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Molvik, A. W.

Paper Title Page
MOOBC02 Experiments in Warm Dense Matter using an Ion Beam Driver 140
  • F. M. Bieniosek, M. Leitner, B. G. Logan, R. More, P. N. Ni, P. K. Roy
    LBNL, Berkeley, California
  • J. J. Barnard, M. Kireeff Covo, A. W. Molvik
    LLNL, Livermore, California
  • L. Grisham
    PPPL, Princeton, New Jersey
  • H. Yoneda
    University of electro-communications, Tokyo
  Funding: Work performed under the auspices of the U. S. Dept. of Energy by LBNL, LLNL, and PPPL under Contracts No. W-7405-Eng-48, DE-AC02-05CH11231, and DE-AC02-76CH3073.

We describe near term heavy-ion beam-driven warm dense matter (WDM) experiments. Initial experiments are at low beam velocity, below the Bragg peak, increasing toward the Bragg peak in subsequent versions of the accelerator. The WDM conditions are envisioned to be achieved by combined longitudinal and transverse neutralized drift compression to provide a hot spot on the target with a beam spot size of about 1 mm, and pulse length about 1-2 ns. The range of the beams in solid matter targets is about 1 micron, which can be lengthened by using porous targets at reduced density. Initial candidate experiments include an experiment to study transient darkening in the WDM regime; and a thin target dE/dx experiment to study beam energy and charge state distribution in a heated target. Further experiments will explore target temperature and other properties such as electrical conductivity to investigate phase transitions and the critical point.

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TUXAB01 Absolute Measurement of Electron Cloud Density 754
  • M. Kireeff Covo, R. H. Cohen, A. Friedman, A. W. Molvik
    LLNL, Livermore, California
  • D. Baca, F. M. Bieniosek, B. G. Logan, P. A. Seidl, J.-L. Vay
    LBNL, Berkeley, California
  • J. L. Vujic
    UCB, Berkeley, California
  Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U. S. Department of Energy, LLNL and LBNL, under contracts No. W-7405-Eng-48 and DE-AC02-05CH11231.

Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 us duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.*

* M. Kireeff Covo, A. W. Molvik, A. Friedman, J.-L. Vay, P. A. Seidl, G. Logan, D. Baca, and J. L. Vujic, Phys. Rev. Lett. 97, 054801 (2006).

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TUXAB03 Self-consistent 3D Modeling of Electron Cloud Dynamics and Beam Response 764
  • M. A. Furman, C. M. Celata, M. Kireeff Covo, K. G. Sonnad, J.-L. Vay, M. Venturini
    LBNL, Berkeley, California
  • R. H. Cohen, A. Friedman, D. P. Grote, A. W. Molvik
    LLNL, Livermore, California
  • P. Stoltz
    Tech-X, Boulder, Colorado
  Funding: Work supported by the U. S. DOE under Contracts DE-AC02-05CH11231 and W-7405-Eng-48, and by the US-LHC Accelerator Research Project (LARP).

We present recent advances in the modeling of beam-electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation.

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THPAS050 Simulating Electron Effects in Heavy-Ion Accelerators with Solenoid Focusing 3603
  • W. M. Sharp, R. H. Cohen, A. Friedman, D. P. Grote, A. W. Molvik
    LLNL, Livermore, California
  • J. E. Coleman, P. K. Roy, P. A. Seidl, J.-L. Vay
    LBNL, Berkeley, California
  • I. Haber
    UMD, College Park, Maryland
  Funding: This work was performed under the auspices of US DOE by the University of California Lawrence Livermore and Lawrence Berkeley National Laboratories under contracts W-7405-Eng-48 and DE-AC03-76SF00098.

Contamination from electrons is a concern for solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons, produced directly by beam ions hitting lattice elements or indirectly by ionization of desorbed neutral gas, can potentially alter the beam dynamics, leading to a time-varying focal spot, increased emittance, halo, and possibly electron-ion instabilities. The electrostatic particle-in-cell code WARP is used to simulate electron-cloud studies on the solenoid-transport experiment (STX) at Lawrence Berkeley National Laboratory. We present self-consistent simulations of several STX configurations to show the evolution of the electron and ion-beam distributions first in idealized 2-D solenoid fields and then in the 3-D field values obtained from probes. Comparisons are made with experimental data, and several techniques to mitigate electron effects are demonstrated numerically.

THPAS006 A Solenoid Final Focusing System with Plasma Neutralization for Target Heating Experiments 3519
  • P. K. Roy, F. M. Bieniosek, J. E. Coleman, J.-Y. Jung, M. Leitner, B. G. Logan, P. A. Seidl, W. L. Waldron
    LBNL, Berkeley, California
  • J. J. Barnard, A. W. Molvik
    LLNL, Livermore, California
  • R. C. Davidson, P. Efthimion, E. P. Gilson, A. B. Sefkow
    PPPL, Princeton, New Jersey
  • J. A. Duersch, D. Ogata
    UCB, Berkeley, California
  • D. R. Welch
    Voss Scientific, Albuquerque, New Mexico
  Intense bunches of low-energy heavy ions have been suggested as means to heat targets to the warm dense matter regime (0.1 to 10 eV). In order to achieve the required intensity on target (~1 eV heating), a beam spot radius of approximately 0.5 mm, and pulse duration of 2 ns is required with an energy deposition of approximately 1 J/cm2. This translates to a peak beam current of 8A for ~0.4 MeV K+ ions. To increase the beam intensity on target, a plasma-filled high-field solenoid is being studied as a means to reduce the beam spot size from several mm to the sub-mm range. We are building a prototype experiment to demonstrate the required beam dynamics. The magnetic field of the pulsed solenoid is 5 to 8 T. Challenges include suitable injection of the plasma into the solenoid so that the plasma density near the focus is sufficiently high to maintain space-charge neutralization of the ion beam pulse. Initial experimental results for a peak current of ~1A will be presented.

This work was supported by the Office of Fusion Energy Sciences, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231, W-7405-Eng-48, DE-AC02-76CH3073 for HIFS-VNL.