Investigation of the delay time distribution of high power microwave surface flashover

Abstract

Characterizing and modeling the statistics associated with the initiation of gas breakdown has proven to be difficult due to a variety of rather unexplored phenomena involved. Experimental conditions for high power microwave window breakdown for pressures on the order of 100 to several 100 torr are complex: there are little to no naturally occurring free electrons in the breakdown region. The initial electron generation rate, from an external source, for example, is time dependent and so is the charge carrier amplification in the increasing radio frequency ͑RF͒ field amplitude with a rise time of 50 ns, which can be on the same order as the breakdown delay time. The probability of reaching a critical electron density within a given time period is composed of the statistical waiting time for the appearance of initiating electrons in the high-field region and the build-up of an avalanche with an inherent statistical distribution of the electron number. High power microwave breakdown and its delay time is of critical importance, since it limits the transmission through necessary windows, especially for high power, high altitude, low pressure applications. The delay time distribution of pulsed high power microwave surface flashover has been examined for nitrogen and argon as test gases for pressures ranging from 60 to 400 torr, with and without external UV illumination. A model has been developed for predicting the discharge delay time for these conditions. The results provide indications that field induced electron generation, other than standard field emission, plays a dominant role, which might be valid for other gas discharge types as well.

Multi-component non-stationary exponential distributions of the breakdown voltages and time delays in neon ramp breakdown experiments

“…6 The stochastic nature of breakdown time delay was experimentally proven by Zuber,7 while its exponential distribution was theoretically confirmed by von Laue. 8 Besides dc electrical breakdowns of gases, when voltage pulses applied to the discharge gap are constant, [9][10][11] the time varying voltage pulses are also applied, such as linearly rising ramps, 12,13 triangular, 14,15 ac with linearly rising amplitude, 16,17 microwave, 18,19 etc. Unstable physical conditions in the experiment (e.g., cathode conditioning, wearing or aging) also affect the breakdown processes.…”

Simultaneous measurement of nitrogen and hydrogen dissociation from vacuum ultraviolet self-absorption spectroscopy in a developing low temperature plasma at atmospheric pressure

“…3 Recent studies 4 of the effects of UV radiation on fast plasma formation have been focused on wavelengths longer than 200 nm, due to the complexity of measuring vacuum ultraviolet (VUV) radiation at atmospheric pressures. However, VUV radiation has been shown 5 to dramatically increase electron production rates from photo-ionization, and recent studies 6 have investigated the temporal relationship of VUV emission during the early stages of spark plasma formation.…”

Multipactor susceptibility on a dielectric with a bias dc electric field and a background gas

“…1 It may occur when a metallic gap or a dielectric surface is exposed to an ac electric field under some favorable conditions, and its avoidance has been a major concern among workers on high power microwave (HPM) sources, rf accelerators, and space-based communication systems. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] RF window breakdown or dielectric failure [2][3][4][5][6][7][8][9][10][11] has been a limiting factor in many high power microwave systems. In general, an avalanche of secondary electrons caused by multipactor discharge occurs in the prebreakdown phase.…”

“…Further ionization caused by these electrons provides a gaseous-like discharge (sometimes called flashover) within the desorbed gas layer, and it eventually turns into the breakdown phase of the dielectric. [7][8][9] Due to the high susceptibility of multipactor discharge on dielectric, 4-6 a small amount of seed electrons may grow to a high level that will initiate the breakdown of dielectric. To prevent the breakdown, it is necessary to suppress or eliminate the initial multipactor discharge.…”