operating at 2.45 GHz frequency is utilized as a primary plasma generator and coupled to an SNS-type multi-cusp H- ion source. The secondary source is driven by chopped dc power avoiding the use of filaments or of an internal rf antenna. The development of the new ion source is aimed at the future beam-power goal of 3 MW for the Spallation Neutron Source (SNS) that will be pursued after the start of SNS operations, but application to other proton driver accelerators that include an accumulator ring is feasible as well. The first two phases of this development effort have been successfully completed: assembly of a test stand and verification of the performance of an rf-driven SNS ion-source prototype; and extraction of electrons with more than 350 mA current from a 2.45-GHz ECR ion source obtained on loan from Argonne National Laboratory. The next goal is the demonstration of actual H- ion production by this novel, hybrid ion source. This paper describes the source principle and design in detail and reports on the current status of the development work.

 
TPPE023 Development and Performance of a Proton and Deuteron ECR Ion Source
 
  • K. Dunkel, F. Kremer, C. Piel, J. Plitzko
    ACCEL, Bergisch Gladbach
 
  A 5mA proton and deuteron rf source is under development at ACCEL. This source will provide the front end of our superconducting proton/deuteron linear accelerator. The design of the source is based on the proven AECL design of a 100 mA proton source. The paper will describe the design of the source and the layout of the test bench currently set up at ACCEL to characterize the source. Results of the beam dynamic simulations performed to optimize the source geometry based on KOBRA 3D will be presented and compared with first measurement results.  
TPPE025 Separating the Penning and Analysing Fields in the ISIS H- Ion Source 1910
 
  • D.C. Faircloth, R. Sidlow, M. Whitehead, T.W. Wood
    CCLRC/RAL/ISIS, Chilton, Didcot, Oxon
 
  Funding: This work was supported by the European Union High Performance Negative Ion Source (HP-NIS) network, contract number HPRI-CT-2001-50021.

The development of H- ion sources with performances exceeding those achieved today is a key requirement for the next generation of high power proton accelerators. The Penning surface plasma source development program at ISIS is now well established. To allow different ion source designs to be fully tested, the ability to vary the Penning field is required. Until now the Penning field has been generated by the same magnetic circuit that creates the analyzing field, giving no practical way of altering the Penning field alone. This paper describes the infrastructure changes required to allow the Penning field to be independently varied. The effect the Penning field has on beam current, emittance and discharge stability are discussed.

 
TPPE027 Properties of Laser-Produced Highly Charged Heavy Ions for Direct Injection Scheme 1976
 
  • K. Sakakibara, T. Hattori, N. Hayashizaki, T. Ito
    RLNR, Tokyo
  • H. Kashiwagi
    JAERI/ARTC, Gunma-ken
  • M. Okamura
    RIKEN, Saitama
 
  To accelerate highly charged intense ion beam, we have developed the Direct Plasma Injection Scheme (DPIS) with laser ion source. In this scheme an ion beam from a laser ion source is injected directly to a RFQ linac without a low energy beam transport (LEBT) and the beam loss in the LEBT can be avoided. We achieved high current acceleration of carbon ions (60mA) by DPIS with the high current optimized RFQ. As the next setp we will use heavier elements like Ag, Pb, Al and Cu as target in LIS (using CO2, Nd-YAG or other laser) for DPIS and will examine properties of laser-produced plasma (the relationship of between charge state and laser power density, the current dependence of the distance from the target, etc).  
TPPE028 In-Situ Electron Cyclotron Resonance (ECR) Plasma Potential Determination Using an Emissive Probe 2035
 
  • F.W. Meyer, Y. Liu
    ORNL, Oak Ridge, Tennessee
  • H.J. You
    Hanyang University, Seoul
 
  Funding: This research was sponsored by the U.S. DOE under contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. HJY acknowledges support from the Korean Science Education Foundation (KOSEF).

In this paper, real-time, in-situ, plasma potential measurements are reported for an ECR ion source and correlated with extracted beam characteristics. The local real-time plasma potential of the ORNL CAPRICE ECR ion source was measured using an emissive probe, which was inserted perpendicularly from the plasma chamber wall at the mid-plane of the ECR zone between one of the six radial loss cones of the magnetic field structure, where perturbation of the main ECR plasma is expected to be small. Slots machined through the plasma- and puller-electrodes at the plasma chamber wall radius permitted insertion of the probe from the extraction side of the ECR source without perturbation of the coaxial microwave injection. The emissive probe technique permits plasma potential determination independent of plasma conditions and avoids problems related to probe geometry. The probe loop tip was pointed toward the chamber center in a radial plane and was located about 5 mm outside of the ECR zone. Details of the measurements, and a comparison with an external-beam-deceleration-based plasma potential determination will be presented.

 
TPPE029 Measurements of Ion Selective Containment on the RF Charge Breeder Device BRIC 2065
 
  • V. Variale, A. Boggia, T. Clauser, A. Rainò, V. Valentino
    INFN-Bari, Bari
  • P.A. Bak, M. A. Batazova, G.I. Kuznetsov, S. Shiyankov, B.A. Skarbo
    BINP SB RAS, Novosibirsk
  • G. Verrone
    Università e Politecnico di Bari, Bari
 
  Funding: Istituto Nazionale Fisica Nucleare.

