Measurement of mass density and charge state of precursor plasma in linear wire array experiments

Summary form only given. Precursor plasma has been observed in linear wire arrays that are positioned near a return current conductor. We report quantitative measurement of mass density and charge state of precursor plasma in linear Tungsten wire arrays (4 wires, 0.5 mm inter-wire gaps) affected by a global field. Experiments were done using Cornell´s XP pulser (450 kA peak current, 40 ns rise time). X-ray backlighting images of the wire array and the precursor plasma were taken at two different angles. With a W step wedge deposited on the X-ray filter, the mass density distributions of the precursor plasma in 3D were obtained. An interferometry system (3 channels, separated by 5 ns) using the second harmonic of a Nd:YAG laser (/spl lambda/=532 nm, 125 ps pulse width) was used as a diagnostic to measure the electron density of the precursor plasma. Combined with the mass distribution measured with the X-ray images, the charge state of the precursor plasma was determined.