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Genoni, T. C.

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THOBAB02 Commissioning the DARHT-II Scaled Accelerator Downstream Transport 2627
 
  • M. E. Schulze
  • E. O. Abeyta, P. Aragon, R. Archuleta, J. Barraza, D. Dalmas, C. Ekdahl, K. Esquibel, S. Eversole, R. J. Gallegos, J. Harrison, E. Jacquez, J. Johnson, P. S. Marroquin, B. T. McCuistian, N. Montoya, S. Nath, L. J. Rowton, R. D. Scarpetti, M. Schauer
    LANL, Los Alamos, New Mexico
  • R. Anaya, G. J. Caporaso, F. W. Chambers, Y.-J. Chen, S. Falabella, G. Guethlein, J. F. McCarrick, B. A. Raymond, R. A. Richardson, J. A. Watson, J. T. Weir
    LLNL, Livermore, California
  • H. Bender, W. Broste, C. Carlson, D. Frayer, D. Johnson, A. Tipton, C.-Y. Tom
    NSTec, Los Alamos, New Mexico
  • T. C. Genoni, T. P. Hughes, C. H. Thoma
    Voss Scientific, Albuquerque, New Mexico
  
  The DARHT-II accelerator will produce a 2-kA, 17-MeV beam in a 1600-ns pulse when completed this summer. After exiting the accelerator, the long pulse is sliced into four short pulses by a kicker and quadrupole septum and then transported for several meters to a tantalum target for conversion to bremsstrahlung for radiography. We describe tests of the kicker, septum, transport, and multi-pulse converter target using a short accelerator assembled from the first available refurbished cells, which are now capable of operating of operating at over 200 kV. This scaled accelerator was operated at ~ 8 Mev and ~1 kA, which provides a beam with approximately the same nu/gamma as the final 17-MeV, 2-kA beam, and therefore the same beam dynamics in the downstream transport. The results of beam measurements made during the commissioning of this scaled accelerator downstream transport are described.  
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THPAN082 Implementation of Spread Mass Model of Ion Hose Instability in Lamda 3408
 
  • Y. Tang
  • C. Ekdahl
    LANL, Los Alamos, New Mexico
  • T. C. Genoni, T. P. Hughes
    Voss Scientific, Albuquerque, New Mexico
  • M. E. Schulze
    SAIC, Los Alamos, New Mexico
  
  Funding: Work supported by Los Alamos National Laboratory.

The ion-hose instability sets limits on the allowable vacuum in the DARHT-2 linear induction accelerator (2kA, 18.6MeV, 2μs). Lamda is a transport code which advances the beam centroid and envelope in a linear induction accelerator from the injector to the final focus region. The code computes the effect of magnet misalignments, beam breakup instability, image-displacement instability, and gap voltage fluctuation on the beam. In this work, we have implemented the Spread Mass (SM) model of ion-hose instability into Lamda so that we can examine quickly the operating parameters for the experiments. Unlike the ordinary SM ion-hose code which assumes the uniform axial magnetic field, Lamda ion-hose calculation includes varying axial magnetic field, accelerating beam, gas pressure file, varying beam radius and elliptical beam. The benchmarks against a semi-analytical SM code and the particle-in-cell code Lsp, and a prediction of ion-hose instability for a 2.5MeV-1.4kA beam in the DARHT-2 are presented.

 
THPAN085 Two-Stream Instability Analysis For Propagating Charged Particle Beams With a Velocity Tilt 3417
 
  • D. Rose
  • R. C. Davidson, E. Startsev
    PPPL, Princeton, New Jersey
  • T. C. Genoni, D. R. Welch
    Voss Scientific, Albuquerque, New Mexico
  
  Funding: This research was supported by the U. S. DOE through Lawrence Berkeley National Laboratory, Princeton Plasma Physics Laboratory for the Heavy Ion Fusion Science-Virtual National Laboratory.

The linear growth of the two-stream instability for a charged particle beam that is longitudinally compressing as it propagates through a background plasma (due to an applied velocity tilt) is examined. Detailed, 1D particle-in-cell simulations are carried out to examine the growth of a wave packet produced by a small amplitude density perturbation in the background plasma. Recent analytic and numerical work by Startsev and Davidson [1] predicted reduced linear growth rates, which are indeed observed in the simulations. Here, small-signal asymptotic gain factors are determined in a semi-analytic analysis and compared with the simulation results in the appropriate limits. Nonlinear effects in the PIC simulations, including wave breaking and particle-trapping, are found to limit the linear growth phase of the instability for both compressing and non-compressing beams.

[1] Phys. Plasmas 13, 62108 (2006)