Observation of a core in an exploded lithium wire plasma by reflection of laser light

Abstract

A thin lithium wire which was extruded and exploded in vacuo was probed with a Q‐switched ruby laser. Strong reflections of the ruby laser light were observed from a ``core'' in the plasma when the pressure was greater than 5 × 10<sup>−4</sup> Torr. Changes in the plasma and discharge properties near this pressure suggested the possibility of a core of unvaporized wire due to current shunting through the surrounding air. The presence of this core was unexpected because of the relatively large discharge current and small wire diameter. When the pressure was below 5 × 10<sup>−4</sup> Torr a ``core'' was never observed and there was no evidence of current shunting.