Plasma-filled rod-pinch diode experiment on Gamble II

A plasma-filled rod-pinch diode, fielded on the NRL Gamble II generator, may represent a breakthrough in concentrating electron-beam energy into a small volume. Injected plasma connects the grounded cathode to the concentric tungsten rod anode. After a short-circuit phase lasting 10-30 ns, the impedance increases and a large fraction of the electron-beam energy is deposited on the tip of the rod, producing a small, intense X-ray source. As the injected plasma density increases, the current and voltage (at the time of maximum radiation) range from 260 kA and 1.8 MV to 770 kA and 0.45 MV. These parameters imply effective anode-cathode gaps of 130 to 7 /spl mu/m, far smaller than can be achieved with metal electrodes without premature shorting. The physics of the plasma-filled rod-pinch diode differs from its vacuum analog. Current can be convected to the rod tip by plasma translation instead of electron-beam propagation. When plasma is pushed beyond the tip of the rod, a gap can form there by erosion. The high current and voltage, combined with the small anode diameter, may produce record electron-beam power densities (75 TW/cm/sup 2/) and high-energy-density plasma conditions at the rod tip. Potential applications include improved radiography sources, X-ray/matter interaction studies, and high-energy-density plasma generation.