Density measurements in exploding wire-initiated plasmas using tungsten wires

Abstract

Calibrated density measurements have been obtained of the coronal plasmas around exploding 7.5–40 μm W wires carrying 15–120 kA per wire for 30–70 ns. X-ray radiographs of the exploding wire plasmas using 2.5–10 keV photons from a Mo wire X-pinch backlighter enabled measurements of areal densities of W ranging from 2×1017/cm2, equivalent to 0.03 μm of solid density W, to about 1019/cm2. The rapidly expanding (few mm/μs) coronal plasmas surrounding the slowly expanding (<1 mm/μs) residual wire cores have areal densities up to about 2×1018/cm2. Single 7.5 μm wires tested with 100 kA had as much as 90% of the initial wire material in the coronal plasma. Coronal plasma W number densities were estimated to be up to a few times 1018/cm3, while core W densities as low as a few times 1020/cm3 were observed. With linear arrays of four (eight) 7.5 μm wires carrying 30 kA (15 kA)/wire, up to 35% (25%) of the initial W wire material was in the plasma around and between the wires at 46–48 ns after the current started. Preheating the wires to drive off adsorbed gases and hydrocarbons increased the W mass in the coronal plasma and made it more uniform then when wires were not preheated.