Fig. 1. Schematic of gas discharge generating non-equilibrium plasma

Fig. 2. High-voltage large-volume discharge with limited current density. (a) Array needle cathode discharge with ballast resistance^[12];(b) dielectric barrier discharge plasma jet source structure and discharge image^[15];(c) capillary plasma pelectrode^[16];(d) laser microscopic image of DBD-based plasma display front substrate transformed into CPED structure and laser micrograph of the capillary on the surface of the medium^[17]

Fig. 3. Schematic diagram of the discharge device of the plasma cathode. (a) Schematic of the laser discharge device using a plasma electrode in which the relative timing of the volume discharge and the surface discharge can be controlled^[19];(b) schematic for the post-acceleration experiment of the plasma cathode discharge electron beam^[20];(c) self-breakdown-based single-gap plasma cathode electron gun^[21];(d) high current linear aperture radial multichannel pseudospark switch^[22];(e) a tapered multi-gap multi-aperture pseudospark-sourced electron gun based X-band slow wave oscillator^[23]

Fig. 4. Micro-hollow electrode structure and volt-ampere characteristic curve ^[7]

Fig. 5. Several representative micro hollow cathode discharge structures^[29-33].(a) Micro hollow discharge electrode structure and 2×2 array hollow cathode discharge photos；(b) micro hollow discharge etching silicon substrate device and etched silicon hole SEM photo；（c） micro hollow cathode structure of inverted pyramid and 10×10 array discharge photos；（d） linear array discharge device composed of micro hollow cathode discharge unit

Fig. 6. Capillary micro hollow cathode discharge ^[35]. (a) Schematic diagram of hollow cathode plasma mini-jet generator and optical test; (b) four-tube circuit with single power supply and ballast resistance;(c) photograph of argon plasma micro-jet discharge when the distance between electrodes is 2 mm

Fig. 7. Glow discharge maintained by micro hollow cathode discharge^[7]

Fig. 8. Micro hollow cathode excited dielectric barrier discharge electrode structure^[41-42].（a） Schematic diagram of CM-DBD experiments;（b） schematic drawing of the combined MHCD-DBD electrode system