Gas discharge theory for the POLOTRON

The POLOTRON is a microwave-triggered thyratron type high voltage closing switch, with an annular geometry. Two high voltage gaps are separated by a grid region and are triggered into conduction by the plasma formed in the grid region when a high power microwave pulse (≈13 kW, 1 μs) is applied to a helix surrounding the switch. We use (insulating) wall-stabilised gas discharge theory to estimate plasma parameters (number density distribution, axial electric field and electron temperature) in the grid region of the POLOTRON, when a current flows through the switch and the charging network discharges through the load. The results are used to ascertain the effects of varying the switch geometry on plasma parameters. The results may also be used as a first order approximation of the discharge parameters for a microwave-triggered opening and closing switch (the MITTON); in the MITTON, the presence of a conducting wall increases the charged particle losses and hence the electron temperature and field