Target studies for DARHT-II multi-pulse e-beam radiography

Summary form only given, as follows. In phase two of the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT-II), four electron beam pulses of variable pulse length strike an X-ray converter target to produce time-resolved X-ray images. An important requirement for the converter target is to minimize the hydrodynamic expansion of the converter material so that there is enough material to generate the required X-ray dose for all four pulses. It is also important to minimize the amount of backstreaming ions which can deteriorate the spot size. We will present several converter target configurations which include targets that are made of foamed tantalum, foamed Ta/sub 2/O/sub 5/, Ta-C composite material, and tantalum foils. Simulation results based on the radiation hydrodynamics code LASNEX and the Monte Carlo radiation transport code MCNP show that most of these targets can produce the required X-ray dose for all four pulses with tolerable X-ray spot size variation. The radiation output from some of these targets in fact exceeds the required dose by a factor of two and the X-ray outputs are robust in terms of spot size variation. Our calculations also show that a barrier foil may block the backstreaming ions for all four pulses.