A Very Small Plasma Focus Operating at Tens of Joules

Abstract

A very small plasma focus device has been designed and set-up. The plasma focus operates in the limit of low energy (160nF capacitor bank, 65nH, 25–40kV, ∼ 32–100J). The design of the electrode was assisted by a simple model of a Mather plasma focus. A neutron yield of 104 – 105 is expected from discharges in deuterium. Experiments in H 2 have been performed at pressures from 0.1 to 2 mbar. The diagnostics used in the experiments include current derivative, voltage monitor, and plasma image using a ICCD camera gated at 5 ns. The umbrella-like current sheath running over the end of the coaxial electrodes and the pinch after the radial collapse can be clearly observed in the photographs. The velocity of the radial collapse is of the order of 105 m/s. The observations are similar to the results obtained with devices of much higher energies.