The "charge state breeder" BRIC (BReeding Ion Charge) is based on an EBIS source and it is designed to accept Radioactive Ion Beam (RIB) with charge +1, in a slow injection mode, to increase their charge state up to +n. BRIC has been developed at the INFN section of Bari (Italy) during these last 3 years with very limited funds. Now, it has been assembled at the LNL (Italy) where are in progress the first tests as stand alone source. The new feature of BRIC, with respect to the classical EBIS, is given by the insertion, in the ion drift chamber, of a Radio Frequency (RF) Quadrupole aiming to filtering the unwanted elements and then making a more efficient containment of the wanted ions. In this contribution, the measurements of the selective effect on the ion charge state containement of the RF quadrupole field, applied on the ion chamber, will be reported and discussed. The ion charge state analisys of the ions trapped in BRIC seem confirm, as foreseen by simulation results carried out previously, that the selective containment can be obtained. A modification of the collector part to improve the ion extraction of BRIC will be also presented and shortly discussed.

 
TPPE030 A Method to Polarize Stored Antiprotons to a High Degree 2158
 
  • A. Lehrach, S. Martin, F. Rathmann
    FZJ, Jülich
  • P. Lenisa
    INFN-Ferrara, Ferrara
  • I.N. Meshkov, A.O. Sidorin, A.V. Smirnov
    JINR, Dubna, Moscow Region
  • C. Montag
    BNL, Upton, Long Island, New York
  • E. Steffens
    University of Erlangen-Nürnberg, Physikalisches Institut II, Erlangen
  • C.-A. Wiedner
    UGS, Langenbernsdorf
 
  The PAX collaboration proposes a method to produce intense beams of polarized antiprotons. Polarized antiprotons can be produced in a storage ring by spin-dependent interaction in a purely hydrogen gas target. The polarizing process is based on spin transfer from the polarized electrons of the target atoms to the orbiting antiprotons. After spin filtering for about two beam lifetimes at energies of about 50-100 MeV using a dedicated large acceptance ring, the antiproton polarization would reach P=0.2-0.4. In the presentation, beside a description of the polarization technique and its potentiality, a description of the ideal characterstics of the antiproton polarizer will be given.

hep-ph/0411046

 
TPPE031 60 mA Carbon Beam Acceleration with DPIS 2206
 
  • M. Okamura, R.A. Jameson, K. Sakakibara, J. Takano
    RIKEN, Saitama
  • T. Fujimoto, S. Shibuya, T. Takeuchi
    AEC, Chiba
  • Y. Iwata, K. Yamamoto
    NIRS, Chiba-shi
  • H. Kashiwagi
    JAERI/ARTC, Gunma-ken
  • A. Schempp
    IAP, Frankfurt-am-Main
 
  We have studied "direct plasma injection scheme (DPIS)" since 2000. This new scheme is for producing very intense heavy ions using a combination of an RFQ and a laser ion source. An induced laser plasma goes directly into the RFQ without an extraction electrode nor any focusing devices. Obtained maximum peak current of Carbon 4+ beam reached 60 mA with this extremely simple configuration. The details of the experimental result will be presented.  
TPPE032 Particle-in-Cell Simulations of the VENUS Ion Beam Transport System 2236
 
  • D.S. Todd, D. Leitner, C.M. Lyneis, J. Qiang
    LBNL, Berkeley, California
  • D.P. Grote
    LLNL, Livermore, California
 
  Funding: This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Nuclear Physics Division of the U.S. DOE under Contract DE AC03-76SF00098

The next-generation superconducting ECR ion source VENUS serves as the prototype injector ion source for the linac driver of the proposed Rare Isotope Accelerator (RIA). The high-intensity heavy ion beams required by the RIA driver linac present significant challenges for the design and simulation of an ECR extraction and low energy ion beam transport system. Extraction and beam formation take place in a strong (up to 3T) axial magnetic field, which leads to significantly different focusing properties for the different ion masses and charge states of the extracted beam. Typically, beam simulations must take into account the contributions of up to 30 different charge states and ion masses. Two three-dimensional, particle-in-cell codes developed for other purposes, IMPACT and WARP, have been adapted in order to model intense, multi-species DC beams. A discussion of the differences of these codes and the advantages of each in the simulation of the low energy beam transport system of an ECR ion source is given. Direct comparisons of results from these two codes as well as with experimental results from VENUS are presented.

 
TPPE033 A Comparison of Electrostatic and Magnetic Focusing of Mixed Species Heavy Ion Beams at NSCL/MSU 2281
 
  • J.W. Stetson, G. Machicoane, F. Marti, P. Miller, M. Steiner, P.A. Zavodszky
    NSCL, East Lansing, Michigan
  • Yu. Kazarinov
    JINR, Dubna, Moscow Region
 
  Funding: This work has been supported by National Science Foundation under grant PHY-0110253.

Experience at the National Superconducting Cyclotron Laboratory has shown the first focusing element after the electron cyclotron resonance ion source (ECRIS), before the beam is analyzed by a magnetic dipole, to be critical to subsequent beam transport and matching. Until 2004, both ion sources at the NSCL used a solenoid as this first focusing element. Observation of hollow beam formation led to further analysis and the decision to replace the solenoid with an electrostatic quadrupole triplet on a test basis [1]. Substantial increases in net cyclotron output were achieved, leading us to adopt electrostatic quadrupole focusing as the permanent configuration. In addition, a sextupole magnet was installed in this beam line. Motivations for these changes and results of operating experience are discussed.

 
TPPE034 Possible Scheme of the Analyzing Part of a Cyclotron Injection Beamline with Higher Energy 2345
 
  • Yu. Kazarinov
    JINR, Dubna, Moscow Region
  • J.W. Stetson, P.A. Zavodszky
    NSCL, East Lansing, Michigan
 
  Funding: This work was supported in part by the National Science Foundation under grant PHY-0110253.

