A solid state pulse generator (DHVG1) as a grid bias supply for the MITTON

The MITTON is a high voltage closing and opening switch. The switch is triggered into conduction by the application of a microwave pulse (1 /spl mu/s, /spl ap/13 kW peak power) to a helical slow wave structure (helix) that surrounds the switch. The microwave fields ionise the low pressure gas inside the switch. Anode fall times of 10 ns have been measured for voltages up to 16 kV. The switch is opened by a negative bias pulse (1250 ns (FWHM), /spl ap/1 kV) applied to a large area metal grid. The applied negative potential results in the formation of a positive ion sheath, at the grid, leading to a reduction in the conduction area and hence an increase in the impedance of the switch. The DHVG1 solid state pulse generator has been designed as a grid bias supply for the MITTON. The generator uses a power MOSFET as the switching element. The new solid state generator, designed and built in-house, is based on a pulse generator used as a thyratron driver for a metal hybrid laser. The two main reasons for designing the new pulse generator were to try and prevent re-closure at the end of the bias pulse by the application of a suitable DC bias, and to apply higher bias voltages to the grid in order to open the switch at higher discharge currents. Preliminary results show that by applying a DC bias of the order of -100 volts the switch will remain open for up to 30 /spl mu/s, a factor of thirty greater than had been obtained with the previous pulse generator.