Numerical study on high power microwave flashover and breakdown on output-window by EM-fluid simulation

Summary form only given. An electromagnetic-field FDTD method coupled with plasma fluid model is put forward to study the phenomena of High Power Microwave flashover and breakdown on output-window. 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/m³) 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 decrease the initial density or depth of plasmas; the other way is to shorten incident microwave pulse or decrease 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 varying with time; the plasma region move to the direction of microwave source; with strong-outgassing, output microwave pulse is shortened without cut-off, there are a “thread-like” ultra-high-density (~10²¹/m³) and ultra-thin (~mm) plasma regions with slow diffusion, the distance between two “thread-like” region 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 are lengthened but cut-off finally, there are a “belt-like” high-density (~10¹⁸/m³) 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, a “block-like” diffuse ultra-high-density (~10²¹/m³) and deep (~cm) plasma regions are formed with very fast diffusion, the shortening of output microwave is caused by plasma reflection mostly.