The ion beam produced with an ECR ion source (ECRIS) with an extraction voltage of 30 kV may be additionally accelerated using a negative voltage of -30 kV applied to the last electrode of the extraction system, connected to the beamline biased to the same -30 kV potential. In this way the kinetic energy of the beam is increased to 60 keV/q, decreasing to half the space charge effect on the beam emittance. Using a large gap analyzing magnet placed right after the ECRIS and no focusing element, the transmission is still close to 100%. The voltage on the beamline must be kept constant from the ECRIS till the image focal plane of the analyzing magnet where the full separation of the beam charge states is achieved. An insulator break separates the biased beamline from the downstream section, which is at zero potential. Passing through this section of the beamline, the ion beam is decelerated to 30 keV/q, the energy necessary for the injection in the cyclotron. In order to prevent the increase of the beam divergence, a focusing solenoid is installed behind the break point. This work will present the results of a simulation of the transport of an argon beam in the proposed beamline.

 
TPPE035 Efficiency of the Fermilab Electron Cooler’s Collector 2387
 
  • L.R. Prost, A.V. Shemyakin
    Fermilab, Batavia, Illinois
 
  Funding: Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the United States Department of Energy.

The newly installed high-energy Recycler Electron Cooling system (REC) at Fermilab will work at an electron energy of 4.34 MeV and a DC beam current of 0.5 A in an energy recovery scheme. For reliable operation of the system, the relative beam current loss must be maintained to levels < 3.e-5. Experiments have shown that the loss is determined by the performance of the electron beam collector, which must retain secondary electrons generated by the primary beam hitting its walls. As a part of the Electron cooling project, the efficiency of the collector for the REC was optimized, both with dedicated test bench experiments and on two versions of the cooler prototype. We find that to achieve the required relative current loss, an axially-symmetric collector must be immersed in a transverse magnetic field with certain strength and gradient prescriptions. Collector efficiencies in various magnetic field configurations, including without a transverse field on the collector, are presented and discussed

 
TPPE036 Progress of the BEPCII Linac Upgrade 2416
 
  • G. Pei
    IHEP Beijing, Beijing
 
  BEPCII-an upgrade project of the BEPC is a factory type of e+e- collider. It requires its injector linac to have a higher beam energy (1.89 GeV) for on-energy injection and a higher beam current (40 mA e+ beam) for a higher injection rate (=50 mA/min.). The low beam emittance (1.6pmm-mrad for e+ beam, and 0.2pmm-mrad for 300 mA e- beam) and low beam energy spread (±0.5%) are also required to meet the storage ring acceptance. Hence we need a new electron gun system, a new positron source, a much higher power and more stable RF system with its phasing loops, and a new beam tuning system with orbit correction. Up to date, all system design and fabrication work have been completed. And in five months from May 1st of 2004, the positron production system–from the electron gun to the positron source, has been installed into the tunnel. In this paper, we will introduce major upgrades of each system, and present the recent beam commissioning.  
TPPE037 Relative Contribution of Volume and Surface-Plasma Generation of Negative Ions in Gas Discharges 2482
 
  • V.G. Dudnikov
    BTG, New York
 
  The relative contribution of volume and surface-plasma generation of extracted ?- ions in gas discharge sources will be analyzed. At the present time, it is well known that surface-plasma generation of extracted ?- ion is dominate above volume processes in discharges with admixture of cesium or other catalysts with low ionization potential. We will attract attention to evidences, that surface-plasma generation can be enhanced in high density discharges without cesium after electrode activation by high temperature conditioning in discharge. A diffusion of impurity with a low ionization potential can be a reason of observed enhancement of H- emission. For the effective generation of ?- ion beams in discharge without cesium, it is necessary to optimize surface-plasma generation of extracted ?- ion. Such optimization allows considerable improvement of ?-/D- sources characteristics.  
TPPE038 Thermal Hydraulic Design of PWT Accelerating Structures 2524
 
  • D. Yu, A. Baxter, P. Chen, M. Lundquist, Y. Luo
    DULY Research Inc., Rancho Palos Verdes, California
 
  Funding: Work supported by DOE SBIR Grant No. DE-FG02-03ER83846.

Microwave power losses on the surfaces of accelerating structures will transform to heat which will deform the structures if it is not removed in time. Thermal hydraulic design of the disk and cooling rods of a Plane Wave Transformer (PWT) structure is presented. Experiments to measure the hydraulic (pressure vs flow rate) and cooling (heat removed vs flow rate) properties of the PWT disk are performed, and results compared with simulations using Mathcad models and the COSMOSM code. Both experimental and simulation results showed that the heat deposited on the structure could be removed effectively using specially designed water-cooling circuits and the temperature of the structure could be controlled within the range required.

 
TPPE039 Development of Advanced Models for 3D Photocathode PIC Simulations 2583
 
  • D.A. Dimitrov, D.L. Bruhwiler, J.R. Cary, P. Messmer, P. Stoltz
    Tech-X, Boulder, Colorado
  • D.W. Feldman, P.G. O'Shea
    IREAP, College Park, Maryland
  • K. Jensen
    NRL, Washington, DC
 
  Funding: This work is supported by the U.S. DOE, use of NERSC supercomputer facilities, and the Joint Technology office (JTO).

Codes for simulating photocathode electron guns invariably assume the emission of an idealized electron distribution from the cathode, regardless of the particular particle emission model that is implemented. The output of such simulations, a relatively clean and smooth distribution with very little variation as a function of the azimuthal angle, is inconsistent with the highly irregular and asymmetric electron bunches seen in experimental diagnostics. To address this problem, we have implemented a recently proposed theoretical model* that takes into account detailed solid-state physics of photocathode materials in the VORPAL particle-in-cell code.** Initial results from 3D simulations with this model and future research directions will be presented and discussed.

