Magnetic insulation of dielectric surfaces in vacuum using DC magnetic fields

Abstract

The influence of dc magnetic fields on dielectric surface breakdown in vacuum using pulsed test voltages is investigated. Predictions from the "saturated surface avalanche" breakdown model and the experimental results show-magnetic insulation effects, i.e., an increase in flashover voltage, at magnetic field amplitudes as low as 0.1 T. The magnetic field is oriented parallel to the insulator surface and perpendicular to the electric field. An increase in flashover voltage is seen for the magnetic field direction where the ExB drift is away from the surface, while a decrease followed by an increase in flashover voltage is seen for ExB drift into surface. The magnitude of the insulation effect depends on the dielectric material, ambient pressure, surface roughness, and presence of background plasma. In order to achieve magnetic insulation with and without a background plasma, it is sufficient to apply the magnetic field in the cathode region only. Magnetic insulation has also been observed using small low weight permanent magnets which can be used to increase the flashover voltage in a low density plasma environment where the electron density is on the order of W cm-3. The dependence of the flashover voltage on the square root of the gap distance is retained with the application of an insulating magnetic field. Also, prebreakdown luminance measurements support the "saturated surface avalanche" model.