The Impact of Cathode Diameter on Radial Foil Explosions

Radial foil configurations prove to be a very simple experimental setup to study high-energy-density plasmas. A thin metallic foil lies flat over a stretcher which is connected to the anode of a pulsed-power generator. The cathode contacts the foil at its geometrical center using a hollow stainless steel pin. Force densities should increase dramatically as the pin diameter diminishes, and we expect plasma properties to change accordingly. Based only on pin diameter considerations, radial foil explosions at 1 MA could produce magnetic pressures ranging from 160 kbar (for 2-mm pins) to 2.5 Mbar (for 0.5-mm pins). However, magnetohydrodynamic instabilities limit plasma performances. For large-diameter pins (2 mm), the force density is low, but the plasma is stable until the discharge current reaches 1.1 MA. For a smaller diameter (0.5 mm), instabilities appear when the discharge is 600 kA before the current peaks. While an increase in the local plasma electron density and temperature is noticeable as the cathode size diminishes, instabilities do limit overall plasma properties and require stabilization to obtain higher pressures.