*K.L. Jensen, D.W. Feldman, M. Virgo, and P.G. O'Shea, Phys. Rev. ST Accel. Beams, 6:083501, 2003. **C. Nieter and J.R. Cary, J. Comp. Phys. 196 (2004), p. 448.

 
TPPE040 RF and Magnetic Measurements on the SPARC Photoinjector and Solenoid at UCLA 2624
 
  • J.B. Rosenzweig, A.M. Cook, M.P. Dunning, P. Frigola, G. Travish
    UCLA, Los Angeles, California
  • D.T. Palmer
    SLAC, Menlo Park, California
  • C. Sanelli, F. Tazzioli
    INFN/LNF, Frascati (Roma)
 
  Funding: This work is supported by U.S. Dept. of Energy grant DE-FG03-92ER40693.

The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center.

 
TPPE041 Multi-Alkali Photocathode Development at Brookhaven National Lab for Application in Superconducting Photoinjectors 2672
 
  • A. Burrill, I. Ben-Zvi, D. Pate, T. Rao, Z. Segalov
    BNL, Upton, Long Island, New York
  • D. Dowell
    SLAC, Menlo Park, California
 
  In this paper we will report our progress on the development of cesium potassium antimonide photocathodes and their application in superconducting photoinjectors. Quantum efficiencies of 2-3 % at 545 nm, and 10% at 365 nm have been routinely obtained in the test stand, and electron emission uniformity, quantum efficiency at a variety of wavelengths, and lifetime under different vacuum conditions has been well characterized. The extraction of high charge per laser pulse will also be addressed in addition to the comparison of results from two different deposition techniques.  
TPPE042 Study of Secondary Emission Enhanced Photoinjector 2711
 
  • X.Y. Chang, I. Ben-Zvi, A. Burrill, P.D.J. Johnson, J. Kewisch, T. Rao, Z. Segalov, Y. Zhao
    BNL, Upton, Long Island, New York
 
  The secondary emission enhanced photoinjector (SEEP) is a very promising new approach to the generation of high-current, high-brightness electron beams. Primary electrons with a few thousand electron-volts of energy strike a specially prepared diamond window. The large Secondary Electron Yield (SEY) provides a multiplication of the number of electrons by about two orders of magnitude. The secondary electrons drift through the diamond under an electric field and emerge into the accelerating proper of the “gun” through a Negative Electron Affinity (NEA) surface of the diamond (Hydrogen terminated). We present the calculation of heating power sources and the temperature distribution in details. Some properties of the secondary electron beam related to beam dynamics are also reported. The results show feasibility of this kind of cathode.  
TPPE043 Electron Beam Generation and Transport for the RHIC Electron Cooler 2774
 
  • J. Kewisch, I. Ben-Zvi, X.Y. Chang
    BNL, Upton, Long Island, New York
 
  Funding: Work performed under Contract Number DE-AC02-98CH10886 with the auspices of the U.S. Department of Energy.

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. A better understanding of the cooling process and more accurate measurements of Intra Beam Scattering in RHIC have imposed increased requirements on the electron accelerator: Besides a doubling of the bunch charge to 20 nC, the strength of the cooling solenoid was increased five-fold to 5 Tesla. The magnetic field on the cathode should be increased to 500 Gauss to match the magnetization required in the cooling solenoid. This paper reports the measures taken to minimize the electron beam emittance in the cooling section. The front-to-end simulation using different tracking codes is presented.

 
TPPE044 Upgrade of the Fermilab/NICADD Photoinjector Laboratory 2848
 
  • P. Piot, H. Edwards
    Fermilab, Batavia, Illinois
  • M. Huening
    DESY, Hamburg
  • T. W. Koeth
    Rutgers University, The State University of New Jersey, Piscataway, New Jersey
  • J.L. Li, R. Tikhoplav
    Rochester University, Rochester, New York
 
  Funding: This work was supported by Universities Research Association Inc. under contract DE-AC02-76CH00300 with the U.S. DOE, and by NICADD.

The Femilab/NICADD photoinjector laboratory (FNPL) is a 16 MeV electron accelerator dedicated to beam dynamics and advanced accelerator studies. FNPL will soon be capable of operating at 50 MeV, after the installation of a high gradient TESLA cavity. In this paper we present the foreseen design for the upgraded facility along with its performance. We discuss the possible application of 50 MeV beam including the possible use of FNPL as an injector for the superconducting module and test facility (SM&TF).

 
TPPE045 Normal-Conducting High Current RF Photoinjector for High Power CW FEL 2866
 
  • S.S. Kurennoy, D.C. Nguyen, D.L. Schrage, R.L. Wood
    LANL, Los Alamos, New Mexico
  • V. Christina, J. Rathke, T. Schultheiss
    AES, Medford, NY
  • L.M. Young
    TechSource, Santa Fe, New Mexico
 
  An RF photoinjector capable of producing high average current with low emittance and energy spread is a key enabling technology for high power CW FEL. The design of a 2.5-cell, pi-mode, 700-MHz normal-conducting RF photoinjector cavity with magnetic emittance compensation is completed. With average gradients of 7, 7, and 5 MV/m in its three accelerating cells, the photoinjector will produce a 2.5-MeV electron beam with 3-nC charge per bunch and transverse rms emittance below 7 mm-mrad. Electromagnetic modeling has been used extensively to optimize ridge-loaded tapered waveguides and RF couplers, and led to a new, improved coupler iris design. The results, combined with a thermal and stress analysis, show that the challenging problem of cavity cooling can be successfully solved. Fabrication of a demo 100-mA (at 35 MHz bunch repetition rate) photoinjector is underway. The design is scalable to higher average currents by increasing the electron bunch repetition rate, and provides a path to a MW-class FEL. This paper presents the cavity design and details of RF coupler modeling.  
TPPE046 Computer Simulation of the UMER Gridded Gun 2908
 
