Preliminary investigation into electrical properties of metal-vapor layers in electrothermal plasma sources

Abstract

Summary form only given, as follows. Plasma capillary discharges are widely used in electric launchers applications to either inject a plasma into a propellant in electrothermal chemical devices, or as a pre-injector in electromagnetic launchers. Plasma formation, parameters and flow govern the processes within the launching device. When forming a plasma using a metal liner inside of the capillary, or using a fuse, it is necessary to understand the role of plasma conductivity and current distribution to get a complete picture of the discharge. Accurate description of plasma conductivity would greatly help in understanding the role of discharge current, which is an important term in the conservation of energy equation. Although it is usually assumed that plasma conductivity is that of the plasma bulk inside of the capillary, but it Is of particular interest to understand the role of the metal-vapor layer on the overall behavior of plasma conductivity. Experiments at N.C. State University on the SIRENS electrothermal plasma device employ the use of metal liners inside of the capillary discharge. Because of the diminutive size of the source section of SIRENS, it is hard to implement diagnostic tools to directly measure parameters of the metal-vapor layer. Therefore, it is necessary to employ a model to describe this region. Following Powell, Thornhill and Batteh's (1997) model of electrical conduction of exploding or ablating solid conductors, a 3-zone model has been developed which relates the conductivity to the wall and plasma temperature. Also, a steady-state model for the current distributions within the three regions, i.e., the plasma, metal vapor layer, and the solid liner has been developed.