Understanding Electrode Plasma Formation on Wires and Thin Foils Via Vacuum Ultraviolet Spectroscopy of Desorbed Surface Contaminants

Abstract

Power flow studies on the 30-MA, 100-ns Z facility at Sandia National Laborat ories (SNL) have shown that plasmas in the facility’s magnetically insulated transmission lines (MITLs) can result in a loss of current delivered to the load. 1 During the current pulse, thermal energy deposition into the electrodes (ohmic heating, charged particle bombardment, etc.) causes neutral surface contaminants layers (water, hydrogen, hydrocarbons, etc.) to desorb, ionize, and form plasmas in the anode-cathode (AK) gap. 2 Shrinking typical ele ctrode thicknesses (~1 cm) down to that of thin foils (5−200 µm) produces observable amounts of plasma on smaller pulsed power drivers (≤1 MA). 3 We suspect that as the electrode material bulk thickness decreases relative to the skin depth of the current pulse (50−100 µm for a 100−500-ns pulse in aluminum), the thermal energy delivered to the neutral surface contaminant layers increases, and thus more surface contaminants desorb from the current carrying surface.