  • I. Haber, S. Bernal, R.A. Kishek, P.G. O'Shea, Y. Zou
    IREAP, College Park, Maryland
  • A. Friedman, D.P. Grote
    LLNL, Livermore, California
  • M. Reiser
    University Maryland, College Park, Maryland
  • J.-L. Vay
    LBNL, Berkeley, California
 
  Funding: This work is supported by the U.S. DOE under contract Nos. DE-FG02-02ER54672 and DE-FG02-94ER40855 at the UMD, and DE-AC03-76SF00098 at LBNL and W-7405-ENG-48 at LLNL.

The electron source in the University of Maryland Electron Ring (UMER) injector employs a grid 0.15 mm from the cathode to control the current waveform. Under nominal operating conditions, the grid voltage during the current pulse is sufficiently positive relative to the cathode potential to form a virtual cathode downstream of the grid. Three-dimensional computer simulations have been performed that use the mesh refinement capability of the WARP particle-in-cell code to examine a small region near the beam center in order to illustrate some of the complexity that can result from such a gridded structure. These simulations have been found to reproduce the hollowed velocity space that is observed experimentally. The simulations also predict a complicated time-dependent response to the waveform applied to the grid during the current turn-on. This complex temporal behavior appears to result directly from the dynamics of the virtual cathode formation and may therefore be representative of the expected behavior in other sources, such as some photoinjectors, that are characterized by a rapid turn-on of the beam current.

 
TPPE047 Fabrication and Measurement of Low Work Function Cesiated Dispenser Photocathodes 2953
 
  • N.A. Moody, D.W. Feldman, P.G. O'Shea
    IREAP, College Park, Maryland
  • K. Jensen
    NRL, Washington, DC
 
  Funding: We gratefully acknowledge our funding agencies, the Joint Technology Office and the Office of Naval Research for their support.

Photoinjector performance is a limiting factor in the continued development of high powered FELs and electron beam-based accelerators. Presently available photocathodes are plagued with limited efficiency and short lifetime in an RF-gun environment, due to contamination or evaporation of a photosensitive surface layer. An ideal photocathode should have high efficiency at long wavelengths, long lifetime in practical vacuum environments, and prompt emission. Cathodes with high efficiency typically have limited lifetime, and vice versa, and the needs of the photocathode are generally at odds with those of the drive laser. A potential solution is the low work function dispenser cathode, where lifetime issues are overcome by periodic in situ regeneration that restores the photosensitive surface layer, analogous to those used in the microwave power tube industry. This work reports on the fabrication techniques and performance of cesiated metal photocathodes and cesiated dispenser cathodes, with a focus on understanding and improving quantum efficiency and lifetime, and analyzing issues of emission uniformity. The efficiency versus coverage behavior of cesiated metals is discussed and closely matches that predicted by recent theory.*

*K. L. Jensen, et al., "Photoemission from Low Work Function Coated Metal Surfaces: A Comparison of Theory to Experiment" (this conference).

 
TPPE048 The Injection System of SAGA Light Source 3007
 
  • Y. Iwasaki, S. Koda, T. Okajima, Y. Takabayashi, T. Tomimasu, K. Yoshida
    Saga Synchrotron Light Source, Industry Promotion Division, Saga City
  • H. Ohgaki
    Kyoto IAE, Kyoto
 
  Saga light Source is a 1.4-GeV electron storage ring with a circumference of 75.6m. The injector is a 250-MeV linac producing 1 ms macro-pulse with a peak current of 12mA and repetition rate of 1Hz. The output beam from the linac is transported though a transport line, and injected into the ring though a septum magnet with a bending angle of 20-degree. The transport line consists of two bending magnets, two quadrupole doublelets, and a quadrupole singlet. The bump orbit is formed by four kicker magnets, two of which are installed at both sides of septum magnet, and other two are positioned apart by one magnet cell of the ring. They are excited by sinusoidal electric currents with a half width of 0.5 ms. The beam optics for the injection trajectory is computed and shown at control room, the parameters for which are provided directly from the power supply control server PC. The operator is able to see real-time result of the beam trajectory calculation. This tool is quite effective to optimize the magnets parameter setting. The commissioning of the light source was started in August 2004, and 250-MeV electrons ware stored first time on November 2004.  
TPPE049 Synchronizaiton Between Laser and Electron Beam at Photocathode RF Gun 3079
 
  • A. Sakumi, A. Fukasawa, Y. Muroya, T. Ueda, M. Uesaka, K. Yoshii
    UTNL, Ibaraki
  • K. Dobashi
    NIRS, Chiba-shi
  • N. Kumagai, H. Tomizawa
    JASRI/SPring-8, Hyogo
  • J.U. Urakawa
    KEK, Ibaraki
 
