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Sefkow, A. B.

Paper Title Page
WEZC02 Extreme Compression of Heavy Ion Beam Pulses: Experiments and Modeling 2030
 
  • A. B. Sefkow, R. C. Davidson, P. Efthimion, E. P. Gilson, I. Kaganovich
    PPPL, Princeton, New Jersey
  • J. J. Barnard
    LLNL, Livermore, California
  • J. E. Coleman, P. K. Roy, P. A. Seidl
    LBNL, Berkeley, California
  • D. R. Welch
    Voss Scientific, Albuquerque, New Mexico
 
  Funding: Research supported by the U. S. Department of Energy.

Intense heavy ion beam pulses need to be compressed in both the transverse and longitudinal directions for warm dense matter and heavy ion fusion applications. Previous experiments and simulations utilized a drift region filled with high-density plasma in order to neutralize the space-charge and current of a 300 keV K+ beam, and achieved transverse and longitudinal focusing separately to a radius < 2 mm and pulse width < 5 ns, respectively. To achieve simultaneous beam compression, a strong solenoid is employed near the end of the drift region in order to transversely focus the beam to the longitudinal focal plane. Simulations of near-term experiments predict that the ion beam can be focused to a sub-mm spot size coincident with the longitudinal focal plane, reaching a peak beam density in the range 1012 - 1013 cm-3, provided that the plasma density is large enough for adequate neutralization. Optimizing the compression under the appropriate experimental constraints offers the potential of delivering higher intensity per unit length of accelerator to the target, thereby allowing more compact and cost-effective accelerators and transport lines to be used as ion beam drivers.

 
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THPAN086 End-to-end Simulations of an Accelerator for Heavy Ion Beam Bunching 3420
 
  • D. R. Welch, D. Rose
    Voss Scientific, Albuquerque, New Mexico
  • J. E. Coleman, E. Henestroza, P. K. Roy, P. A. Seidl
    LBNL, Berkeley, California
  • E. P. Gilson, A. B. Sefkow
    PPPL, Princeton, New Jersey
 
  Funding: This research was supported by the U. S. Department of Energy through Princeton Plasma Physics Laboratory and Lawrence Berkeley National Laboratory for the HIFS-VNL.

Longitudinal bunching factors in excess of 70 of a 300-keV, 27-mA K+ ion beam have been demonstrated in the Neutralized Drift Compression Experiment in rough agreement with LSP particle-in-cell end-to-end simulations. These simulations include both the experimental diode voltage and induction bunching module voltage waveforms in order to specify the initial beam longitudinal phase space critical to longitudinal compression. To maximize simultaneous longitudinal and transverse compression, we designed a solenoidal focusing system that compensated for the impact of the applied velocity tilt on the transverse phase space of the beam. Here, pre-formed plasma provides beam neutralization in the last one meter drift region where the beam perveance becomes large. Integrated LSP simulations, that include detailed modeling of the diode, magnetic transport, induction bunching module, plasma neutralized transport, were critical to understanding the interplay between the various accelerator components. Here, we compare simulation results with the experiment and discuss the contributions to longitudinal and transverse emittance that limit compression.

 
THPAS004 Bunching and Focusing of an Intense Ion Beam for Target Heating Experiments 3516
 
  • J. E. Coleman, P. K. Roy, P. A. Seidl
    LBNL, Berkeley, California
  • E. P. Gilson, A. B. Sefkow
    PPPL, Princeton, New Jersey
  • D. Ogata
    UCB, Berkeley, California
  • D. R. Welch
    Voss Scientific, Albuquerque, New Mexico
 
  Funding: This work was supported by the U. S. D. O.E. under DE-AC02-05H11231 and DE-AC02-76CH3073 for HIFS-VNL

Future warm dense matter experiments with space-charge dominated ion beams require simultaneous longitudinal bunching and transverse focusing. The challenge is to longitudinally bunch the beam two orders of magnitude to a pulse length shorter than the target disassembly time and focus the beam transversely to a sub-mm focal spot. An experiment to simultaneously focus a singly charged potassium ion beam has been carried out at LBNL. The space charge of the beam must be neutralized so only emittance limits the simultaneous focusing. An induction bunching module provides a head-to-tail velocity ramp upstream of a plasma filled drift section. Tuning the initial beam envelope to compensate for the defocusing of the bunching module enables simultaneous focusing. A comparison of experimental and calculated results are presented, including the transverse distribution and the longitudinal phase-space of the beam.

 
THPAS083 Charge and Current Neutralization of an Ion Beam Pulse by Background Plasma in Presence of Applied Magnetic Field and Gas Ionization 3675
 
  • J. S. Pennington
    USC, Los Angeles, California
  • R. C. Davidson, I. Kaganovich, A. B. Sefkow, E. Startsev
    PPPL, Princeton, New Jersey
 
  Funding: *Research supported by the U. S. Department of Energy under the auspices of the Heavy Ion Fusion Science Virtual National Laboratory.

Background plasma can be used as a convenient tool for manipulating intense charge particle beams, for example, for ballistic focusing and steering, because the plasma can effectively reduce the space-charge potential and self-magnetic field of the beam pulse. We previously developed a reduced analytical model of beam charge and current neutralization for an ion beam pulse propagating in a cold background plasma. The reduced-fluid description provides an important benchmark for numerical codes and yields useful scaling relations for different beam and plasma parameters. This model has been extended to include the additional effects of a solenoidal magnetic field and gas ionization. Analytical studies show that a sufficiently large solenoidal magnetic field can increase the degree of current neutralization of the ion beam pulse. The linear system of equations has been solved analytically in Fourier space. For a strong enough applied magnetic field, poles emerge in Fourier space. These poles are an indication that whistler waves and lower hybrid waves are excited by the beam pulse.

 
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.