Insulator surface breakdown in a simulated low Earth orbit environment

Surface flashover on insulators are investigated under UV irradiation or with a plasma background. A DC voltage up to 50 kV or a voltage pulse (up to 70 kV with 200 ns duration) is applied to the test gap, and the breakdown current, breakdown voltage, and soft X-ray emission are recorded by highly sensitive sensors with risetimes in the order of one nanosecond. Preliminary results with a plasma background have shown a more rapid development in the breakdown initiation compared to measurements in vacuum with no plasma. With a magnetic shielding technique using permanent magnets, the duration of an applied voltage pulse can be increased by a factor of 2 to 3 without causing flashover. UV illumination on the electrodes decreased the flashover voltage (for the DC case) or the voltage pulse duration without breakdown (for the pulsed case), whereas UV illumination on the dielectric surface enhanced the flashover potential.