Structure of plasma sheath in a plasma focus device

Summary form only given. Experiments were conducted on a device consisting of a condenser bank with 81 μF at 20-30 kV. The propagation of the plasma sheath in the rundown phase and pinch phase was studied by laser interferometry. The di/dt signal and X-ray yield were measured at the same time. The velocity of the plasma sheath in the rundown phase reached 1.0×10⁷ cm/s at p=0.5 torr gas pressure. It decreased to 5.5×10⁶ cm/s at p=1.5 torr and then remained nearly unchanged up to 5 torr. The di/dt signal can be used to estimate the pinch compression. A better compression condition of the plasma gives a high di/dt value and high X-ray yield. The structure of the plasma sheath depend strongly on the gas pressure. The pinch pattern changes with the structure of the plasma sheath in the rundown phase. The structure of the plasma sheath in the rundown and pinch phases, the di/dt signal, and the X-ray yield are correlated