  The chemical reactions of hot, room temperature and critical water in a time-range of picosecond and sub-picosecond have been carried out by the 18 MeV S-band linac and a Mg photocathode RF gun with the irradiation of third harmonic Ti: Sapphire laser, at Nuclear Engineering Research Laboratory (NERL), the University of Tokyo. Although this short bunch and 100 fs laser light are enough to perform the experiment of radiation chemistry in the time-range of sub-picosecond, the total time-resolution become worse by the instability of synchronization between laser and radio frequency of linac. We found that the fluctuation of room temperature causes the instability, particularly the cycle of turning on/off of the air-conditioner. It is shown that 0.3 °C (peak-to-peak) fluctuation of the laser-room temperature have approximately corresponded to the instability of 6 ps. We are trying to decrease the fluctuation of the room temperature, together with the local temperature stability of the Ti: Sapphire crystal, the pumping laser. Furthermore, we will develop the feed back system for reducing the instability of the synchronization.  
TPPE050 Beam Injection in Recirculator SALO 3109
 
  • I.S. Guk, A. Dovbnya, S.G. Kononenko, F.A. Peev, A.S. Tarasenko
    NSC/KIPT, Kharkov
  • J.I.M. Botman, M.J. Van der Wiel
    TUE, Eindhoven
 
  Possible antetypes of injectors for electron recirculator SALO,* intended for nuclear-physical research, are analyzed. The plan injection of beams in recirculator is offered. Expected parameters of beams are designed.

*I.S. Guk, A.N. Dovbnya, S.G. Kononenko, A.S. Tarasenko, M. van der Wiel, J.I.M. Botman, NSC KIPT accelerator on nuclear and high energy physics, Proceedings of EPAC 2004, Lucerne, Switzerland, p. 761-764.

 
TPPE051 The Optimization of the Electron Injector Resonance System Based on the Evanescent Oscillations 3170
 
  • S.A. Perezhogin, M.I. Ayzatskiy, K. Kramarenko, V.A. Kushnir, V.V. Mytrochenko, Z.V. Zhiglo
    NSC/KIPT, Kharkov
 
  The report presents the results of the bunching system optimization and electrons motion simulation in the compact S – band injector. The injector consists of the low-voltage diode electron gun and optimized bunching system based on the resonant system with the evanescent oscillations. The amplitude of RF electrical field is increased along the axis of the bunching system. The resonance system optimization allows to obtain electron bunches with the phase length less than 10° (for 70 % particles) at the injector exit.  
TPPE052 Characteristics of Electron Beam Produced by Magnetron Diode with a Secondary-Emission Cathode 3197
 
  • N.G. Reshetnyak, N. Aizatsky, A. Dovbnya, N.A. Dovbnya, V.V. Mytrochenko, V. Zakutin
    NSC/KIPT, Kharkov
 
  The beam parameters were investigated using an azimuth-sectionalized 8-channel Faraday cup and a 12-channel computer-aided measuring system. The magnetron diode had a cathode (40 mm in diameter) and a 15 mm anode-cathode gap. At a cathode voltage amplitude of 50 kV and a cathode magnetic field of ~1200 Oe, the diode generates a tubular electron beam with an outer diameter of 50 mm, an inner diameter of 44 mm, a beam current of ~50 A. The short time instability of the total beam current, and of the current from each of eight segments of the Faraday cup was estimated to be ~2 … 3%, and long time instability (3 hours) was 57 %. Azimuthal distribution of beam current was investigated versus the amplitude, distribution and direction of the magnetic field. At a cathode magnetic field of 1200 Oe, that falls off inhomogeneity in the vicinity of the Faraday cup down to ~800 Oe, the azimuthal beam current distribution has a ± (3 … 5)%. As the magnetic field strength increases up to ~1700 Oe in the region of beam emergence from the gun and the Faraday cup, the azimuthal inhomogeneity of the beam current increases up to ± (100 … 150)%.  
TPPE053 Design Issues for the ILC Positron Source 3230
 
  • V. Bharadwaj, Y.K. Batygin, R. Pitthan, D.C. Schultz, J. Sheppard, H. Vincke, J.W. Wang
    SLAC, Menlo Park, California
  • J.G. Gronberg, W. Stein
    LLNL, Livermore, California
 
  Funding: Work supported by Department of Energy contract DE-AC02-76SF00515.

A positron source for the ILC can be designed using either a multi-GeV electron beam or a multi-MeV photon beam impinging on a metal target. The major issues are: the drive beam, choice of target material, the design of the target station, the capture section, the target vault, and beam transport to the damping ring. In this paper, positron source parameters for the various schemes are outlined and the advantages and disadvantages of each scheme are discussed.

 
TPPE054 Status of the Injection System for the Australian Synchrotron Project 3271
 
  • S.P. Møller, H. Bach, F. Bødker, T.G. Christiansen, A. Elkjaer, S. Friis-Nielsen, N. Hauge, J. Kristensen, L.K. Kruse, S.P. Møller, B.R. Nielsen
    Danfysik A/S, Jyllinge
 
  DANFYSIK A/S designs and builds the complete injection system for the Australian Synchrotron Project. The full-energy booster will accelerate the beam from the injection energy of 100 MeV. to a maximum of 3.0 GeV. The booster is using combined function magnets. The status of the project is presented.  
TPPE055 DC-SC Photoinjector with Low Emittance at Peking University 3325
 
  • R. Xiang, Y.T. Ding, J. Hao, S.L. Huang, X.Y. Lu, S.W. Quan, B.C. Zhang, K. Zhao
    PKU/IHIP, Beijing
 
  High average power Free Electron Lasers require the high quality electron beams with the low emittance and the sub-picosecond bunches. The design of DC-SC photoinjector, directly combining a DC photoinjector with an SRF cavity, can produce high average current beam with moderate bunch charge and high duty factor. Because of the DC gun, the emittance increases quickly at the beginning, so a carefully design is needed to control that. In this paper, the simulation of an upgraded design has been done to lower the normalized emittance below 1.5mm·mrad. The photoinjector consists of a DC gap and a 2+1/2-cell SRF cavity, and it is designed to produce 4.2 MeV electron beams at 100pC bunch charge and 81.25MHz repetition rate (8 mA average current).  
TPPE056 Emittance Measurement with Upgraded RF Gun System at SPring-8 3348
 
