The Influence of an External Permanent Magnetic Field on the Dynamics of Plasma Channels in a Radial Pseudospark Switch

Abstract

High-current gas discharges can reach current densities of 10 8 A/cm 2 in order of magnitude and, therefore, damage the electrodes of nearly all types of low-pressure gas discharge switches. In pseudospark switches with radial geometry, the total current is divided by the number of radial channels and so the current per channel is strongly reduced. However, because of electromagnetic forces the plasma channels attract themselves and pinch together already in the first maximum of the switching current. Therefore, the main advantage of the radial pseudospark switch, the division of the total current, is lost. In this paper, a basic idea of how this movement of the plasma channels can be suppressed, will be introduced. Strong permanent magnets of different types (polarization of type A: 0.48 T; type B: 1.31 T; and type C: 1.88 T) are attached to the pseudospark switch near the bores of the hollow cathode. The most effective way to apply the magnets was to put them face to face with the bores of the hollow cathode with the center line of the bores and the cylindric magnets coinciding. In this case, the magnetic field looks like a magnetic bottle viewed along the charge carriers path. The magnetic fields capture the plasma channels for a short time and so the pinch effect is delayed until the first maximum of current is over. The investigated pseudospark switch was a radial switch with three channels. The charging voltage was 10 kV and the discharge capacity was 2.2 F, resulting in a total discharge current of 40 kA, respectively, 13.3 kA per channel. In the switch under consideration, the pinching is fulfilled after 800 ns when no magnets are applied. The smallest possible distance between the front of the magnet and the end of the discharge channel was 2 mm. The strength of the magnetic field in this distance with magnets of type A, B, and C was 390, 1065, and 1525 mT, respectively, and the pinching was delayed for 400, 2000, and 1600 ns, accordingly.Index Terms-Electrode erosion, external magnetic field, pinch effect, pseudospark switch.