Plasma-filled diode for high dose-rate bremsstrahlung

A plasma-filled diode (PFD) technique is described for producing high dose-rate bremsstrahlung over small areas. A PFD was developed for this purpose using the Gamble II generator. For maximum dose-rate conditions, the short-circuit phase duration was 40 ns, after which the voltage increased to 1.8 MV and the total current in the diode was 0.5 MA. The X-ray pulsewidth was 8 ns, much less than the typical 50 ns pulsewidth with a vacuum diode. This PFD was adapted to the higher-current Saturn generator at 6-8 MA by making a 10-cm diameter circular array of 6, 9, or 12 isolated PFDs. Higher dose rates were obtained using fewer PFDs; about 1 ×1012rad/s with the 12-PFD array, 2 ×1012 with nine PFDs and 4 ×1012 with 6 PFDs. Analyses based on electrical and radiation diagnostics indicate that 40%-77% of the electrical current produces radiation at the time of maximum dose rate. The X-ray pulsewidth was typically 13-16 ns, less than the pulsewidth for standard (vacuum) bremsstrahlung diodes on Saturn. This system, with improvements in reproducibility, could provide a high dose-rate, small-area bremsstrahlung capability for high current generators.