Operation of an extraction, applied-B diode using an externally-driven, metallic foil anode plasma source

Summary form only given. We are developing an extraction, applied-B ion diode, on the Gamble II generator at NRL, for ion-beam-transport research in support of the SNL light-ion ICF program. An ion beam with a voltage above 1 MV and a proton current of 150-200 kA is required for transport experiments. At present we are using hardware which allows a maximum anode area of /spl sim/60 cm/sup 2/. These parameters result in enhancement factors 2-3 times greater than those in similar experiments at Cornell, SNL, and KfK. In addition, the early, high-impedance phase of the diode must be minimized to prevent insulator flashover. Transport experiments with beam focusing also preclude ion beam angular momentum. A version of the EMFAP source, developed at Cornell and improved at KfK is used to provide prompt turn-on of the ion current. This source comprises a thin metallic foil on an insulating substrate. Driving current through this foil results in rapid heating, gas desorption and breakdown and thus a uniform plasma conformal to the anode surface. An external pulser is used to drive current through the foil. The applied magnetic field is calculated using the ATHETA code. Recently, these calculations have been refined by direct measurement of rA/sub 8/. To date we have obtained ion beams with rapid turn-on, high currents and current densities (350 kA at 6 kA/cm/sup 2/), high ion efficiencies (80%).