Density and temperature distributions in the plasma expanding from an exploded wire in vacuum

The plasma expansion from an exploded wire with characteristic times of energy deposition in the wire of tens of microseconds was studied. The probe method was used to measure the plasma temperature and plasma density distributions. Tungsten wires 25, 50, 75, and 125 μm in diameter and a copper wire 100 μm in diameter were used. The waveforms of discharge voltage Ud, discharge current Id, and floating potential showed that Ud was close to a constant, while Id decreased, indicating that the wire resistance increased until plasma appeared. Immediately after the appearance of plasma, Id was observed to peak, while the voltage decreased stepwise from ∼110 to about 70 V. A relatively high electron temperature (about 12 eV) was observed in the expanding plasma even at r=2 cm from the wire axis. The plasma density was a maximum of 2× 1013 cm-3 at r=2 cm, and it decreased with increasing r. For r<2 cm, unusual electrical parameters were observed, indicating the probe activity and a significantly increased plasma density in the region close to the wire core.