Plasma-filled diode for high dose-rate bremsstrahlung

A plasma-filled diode (PFD) can produce high dose-rate (>2 /spl times/ l0/sup 12/ rad/s) bremsstrahlung over small areas (100 cm/sup 2/) on the Saturn generator at Sandia. A PFD was developed for this purpose using the Gamble II generator at NRL. The maximum dose-rate was obtained with a conduction time of 40 ns, after which the voltage increased to 1.8 MV and the total current in the diode was 0.5 MA. The 3.6-Ohm maximum impedance is the same as for a hypothetical vacuum diode with an AK gap of 0.6 mm. The X-ray pulse width (FWHM) was 8 ns, much less than the typical 50 ns FWHM with a vacuum diode. This PFD was adapted to the higher-current (6-8 MA) Saturn generator by making a 10-cm diameter circular array of 6-12 isolated PFDs. Higher dose rates were obtained using fewer PFDs; about 1 /spl times/ 10/sup 12/ rad/s with the 12-PFD array, 2 /spl times/ l0/sup 12/ with 9 PFDs and 4 /spl times/ 10/sup 12/ with 6 PFDs. Analyses based on electrical and radiation diagnostics indicate that 40-75% of the electrical current produces radiation at the time of maximum dose rate. The X-ray pulse width was typically 12-15 ns, about half of the pulse width for standard (vacuum) bremsstrahlung diodes on Saturn. This system, with improvements in reproducibility at high dose rate, could provide a high dose-rate, small-area testing capability for Saturn.