The early phase of dielectric surface flashover in a simulated Low Earth Orbit environment

In Low Earth Orbit (LEO) the environment space plasma and UV radiation influences the surface charging and the surface flashover voltage of insulators, and thus the performance of high voltage systems. Understanding the mechanisms leading to surface flashover will make it possible to apply certain shielding techniques (e.g. electric and magnetic shielding) which can increase the dielectric flashover voltage drastically. In our experimental apparatus, a dc voltage up to 50 kV or a voltage pulse (up to 100 kV with 200 ns duration) is applied to the test gap. The geometry of all interconnecting lines and of the discharge chamber is coaxial and the impedances are closely matched. Breakdown current and voltage are recorded by highly sensitive sensors with risetimes of less than 0.8 ns. Preliminary results with a plasma background have shown a change from a surface dominated flashover to a plasma dominated breakdown compared to measurements in vacuum with zero plasma density. With applied UV radiation the dielectric flashover voltage amplitude decreases and the voltage and current waveform is altered, compared to results without UV, indicating a different current amplification mechanism in the early phase of dielectric surface breakdown.