Methods of increasing the surface flashover potential in vacuum

The effects of surface coating and magnetic fields on dielectric surface breakdown in vacuum are described. Coatings of metals and meta oxides increase the pulsed surface hold-off voltage by factors of up to three, depending on the material. Measurements of the secondary emission coefficient show substantial differences between coated and uncoated samples at high energies. The influence of magnetic fields on dielectric surface breakdown for uncoated samples is investigated in the pressure range of 10^-5 to 1 Pa, for both DC and pulsed electric and magnetic fields. Insulation effects (increase in breakdown voltage of up to 2× at magnetic field amplitudes of 0.5 T) are observed when the magnetic field is parallel to the surface of the dielectric and perpendicular to the applied electric field. Magnetic insulation shows a strong material dependence and decreases with increasing pressure and surface roughness