Radiographic Paraxial Diode Investigations on RITS-6

Summary form only given. Presently, investigations of intense electron beam-driven diodes for flash x-ray radiography are being conducted on the upgraded RITS-6 accelerator, 9-12 MV, at Sandia National Laboratories. One of several diodes under investigation is the paraxial diode, which employs a gas-filled transport cell to focus the beam onto a high atomic number target to generate x-rays. Two key objectives are to produce a small spot size, < 5 mm, and high forward directed dose, ~600 Rads @ 1 m. Lsp simulations have shown that the primary limitation in spot size is due to the finite decay of the plasma return current which causes the beam focal location to shift axially during the timescale of the pulse, hence leading to an increased spot size. Replacing the gas with a preionized plasma has shown potential for stabilizing the beam focus by completely neutralizing the beam current. Plans for the incorporation of a novel plasma-filled version of the gas- filled paraxial are presented. Another outstanding issue for the paraxial diode on RITS-6 concerns the powerflow coupling from the magnetically insulated transmission line to the diode. Recent Lsp simulations have corroborated the existence of an excited mode, ~125 MHz, in the diode region which affects diode performance. Mitigation of this mode coupling is presented. Doses as well as time-integrated and time-resolved spot size measurements are reported. Initial spectroscopic data from the vacuum AK gap is also reported.