Displacement current and surface flashover

Abstract

High-voltage vacuum insulator failure is generally due to surface flashover rather than insulator bulk breakdown. Vacuum surface flashover is widely believed to be initiated by a secondary electron emission avalanche along the vacuum-insulator interface. This process requires a physical mechanism to cause secondary electrons emitted from the insulator surface to return to that surface. Here, it is shown that when an insulator is subjected to a fast high-voltage pulse, the magnetic field due to displacement current through the insulator can provide this mechanism. This indicates the importance of the voltage pulse shape, especially the rise time, in the flashover initiation process.

Measurements of an expanding surface flashover plasma

“…Because vacuum surface flashover presents one of the primary limits on the achievable electric field in vacuum devices, an improved understanding of this process and the methods to control it is critical for the development of advanced, compact devices. [2][3][4] However, the ability of these discharges to produce copious quantities of light and plasma has also been put to good use in systems as diverse as closing 5 and opening 6 switches, as well as electron, 7-9 ion, 10,11 x-ray, 12 UV, 13 and microwave 14 sources. In many of these applications, the velocity at which the plasma expands away from the discharge site is of great importance.…”

Plasma Cathode for a Short-Pulse Dielectric Wall Accelerator

“…DWAs use stacked pulse-forming lines (PFLs) to generate an accelerating field which is directly applied to the beam through a nonconducting vacuum boundary or "dielectric wall." The Program's early work on DWAs focused on developing components and system architectures for radiography and other applications [3]- [11]. This led to the recent demonstration of a 600-keV radiography-type DWA, which was successfully operated as a booster cell for the ETA-II induction linac [10].…”

Vacuum insulator development for the dielectric wall accelerator

“…Under such conditions, the magnetic field generated by the displacement current in the structure is sufficient to alter the trajectories of low energy electrons emitted from the insulator surface by field emission or secondary emission 24 . This may affect the strength of the vacuum insulators by influencing the secondary electron avalanche process.…”