Experimental Study Of Plasma Filled Diode Operation Using Flashboard-Generated Plasmas

The impedance behavior of a 12-cm diameter plasma-filled, pinch-beam diode was studied on the NRL Gamble II generator. The generator was operated in negative polarity and the plasma was injected through the anode into the anode-cathode region. The plasma was generated on the surface of a capacitor-driven flashboard located downstream of the anode and was injected axially toward the diode. Results will be presented for the case where the plasma was injected through an annular slot in the anode in the vicinity of the anode-cathode gap, as well as, for the case where the plasma injection was limited by a 5-cm diameter hole on the anode at the center of the diode. By varying the relative timings between the capacitor bank firing and the machine pulse arrival, we were able to establish a window where the diode impedance started out at 0 Ω for a few tens of nanoseconds (<30 nsec) and then increased to the vacuum impedance. Attempts to increase conduction times beyond 30 nsec resulted in eventual impedances that were lower than the vacuum impedance. These results will be compared with those obtained by using in-situ hollow gas discharges. In addition, results will be presented from a limited number of experiments where the plasma filled diode was used with a plasma erosion opening switch upstream of the diode in order to study the coupling between the two.