X-RAY RESULTS FROM A MODIFIED NOZZLE AND DOUBLE GAS PUFF-Z PINCH

The nozzle and the anode of the UCI (University of California, Irvine) z-pinch facility were modified to study the influence of the anode-cathode geometrical structure on the stability of the pinch and the x-ray yield of the pinch. The anode was modified from a honey-comb to a hollow cylinder with a 4-cm diameter and a approximately 3.5-mm wall thickness, placed 2 cm below the cathode. The cavity in the center of the cathode was enlarged from 6-mm diameter to 36 mm. The design of the cathode and the anode showed a marked improvement of the pinch stability over the previous design. Both zirconium and carbon-carbon nozzle were used for the Kr and Ne z pinches. After a few tens of shots the Zr nozzle was melted at the edge and the pinch degraded, while the carbon-carbon nozzle did not sustain any damage for more than 300 shots. Some shots showed the di/dt at the implosion is approximately 5 times higher than the di/dt at the beginning of the discharge, this has never been obtained at UCI before. This ratio of the initial di/dt to pinch di/dt is a measure of the pinch quality. By serendipity it was found that double gas puff z pinch increased the hard x-ray (> 1 keV) output by about an order of magnitude. The nozzle was then modified to allow double puff operation. A 3.4-mm-diam hole was opened at the center of the nozzle and a plunger was inserted from the top to control the mass of the gas entering the hole. The diagnostics include di/dt coil, soft, and hard x-ray diodes. Soft and hard x-ray emission are both enhanced by the double gas puff z pinch.