Electric current in dc surface flashover in vacuum

Abstract

Dielectric surface flashover in vacuum is characterized by a three-phase development, as shown by current measurements covering the range from 10−4 to 100 A, assisted by x-ray emission measurements, high speed photography, and time-resolved spectroscopy. Further information is gained from a comparison of the flashover dynamics at 77 and 300 K. Phase one comprises a fast (several nanoseconds) buildup of a saturated secondary electron avalanche reaching current levels of 10 to 100 mA. Phase two is associated with a slow current amplification, with a duration on the order of 100 ns, reaching currents in the ampere level. The final phase three is characterized again by a fast (nanoseconds) current rise up to the impedance-limited current on the order of 100 A in this specific apparatus. The development during phase two and three is described by a zero-dimensional model, where electron-induced outgassing leads to a Townsend-like gas discharge above the surface. The feedback mechanism towards a self-sustained discharge is due to space charges leading to an enhanced field emission from the cathode. A priori unknown model parameters, such as field enhancement factors, outgassing rate, and the buildup of the gas density above the surface, are determined by fitting calculated results to experimental data.

Increased surface flashover voltage in microfabricated devices

“…Electrons hop across the dielectric surface, which desorbs gas molecules from the surface leading to a Townsend-like breakdown through this gas layer. [26][27][28] This is a function of the number of desorbed gas molecules per unit area at the point of flashover, M cr , the electron emission and impact energies, A 0 and A 1 , respectively, the efficiency of electron stimulated gas desorption, c, molecule ejection velocity, v 0 , electron velocity, v e , which is given by v e ¼ 5:94 Â 10 5 ffiffiffiffiffi A 1 p m=s, 27 and h which is the angle that electrons are emitted from the triple point. The point at which the dielectric, cathode, and vacuum meet, given by tanh…”

“…Unfortunately, there is only a limited amount of information regarding M cr , c, and v 0 , with measurements ranging over several orders of magnitude for different experimental setups, [26][27][28][29] and A 1 is only known for a handful of common dielectrics. 30 Therefore, we will treat u as a fitting parameter to compare between static and rf measurements and between different fabrication processes.…”

“…The result of introducing a ground plane is that the electric field deviates significantly from the uniform electric field typically assumed in SEEA models. [26][27][28] This modification of the electric field increases the electric field magnitude near the metal, dielectric, and vacuum interface, and introduces an electric field perpendicular to the dielectric surface. To investigate how a conducting substrate or ground plane effects flashover, measurements were performed on PECVD aSiO deposited on a silicon wafer.…”

Theoretical and simulation research on self-stabilizing secondary electron emission process across solid dielectrics in vacuum

“…17 Neuber et al proposed three stages of flashover in vacuum and calculated the current across insulator surface at these stages. 18 In order to confirm the process of SSEE, a onedimension steady Mont Carlo simulation is applied to reveal the surface charge accumulation process on insulators with planar electrode system under DC voltage excitation, as shown in Fig. 4.…”

Surface Electric Field Analysis of Insulating Material with Transitional Permittivity in Vacuum

“…For the insulating material with a low conductivity and a high permittivity like fused quartz, it takes a long time of 105 s to establish a steady electric field under a constant voltage excitation [2] during the time of 0 to 105 s, the field distribution mainly depend on the permittivity of the material, especially at the beginning. As we know, a flashover event generally occurs with a duration at the magnitude of 100 ns [3]. So when investigating the flashover characteristic of insulators under an alternating voltage excitation or an impulse voltage or even a constant voltage excitation in a short time, the permittivity of the insulator should be paid great attention.…”