Characterisation of the opening switch action in a modified plasma focus

The small plasma focus device, UNU/ICTP PFF is modified to operate as a long conduction (>2 μs) opening switch. A plasma filled diode is used as the load. The UNU/ICTP PFF is a Mather type plasma focus device powered by a single 15 kV, 30 μF capacitor delivering a maximum current of 150 kA when discharged at 15 kV. In the experiments, the modified UNU/ICTP PFF is discharged at 14.5 kV at its optimum operating pressure range of 1.0×10^-2 mbar to 3.5×10^-2 mbar in air. The electrode geometry of the UNU/ICTP PFF is modified to redirect the plasma motion in order to avoid the normal plasma focus action. At such a low pressure, a set of twelve additional injection plasma guns is utilised to initiate breakdown of the discharge. These guns are mounted near the back-wall of the focus tube and provide the initial ionization path for discharge formation. These guns are initiated about 80 ns after the voltage is established across the focus electrodes. A plasma filled diode is arranged to sit directly 10 mm on top of the switch to act as the load. The role of the diode is to allow a small portion of the switch plasma to pass from the switch section into the diode section through a series of apertures