Negative polarity plasma filled rod pinch: initial experiments on GAMBLE II

Summary form only given. Initial exploratory experiments on a Negative Polarity Plasma Filled Rod Pinch (NPPFRP) have been made on GAMBLE II. The Rod Pinch (RP) and the Plasma Filled Rod Pinch (PFRP) diodes, in the conventional positive polarity, have already been studied. Although proven useful as small spot size radiography sources, it is believed that the RP and the PFRP diodes, when driven with voltages greater than 2 MV, produce a large fraction of their bremsstrahlung X-ray yield in the direction of the generator, hence making this fraction of the radiation useless. It is the intention of the NPPFRP to increase and optimize the X-ray yield in the forward direction, away from the generator, so that these X-rays become useful for radiography purposes. In our experiment, typical diode geometry consisted of a 1 mm diameter 4.1 cm long tungsten rod anode backed with a 6 mm thick carbon square sheet at the base and a 1 cm diameter tube cathode with a plasma gun in the center of the tube set at 1 cm from the cathode tube edge. The anode-cathode gap was set at 1 cm (edge of tube to rod tip). Diagnostics fielded are TLD dosimeters, film loaded pinhole cameras, and scintillator-photodiode X-ray detectors. With this configuration, the X-ray yield was 8.5 rad (CaF/sub 2/) at 1 m in the forward direction and 5.0 rad (CaF/sub 2/) at 1 m at 90 degrees. Peak X-rays occur at a diode voltage of 1.25 MV and 250 kA. It is observed that the X-ray emission is from a concentrated source at the tip of the anode rod with additional radiation from the carbon sheet. There is no evidence of any radiation emitted along the length of the rod. The radiation from the tip and the base of the anode is not coincident in time; the radiation from the tip occurs first.