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

Power-flow studies on the 30-MA, 100-ns Z facility at Sandia National Labs have shown that plasmas in the facility's magnetically insulated transmission lines can result in a loss of current to the load. ¹ During the current pulse, electrode heating causes neutral surface contaminants (water, hydrogen, hydrocarbons, etc.) to desorb, ionize, and form plasmas in the anode-cathode gap. ² Shrinking typical electrode thicknesses (~1 cm) to thin foils (5–200 μm) produces observable amounts of plasma on smaller pulsed power drivers <1 MA).3 We suspect that as electrode material bulk thickness decreases relative to the skin depth (50–100 μm for a 100-500-ns pulse in aluminum), the thermal energy delivered to the neutral surface contaminants increases, and thus desorb faster from the current carrying surface.