  • A. Mizuno, H. Dewa, H. Hanaki, T. Taniuchi, H. Tomizawa
    JASRI/SPring-8, Hyogo
  • M. Uesaka
    UTNL, Ibaraki
 
  A single cell S-band RFgun has been developed at the SPring-8 since 1996. The minimum normalized beam emittance, measured with double slits' scanning method in 2002, was 2.3 pi mm mrad at the exit of the gun cavity with charge of 0.1 nC/bunch. In 2004, we installed a following accelerator structure to investigate beam behavior of the whole injector system. In this paper, we report emittance measurement results of upgraded system, using variable quadrupole magnet method. The minimum emittance of 2.0 pi mm mrad with a net charge of 0.14 nC/bunch were able to be measured.  
TPPE057 An Experimental Study of the Quantum Efficiency and Topology of Copper Photocathode Due to Plasma Cleaning and Etching
 
  • D.T. Palmer, F. King, R.E. Kirby
    SLAC, Menlo Park, California
 
  We have developed an experimental research program to the study of the photoemission properties of copper photocathodes as a function of various plasma cleaning/etching parameters. The quantum efficiency, QE, and topology, Ra and Rpp, of Copper Photocathodes, , will be monitored while undergoing plasma cleaning/etching process. We will monitor the QE as a function of time for the various test coupons while we optimize the various plasma processing parameters. In addition, surface topology, will be studied to determine the suitability of the cleaning/etching process to produce an acceptable photoemitter. We propose to use two metrics in the evaluation of the plasma cleaning process as an acceptable cleaning method for metallic photocathodes, Quantum Efficiency versus Wavelength and Surface roughness: Ra and Rpp represent the Average Roughness and Peak to Peak Roughness parameters, respectively.  
TPPE058 Dual Feed RF Gun Design for the LCLS 3432
 
  • L. Xiao, R.F. Boyce, D. Dowell, Z. Li, C. Limborg-Deprey, J.F. Schmerge
    SLAC, Menlo Park, California
 
  Funding: Work supported by the U.S. DOE under contract DE-AC03-76SF00515.

In order to remove the dipole field introduced by the coupler in existing S-band BNL/SLAC/UCLA 1.6 cell rf gun, a dual feed design for the LCLS RF gun is proposed together with several significant changes. The improvements include adopting Z-coupling instead of ?-coupling for easier machining and reducing heating, increasing the 0-and ?-mode separation from 3.4 to 15 MHz to reduce the amplitude of the 0 mode, incorporating race-track cavity shape to minimize the quadruple fields, increased cooling for operation at 120Hz and other small changes to improve performance and diagnostic capabilities. The new design has been modeled with the parallel finite element eigenmode solver Omega3P to provide the desired RF parameters and to generate the gun cavity dimensions needed for fabrication.

 
TPPE059 New Electron Gun System for BEPCII
 
  • B. Liu, Y.L. Chi, M. Gu, C. Zhang
    IHEP Beijing, Beijing
 
  The new electron gun system for BEPCII has been put into operation since Nov. 2004. The article describes the design, experiment and operation of this new system. The design current of the gun is 10 A for the pulse lengths of 1 ns, 2.5 ns and 1 μs with repetition rate of 50 Hz. The gun is operated with a pulsed high voltage power supply which can provide up to 200 kV high voltage. Computer simulations have been carried out in the design stage, including simulation of the gun geometry and beam transportation. Some important relation curves are obtained during the experiment. Two-bunch operation is available and some elementary tests have been performed. New scheme of the gun control system based on EPICS is also presented. The real operation shows that the design and manufacturing is basically successful.  
TPPE060 Simulation Study of a Thermionic RF Gun for High Brightness and Short Pulse Beam 3499
 
  • T. Tanaka, H. Hama, F. Hinode, M. Kawai
    LNS, Sendai
  • A. Miyamoto
    HSRC, Higashi-Hiroshima
  • K. Shinto
    Tohoku University, Sendai
 
  Characteristics of thermionic RF guns are not understood completely. In particular, measured intense beam emittances extracted from thermionic RF guns do not agree well with simulated values so far. Most of simulation codes solve the equation of electron motion in an intrinsic mode of the RF field calculated by a separated code. The way of such simulation codes is not self-consistent completely. That is probably a major reason for the discrepancy between the experiments and the simulations. One of the other way for a self-consistent simulation codes is to use an FDTD (Finite Difference Time Domain) method. Since the FDTD method can take into account the microwave propagation including the space charge effect and the beam loading self-consistently, we have developed an FDTD code as 3-D Maxwell's equation solver and applied for a study of beam dynamics in a thermionic RF gun. The main purpose of simulaiton study is to obtain overall properties of the beam dynamics at the time. The goal of this simulation study of the thermionic RF gun is to understand correct characteristics of the thermionic RF gun for producing high brightness and short pulse beam.  
TPPE061 RF Design and Operating Performance of the BNL/AES 1.3 GHz Single Cell Superconducting RF Photocathode Electron Gun 3514
 
  • M.D. Cole
    AES, Medford, NY
  • I. Ben-Zvi, A. Burrill, H. Hahn, T. Rao, Y. Zhao
    BNL, Upton, Long Island, New York
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
 
  Over the past several years Advanced Energy Systems and BNL have been collaborating on the development and testing of a fully superconducting photocathode electron gun. Over the past year we have begun to realize significant results which have been published elsewhere.* This paper will review the RF design of the gun under test and present results of its performance under various operating conditions. Results for cavity quality factor will be presented for various operating temperatures and cavity field gradients. We will discuss various methods of determining the cavity fields and the extent of agreement between them. We will also discuss future plans for testing using this gun.

