Rod-pinch electron beam diodes as X-ray radiography sources

This paper reports on recent NRL Gamble II experiments with rod-pinch diodes which duplicate and extend previous results. These diodes utilize a thin annular cathode surrounding a small diameter anode rod extending through and beyond the plane of the cathode. Up to seven rods were simultaneously pulsed with each rod displaying well behaved electrical characteristics (0.8-1.5 MV at impedances of 15 to 30 ohms). Time and spatially resolved X-ray Pin diode detectors demonstrated efficient current (>50%) propagation along each rod. The 50 rads Si that was measured 30 cm from each carbon rod (0.16 cm radius) with Ta cone tips at 1.5 MV corresponds to 10-1000 times the dose of other point radiography sources. While previous rod-pinch experiments were performed with solid rods, a new high-velocity, high-efficiency propagation mode was demonstrated using a hollow cylinder with a 6-μm Al wall and a carbon end plug. It is speculated that the propagation was via electron reflexing through the thin anode rod without the need for anode ion production. Also, when no end plug was used, the electron beam appeared to reflex along the entire length of the rod until it lost its energy