Design and performance of the Marx generator for the DARHT second axis electron injector

The injector for the second axis of the dual-axis radiographic hydrotest facility (DARHT II) is now undergoing commissioning tests at Los Alamos national laboratory. A Marx generator develops a 3.2 MV, 2 /spl mu/s pulse that is applied to the diode through a high voltage (or Marx) dome, current stalk and high voltage insulator column. The 2 kA electron beam source is a 165-mm-diameter thermionic dispenser cathode operating near 120 kV/cm. The extracted beam enters a series of eight pulsed power-driven injector induction cells that accelerate the beam to approximately 4.5 MeV. The beam then passes through a beamhead clean-up zone (BCUZ) to "scrape off" the off-energy portion of the beam (the beam leading edge and, to a lesser extent, the beam trailing edge). A crowbar switch fired at the end of 2 /spl mu/s produces a short fall time. This paper focuses on the electrical and mechanical design and testing of the Marx generator. The Marx consists of 88 stages, each half stage of which is a +/- 50 kV type EPFN. The Marx was tested for over 8000 shots before shipment to Los Alamos and demonstrated 6 ns jitter and good reliability with only 8 prefires out of 5000 shots. At the end of December 2002, nearly 800 shots have been fired in the process of commissioning the DARHT machine. The results of both series of these tests are given in this paper.