Current sheath studies in a small plasma focus operating in hydrogen-argonmixtures

We present preliminary time and space resolved studies of current sheath fo rmation in Plasma Focus discharges, using a novel array of non-invasive mag netic field probes. The experiments are performed in a Mather type plasma f ocus, operating at 2 kV. The discharge is formed between a hollowed anode a nd six symmetrically arranged cathode rods. The array of small magnetic pro bes is located along the cathode rods. The probes are of millimeter size. T hey are shielded behind the rods, as to minimize capacitive coupling to the anode electrode, and allow nan-perturbing measurements to be made. A simpl e analytical model of current sheath evolution is used to analyze the probe signals. The experiments have been performed in pure Hydrogen and Hydrogen with Argon mixture, at pressures from below 0.2 Torr upwards. The effect o f the Argon mixture on the current sheath structure is investigated with th e probe array. It is found that at constant mass density operation, the inc rease in the percentage of Argon results in a thinner sheath, with steeper current profile.