• C. Ekdahl, E.O. Abeyta, P. Aragon, R.D. Archuleta, G.V. Cook, D. Dalmas, K. Esquibel, R.J. Gallegos, R.W. Garnett, J.F. Harrison, E.B. Jacquez, J.B. Johnson, B.T. McCuistian, N. Montoya, S. Nath, K. Nielsen, D. Oro, L.J. Rowton, M. Sanchez, R.D. Scarpetti, M. Schauer, G.J. Seitz, H.V. Smith, R. Temple
  LANL, Los Alamos, New Mexico
• H. Bender, W. Broste, C. Carlson, D. Frayer, D. Johnson, C.-Y. Tom, C.P. Trainham, J.T. Williams
  NSTec, Los Alamos, New Mexico
• T.C. Genoni, T.P. Hughes, C.H. Thoma
  Voss Scientific, Albuquerque, New Mexico
• B.A. Prichard, M.E. Schulze
  SAIC, Los Alamos, New Mexico

Funding: Work supported by USDOE under contract DE-AC52-06NA25396
The DARHT-II linear induction accelerator (LIA) accelerates a 2 kA electron beam to more than 17 MeV. The beam pulse has a greater than 1.5-microsecond flattop region over which the electron kinetic energy is constant to within 1%. The beam dynamics are diagnosed with 21 beam-position monitors located throughout the injector, accelerator, and after the accelerator exit, where we also have beam imaging diagnostics. I will discuss the tuning of the injector and accelerator, and I will present data for the resulting beam dynamics. Beam motion at the accelerator exit is undesirable for its application as a bremsstrahlung source for multi-pulse radiography of explosively driven hydrodynamic experiments. I will discuss the tuning procedures and other methods we use to minimize beam motion, and to suppress the beam-breakup (BBU) and ion-hose instabilities*.

*"Long-pulse beam stability experiments on the DARHT-II linear induction accelerator", Carl Ekdahl, et al., IEEE Trans. Plasma. Sci. Vol. 34, 2006, pp. 460-466.

• M.E. Schulze
  SAIC, Los Alamos, New Mexico
• E.O. Abeyta, R.D. Archuleta, J. Barraza, D. Dalmas, C. Ekdahl, W.L. Gregory, J.F. Harrison, E.B. Jacquez, J.B. Johnson, P.S. Marroquin, B.T. McCuistian, R.R. Mitchell, N. Montoya, S. Nath, K. Nielsen, R.M. Ortiz, L.J. Rowton, R.D. Scarpetti, M. Schauer, G.J. Seitz
  LANL, Los Alamos, New Mexico
• R. Anaya, G.J. Caporaso, F.W. Chambers, Y.-J. Chen, S. Falabella, G. Guethlein, 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, C.-Y. Tom
  NSTec, Los Alamos, New Mexico
• T.P. Hughes, C.H. Thoma
  Voss Scientific, Albuquerque, New Mexico

The DARHT-II accelerator produced a 2 kA, 17 MeV beam over a 1600 ns flattop. After exiting the accelerator, the long pulse is sliced into four short pulses by a kicker and quadrupole septum and then transported and focused on a target for conversion to bremsstrahlung for radiography. We describe the initial commissioning tests of the kicker, septum, transport, and multi-pulse converter target. The results of beam measurements made during the commissioning of the accelerator downstream transport are described. Beam optics simulations of the commissioning results are described.

Slides

• R. Sah, M. Alsharo'a, R.P. Johnson, M.L. Neubauer
  Muons, Inc, Batavia
• M. BastaniNejad, A.A. Elmustafa
  Old Dominion University, Norfolk, Virginia
• J.M. Byrd, D. Li
  LBNL, Berkeley, California
• D. Rose, C.H. Thoma, D.R. Welch
  Voss Scientific, Albuquerque, New Mexico
• G.M. Wang
  ODU, Norfolk, Virginia

The performance of many particle accelerators is limited by the maximum electric gradient that can be realized in rf cavities. Recent studies have shown that high gradients can be achieved quickly in 805 MHz cavities pressurized with dense hydrogen gas, because the gas can suppress, or essentially eliminate, dark currents and multipacting. In this project, two new test cells operating at 500 MHz and 1.3 GHz will be built and tested, and the high pressure technique will be used to suppress the vacuum effects of evacuated rf cavities, so that the role of metallic surfaces in rf cavity breakdown can be isolated and studied as a function of external magnetic field, frequency, and surface preparation. Previous studies have indicated that the breakdown probability is proportional to a high power of the surface electromagnetic field, in accordance with the Fowler-Nordheim description of electron emission from a cold cathode. The experiments will be compared with computer simulations of the rf breakdown process.