• R.R. Mitchell, B.A. Gardner, T. Ilg
  LANL, Los Alamos, New Mexico
• M. Leitner
  LBNL, Berkeley, California
• B.A. Prichard
  SAIC, Los Alamos, New Mexico

Funding: National Nuclear Security Administration of the US Department of Energy

The Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) at Los Alamos National Laboratory (LANL) consists of two linear induction accelerators oriented at right angles to each other. The DARHT First Axis has been successfully operated since 1999 and produces a 60 ns pulse with beam energy of 20 MeV and beam current of 1.9 kA. The DARHT Second Axis was successfully commissioned in May 2008 and produces a 1600 ns pulse with beam energy of 17.5 MeV and beam current of 2.1 kA. The Second Axis Injector uses a 16.5 cm diameter thermionic cathode with a 10 A/cm² required current density to emit electrons into the accelerator. During the early Second Axis commissioning activities in 2006, deficiencies in the DARHT Second Axis Injector were found that prevented the injector cathode from meeting the required 10 A/cm² current density. A comprehensive campaign was initiated to solve the injector cathode performance issues. This paper describes the deficiencies found and the solutions used to enable the DARHT Second Axis Injector to meet its requirements.

• 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
• 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, 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: This work was supported by the US National Nuclear Security Agency and the US Department of Energy under contract W-7405-ENG-36.

The DARHT-II linear induction accelerator (LIA) now accelerates 2-kA electron beams to more than 17 MeV. This LIA is unique in that the accelerated current pulse width is greater than 2 microseconds. This pulse has a flat-top region where the final electron kinetic energy varies by less than 1% for more than 1.5 microseconds. The long risetime of the 6-cell injector current pulse is 0.5 microsecond, which can be scraped off in a beam-head cleanup zone (BCUZ) before entering the 68-cell main accelerator. We discuss our experience with tuning this novel accelerator; and we will present data for the resulting beam transport and dynamics. We will also present beam stability data, and relate these to previous stability experiments at lower current and energy*.

* “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

Slides