Numerical investigation on high power microwave flashover and breakdown on inner and outer surface of output-window by EM-fluid simulation

Abstract

In this paper, an electromagnetic-field FDTD method coupled with plasma fluid model is put forward to investigate the different physical phenomena of high power microwave (HPM) flashover and breakdown on inner and outer surface of output-window. Based on the above theoretical models, a one-dimensional (1D) electromagnetic field and plasma interaction code is programmed by authors. By using the code, the HPM flashover and breakdown on inner and outer surface of output-window are simulated. The numerical results could be concluded as follows. For flashover and breakdown on outer surface, output microwave pulse is shortened without cut-off; there is a standing-wave distribution of electric field RMS (Root-Mean-Square) value before the window with fixed-positions of wave nodes and antinodes; there is a ultra-high-density (～1021 m-3) and ultra-thin (～mm) plasma shell with slow diffusion, microwave could penetrate the plasma-shell partly; the shortening of output microwave is caused by plasma absorption mostly. The output pulse of microwave could be lengthened by reducing the initial density or depth of plasmas; the other way is to shorten incident microwave pulse or reduce the value of incident microwave power. For flashover and breakdown on inner surface, there is also a standing-wave distribution of electric field RMS value before the window but the positions of wave nodes and antinodes vary with time; the plasma region moves toward the microwave source; with strong-outgassing, output microwave pulse is shortened without cut-off, there are “thread-like” ultra-high-density (～ 1021 m-3) and ultra-thin (～mm) plasma regions with slow diffusion, the distance between two “thread-like” regions is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and low electric field value, the output pulse of microwave is lengthened but cut-off finally, there are “belt-like” high-density (～ 1018 m-3) and thin (mm-cm) plasma regions with fast diffusion, the distance between two “belt-like” region is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and high electric field value, output pulse of microwave is cut-off quickly, “block-like” diffuse ultra-high-density (～1021 m-3) and deep (～ cm) plasma regions are formed with very fast diffusion, and the shortening of output microwave is caused by plasma reflection mostly.

Effect of desorbed gas on microwave breakdown on vacuum side of dielectric window

“…Compared to experimental research, more theoretical studies were devoted to exploring the effect of desorbed gas on microwave window breakdown in vacuum [12,[15][16][17][18][19]. Wang used the electrostatic particle-in-cell-Monte Carlo collision (PIC-MCC) model to numerically simulate the window breakdown involving desorbed gas [15].…”

“…Cheng investigated numerically the suppression of window breakdown by an external magnetic field when considering the influence of desorbed gas [16]. Under different yields and speeds of desorbed gas molecular, the electrostatic PIC-MCC model was employed by Dong to simulate the changes in the number and mean energy of electrons over time [17][18][19]. This study also discussed the influence of desorbed gas on the spatial distribution of charged particle density and normal electric field.…”

“…The breakdown plasma absorbs and reflects the microwave, and leads to changes in the microwave fields. Nevertheless, we still do not have a sufficient understanding of this phenomenon because the electrostatic PIC-MCC model was usually used in previous studies [12,15,[17][18][19]. In this paper, the electromagnetic PIC-MCC model is used to investigate the evolution of dielectric surface breakdown involving desorbed gas.…”

A hybrid mode of one- and two-surface multipactor on grooved dielectric surface

“…The former often occurs on the RF window surface or insulator surface, requires an applied electric field parallel to the dielectric surface and a direct current (DC) electric field from the charging of the dielectric surface, and has been profoundly investigated experimentally, theoretically, and numerically. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] The latter requires a resonant RF electric field perpendicular to the plate surface, and often occurs on the waveguide or metal gap. [1,22] Despite the extremely similar physical process, they are always thought to occur on different devices solely and are studied by researchers from different fields separately.…”