Comparison of the implosion dynamics and radiation output of combined nested wire arrays with small diameter single arrays on the 1 MA COBRA generator

Abstract

Summary form only given. Experimental comparison of low-wire-number nested cylindrical wire arrays (inner and outer arrays of 6 mm and 13 mm diameter, respectively) composed of one or two materials (different in outer and inner arrays) and small (6 mm) diameter single cylindrical arrays are presented. Wire materials studied include Al alloys, stainless steel, and brass. Diagnostics include filtered PCDs, an EUV Si-diode, X-ray spectrometers, an optical streak camera, a time-gated EUV imaging pinhole camera, and laser probing. Small diameter stainless steel (or brass) wire arrays radiate comparable energy and more power in the first X-ray radiation burst than any nested arrays studied. In nested arrays of stainless steel (or brass) combined with Al, the stainless steel (or brass) wires reached the axis after the Al regardless of which array the heavier material was in. The delay was 15-25 ns for stainless steel and 5-10 ns for brass. Using different materials for nested arrays has a strong effect on the X-ray pulse shape as well. Some plasma bubbles that moved to the pinch axis were observed with the EUV time-gated camera. They appear from ruptured wires at first near the cathode and then spread from the cathode to the anode. Bubbles form first in the outer array and do not show correlation with bubbles from the inner array. Time-gated EUV pictures and the smooth rise of the EUV radiation during the time when the outer array plasma bubbles pass the inner array suggest that the outer array is imploding through the inner array without substantial interaction with the inner wires. The 1 keV radiation burst begins to rise within 10ns of this moment. The main X-ray pulse corresponds to the inner array imploding on the axis. Correlation between plasma bubble dynamics and radiation output was observed, yet it is unclear if the bubbles are transporting energy to the axis or if the X-ray bursts are a result of another process transporting energy to the axis.