Experimental Investigation of Beam Optics Issues at the Bremsstrahlung Converters for Radiographic Applications

As part of the Dual Axis Radiographic Hydrodynamic Test Facility II (DARHT II) and Advanced Hydrotest Facility (AHF) programs, we have began investigation of the possible adverse effects of (1) backstreaming ion emission from the Bremsstrahlung converter target and (2) the interaction of the resultant plasma with the electron beam during subsequent pulses. These effects would primarily manifest themselves in the static focusing system as a rapidly varying x-ray spot. To study these effects, we are conducting beam-target interaction experiments on the ETA-II accelerator (a 6.0 MeV, 2.5 kA, 70 ns FWHM pulsed, electron accelerator). From these experiments and the multiple diagnostics we have implemented, we are able to determine spot dynamics and characterize the resultant plasma for various configurations. Our data to date shows the first effect to be minimal. We report on the details of our experiments and our preliminary experiments to study the second effect.