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Baca, D.

Paper Title Page
WPAT055 Enhancements for the 1 MW High Voltage Converter Modulator Systems at the SNS 3313
  • D.E. Anderson, J. Hicks, D. E. Hurst, E.R. Tapp, M. Wezensky
    ORNL, Oak Ridge, Tennessee
  • D. Baca, W. Reass
    LANL, Los Alamos, New Mexico
  • V.V. Peplov
    RAS/INR, Moscow
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

The first-generation high frequency switching megawatt-class high voltage converter modulators (HVCM) developed by Los Alamos National Laboratory for the Spallation Neutron Source at Oak Ridge National Laboratory have been installed and are now operational. Each unit is capable of delivering pulses up to 11 MW peak, 1 MW average power at voltages up to 140 kV to drive klystron(s) rated up to 5 MW. To date, three variations of the basic design have been installed, each optimized to deliver power to a specific klystron load configuration. Design improvements, with the primary intention of improving system reliability and availability, have been under development since the initial installation of the HVCM units. This paper will examine HVCM reliability studies, reliability operational data, and modifications and improvements performed to increase the overall system availability. We will also discuss system enhancements aimed at improving the ease of operation and providing for additional equipment protection features.

ROPB002 Experiments Studying Desorbed Gas and Electron Clouds in Ion Accelerators 194
  • A.W. Molvik, J.J. Barnard, R.H. Cohen, A. Friedman, M. Kireeff Covo, S.M. Lund
    LLNL, Livermore, California
  • D. Baca, F.M. Bieniosek, C.M. Celata, P.A. Seidl, J.-L. Vay, W. Waldron
    LBNL, Berkeley, California
  • J.L. Vujic
    UCB, Berkeley, California
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL under contract No. W-7405-Eng-48, and by LBNL under Contract DE-AC03-76F00098.

Electron clouds and gas pressure rise limit the performance of many major accelerator rings. We are studying these issues experimentally with ~1 MeV heavy-ion beams, coordinated with significant efforts in self-consistent simulation and theory.* The experiments use multiple diagnostics, within and between quadrupole magnets, to measure the sources and accumulation of electrons and gas. In support of these studies, we have measured gas desorption and electron emission coefficients for potassium ions impinging on stainless steel targets at angles near grazing incidence.** Our goal is to measure the electron particle balance for each source – ionization of gas, emission from beam tubes, and emission from an end wall – determine the electron effects on the ion beam and apply the increased understanding to mitigation.

*J-L. Vay, Invited paper, session TICP; R. H. Cohen et al., PRST-AB 7, 124201 (2004). **M. Kireeff Covo, this conference; A. W. Molvik et al., PRST-AB 7, 093202 (2004).

FPAE071 Initial Results on Neutralized Drift Compression Experiments (NDCX-IA) for High Intensity Ion Beam 3856
  • P.K. Roy, A. Anders, D. Baca, F.M. Bieniosek, J.E. Coleman, S. Eylon, W.G. Greenway, E. Henestroza, M. Leitner, B. G. Logan, D. Shuman, D.L. Vanecek, W. Waldron, S. Yu
    LBNL, Berkeley, California
  • R.C. Davidson, P. Efthimion, E.P. Gilson, I. Kaganovich, A.B. Sefkow
    PPPL, Princeton, New Jersey
  • D. Rose, C.H. Thoma, D.R. Welch
    ATK-MR, Albuquerque, New Mexico
  • W.M. Sharp
    LLNL, Livermore, California
  Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

Ion beam neutralization and compression experiments are designed to determine the feasibility of using compressed high intensity ion beams for high energy density physics (HEDP) experiments and for inertial fusion power. To quantitatively ascertain the various mechanisms and methods for beam compression, the Neutralized Drift Compression Experiment (NDCX) facility is being constructed at Lawrence Berkeley National Laboratory (LBNL). In the first compression experiment, a 260 KeV, 25 mA, K+ ion beam of centimeters size is radially compressed to a mm size spot by neutralization in a meter-long plasma column and beam peak current is longitudinally compressed by an induction velocity tilt core. Instrumentation, preliminary results of the experiments, and practical limits of compression are presented. These include parameters such as emittance, degree of neutralization, velocity tilt time profile, and accuracy of measurements (fast and spatially high resolution diagnostic) are discussed.

FPAP015 Electron and Gas Effects on Intense, Space-Charge Dominated Ion Beams in Magnetic Quadrupoles: Comparison of Experiments and Simulations
  • P.A. Seidl, D. Baca, F.M. Bieniosek, J.-L. Vay
    LBNL, Berkeley, California
  • R.H. Cohen, A. Friedman, D.P. Grote, M. Kireeff Covo, S.M. Lund, A.W. Molvik
    LLNL, Livermore, California
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL and LBNL under contracts W-7405-Eng-48, and DE-AC03-76F00098.

Accelerators for inertial fusion energy, high-energy density physics and other high intensity applications have an economic incentive to minimize the clearance between the beam edge and the aperture wall. This increases the risk from electron clouds and gas desorbed from walls. Using the High Current Experiment at LBNL, we have measured the beam (0.18 A, 1 MeV K+ ) distribution upstream and downstream of a short lattice of magnetic quadrupoles where the 2·rms beam size is =50% of the quadrupole aperture, and the generalized perveance is 10-3. Between magnets, the transverse beam distribution is also imaged. The beam potential is 1-2 kV, large enough to trap electrons produced by, for example, K+ - gas collisions. Gas and electron effects are intentionally induced by varying gas pressure and the bias of e- controlling electrodes.* The measurements are compared to WARP PIC simulations that include the self-consistent tracking of electrons and ions.**

*A. W. Molvik et al., this conference. **J-L Vay et al., this conference.

FPAP033 Beam Energy Scaling of Ion-Induced Electron Yield from K+ Ions Impact on Stainless Steel Surfaces 2287
  • M. Kireeff Covo, J.J. Barnard, R.H. Cohen, A. Friedman, D.P. Grote, S.M. Lund, A.W. Molvik, G.A. Westenskow
    LLNL, Livermore, California
  • D. Baca, F.M. Bieniosek, C.M. Celata, J.W. Kwan, P.A. Seidl, J.-L. Vay
    LBNL, Berkeley, California
  • J.L. Vujic
    UCB, Berkeley, California
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL under contract No. W-7405-Eng-48, and by LBNL under Contract DE-AC03-76F00098.

The cost of accelerators for heavy-ion inertial fusion energy (HIF) can be reduced by using the smallest possible clearance between the beam and the wall from the beamline. This increases beam loss to the walls, generating ion-induced electrons that could be trapped by beam space charge potential into an "electron cloud," which can cause degradation or loss of the ion beam. In order to understand the physical mechanism of production of ion-induced electrons we have measured impact of K+ ions with energies up to 400 KeV on stainless steel surfaces near grazing incidence, using the ion source test stand (STS-500) at LLNL. The electron yield will be discussed and compared with experimental measurements from 1 MeV K+ ions in the High-Current Experiment at LBNL.*

*A.W. Molvik et al., PRST-AB 7, 093202 (2004).