*Photoemission studies on BNL/AES all niobium, Superconducting RF injector, T. Rao, these proceedings.

 
TPPE062 Photoemission from Low Work Function Coated Metal Surfaces: A Comparison of Theory to Experiment
 
  • K. Jensen
    NRL, Washington, DC
  • D.W. Feldman, N.A. Moody, P.G. O'Shea
    IREAP, College Park, Maryland
 
  Funding: We gratefully acknowledge support provided by the Joint Technology Office and the Office of Naval Research.

The development of rugged and/or self rejuvenating photocathodes with high quantum efficiency (QE) using the longest wavelength drive laser is of paramount importance for RF photo-injectors for high power FELs and accelerators. We report on our program to develop advanced photocathodes and to develop and validate models of photoemission from coated metals to analyze experimental data,* provide emission models usable by beam simulation codes,** and project performance. The model accounts for the effects of laser heating, thermal evolution, surface conditions, laser parameters, and material characteristics, and predicts current distribution and QE. The photoemission and QE from metals and dispenser photocathodes is evaluated: the later introduces complications such as coverage non-uniformity and field enhancement. The performance of the models is compared to our experimental results for dispenser photocathodes and cesiated surfaces (e.g., tungsten, silver, etc.) in which the time-dependent models are shown to agree very well with experimental findings, but also to results in the literature. Extrapolations to performance regimes of interest shall be given.

*N. Moody et al., "Fabrication and Measurement of Low Workfunction Cesiated Dispenser Photocathodes" (this conference). **D.A. Dimitrov et al., "Development of Advanced Models for 3D Photocathode PIC Simulations" (this conference).

 
TPPE063 Improved Electron Yield and Spin-Polarization from III-V Photocathodes Via Bias Enhanced Carrier Drift 3603
 
  • G.A. Mulhollan, J.C.B. Bierman
    Saxet, Austin, Texas
  • A. Brachmann, J.E. Clendenin, E.G. Garwin, R.E. Kirby, D.-A.L. Luh, T.V.M. Maruyama
    SLAC, Menlo Park, California
  • R.X.P. Prepost
    UW-Madison/PD, Madison, Wisconsin
 
  Funding: Work at Saxet Surface Science, SLAC and the University of Wisconson is supported by the following U.S. DOE grants respectively: DE-FG02-04ER86231, DE-AC02-76SF00515 and DE-AC02-76ER00881.

Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile Preliminary measurements have been carried out on bulk GaAs. As expected, the yield change far from the bandgap is quite large. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. For a bias which enhances emission, the yield nearly doubles. For a bias which diminishes emission, the yield is approximately one half of the zero bias case. The size of the bias to cause an appreciable effect is rather small reflecting the low drift kinetic energy in the zero bias case.

 
TPPE064 Space-Charge Effects Near a Cathode 3629
 
  • V. Gorgadze
    UCB, Berkeley, California
  • J.S. Wurtele
    LBNL, Berkeley, California
 
  Funding: This work was supported by the Director, Office of Science of the U.S. DOE under Contract No. DE-AC03-76SF00098.

RF photocathode guns are excellent sources of high brightness electron bunches. In the limit of high-current short bunches the electron are complicated space-charge fields. To mitigate space charge effect downstream of the gun it is often desirable to produce electorn bunches with uniform distribution. Our goal is to understand to what extent the non-uniformity of the laser pulse intensity is responsible for a non-uniform electron distribution and to what extent this is due to the electron beam dynamics near to the cathode. We investigate these effects with particle-in-cell simulations and simple theory. These studies are focused on the regime where the peak current as well as the temporal current profile are influenced by the self-fields of the bunch. The simulation code XOOPIC has been employed. The critical current limitation for virtual cathode formation and current density profile at the exit of the injector have been found.

 
TPPE065 Calculating of Coupling Factor of Microwave Electron Gun 3656
 
  • X. Bian, H. Chen, S. Zheng
    TUB, Beijing
  • D. Li
    LBNL, Berkeley, California
 
  To design the coupler of a designing microwave electron gun, we use the "energy method" proposed by Derun Li, et al. The intrinsic Q of the electron gun cavity is very high: about 20000. The method calculates the intrinsic and external Q values of a cavity coupled to a waveguide using MAFIA code in time domain. The comparisons between simulation and experimental results are given for a set of different coupling iris apertures and height. The result shows that "energy method" works efficiently for high Q cavities.  
TPPE066 Geometry Optimization of DC/RF Photoelectron Gun 3679
 
  • P. Chen, R. Yi, D. Yu
    DULY Research Inc., Rancho Palos Verdes, California
 
  Funding: *Work supported by DOE SBIR Grant No. DE-FG02-03ER83878.

Pre-acceleration of photoelectrons in a pulsed, high voltage, short, dc gap and its subsequent injection into an rf gun is a promising method to improve electron beam emittance in rf accelerators. Simulation work has been performed in order to optimize the geometric shapes of a dc/rf gun and improve electron beam properties. Variations were made on cathode and anode shapes, dc gap distance, and inlet shape of the rf cavity. Simulations showed that significant improvement on the normalized emittance (< 1 mm-mrad), compared to a dc gun with flat cathode, could be obtained after the geometric shapes of the gun were optimized.