Application of the NRL high-impedance radiography diode to a 2.3-MV generator

Summary form only given. A high-impedance, small spot size diode for flash radiography has been successfully tested on a 2.3-MV generator. The generator is an L-3 Communications, Pulse Sciences Division, Pulserad 43703B, the largest in a series of generators originally called Febetron. These generators are normally used with long-life, larger diameter anodes in a sealed glass envelope. Previous work with the 1-MV Pulserad 43710A generator has demonstrated that the sealed tube can be replaced with a stacked ring insulator and the large anode replaced with a small, 1-mm diameter anode in order to achieve a much smaller spot size for single shot use. Recently, the cathode design for this retrofitted diode has been improved for optimal performance. With only small changes, this vacuum stack and diode have been retrofitted to the 43703B 2.3-MV generator. Because of the higher voltage, extra rings were added to the insulator stack, and the outer conductor hardware was rearranged to provide a smooth surface. This new diode hardware has been successfully tested at the full, 35-kV charge voltage and preliminary results show the spot size reduced by about a factor of 5 to about 1 mm with only a modest decrease in dose. If a figure of merit for the radiography source is defined as the dose divided by the spot size squared, this retrofitted diode improves the figure of merit by more than a factor of 10. Future work will be to optimize the hardware design for field use and to optimize the performance of the diode with the aid of computer models.