Ablation Loss Studies for Capillary-Sustained Plasmas

Abstract : The most common discharge geometry used for efficiently generating plasma from stored electrical energy for gun ignition utilizes a capillary tube to contain, direct, and sustain the discharge. The plasma gas composition is determined by the air in the tube before discharge begins and by materials removed from the capillary tube wall, electrodes, and exploding wire used to start the event. The conductivity of the plasma in the capillary affects the discharge and the conversion of energy. The optimized materials, properties, and geometries for these components have not been identified. A reasonable first step in understanding the capillary tube dynamics would be to model and experimentally quantify parameters of interest. In the present work, a series of parametric experiments has been conducted utilizing polyethylene and Teflon capillary-sustained plasmas in which the mass ablation for the capillary tube is measured. The capillary geometry, exploding wire geometry, and material and energy input to the plasma have been varied to provide insight into their respective effects on the ablation. A systematic study of the efficiency of stored energy deposited into the plasma will be made with capillary wall material, capillary diameter and length, and the effects of exploding wires as variables. Observations and their implication on validation of capillary tube models are discussed.