Preliminary studies on a plasma focus opening switch

The small plasma focus device UNUIICTP PFF has been modified to assess the operation of a plasma focus based long conduction (> 2 µs) opening switch, with a plasma filled diode as the load. The UNUIICTP PFF is a Mather type plasma focus device powered by a single 15 kV, 30 µF capacitor delivering a peak current of 150 kA when discharged at 15 kV. The device has been optimised for reproducible focusing in various gases including deuterium, argon, carbon dioxide, helium as well as in air. In particular, the optimum operating pressure for air is between 0.5 to 1.1 mbar, whereas for argon it is between 0.3 to 3 mbar. For the operation of the UNUIICTP PFF as an opening switch, the electrodes geometry is modified to redirect the plasma motion at the end of the axial rundown phase to avoid the normal plasma focus action, and the operating regime is shifted to low pressure to favour plasma opening switch action. With air as the working gas, pressure as low as 10⁻³ mbar has been tested. At such a low pressure, a set of twelve plasma injection cable guns is used to initiate breakdown of the discharge. The design and operating principle is presented and some preliminary results obtained on the operational characteristics of this device are discussed