Fig. 1. Schematic of parallel shadow optical system

Fig. 2. Device for observing discharge shock wave by shadow method

Fig. 3. Structural diagram of discharge area

Fig. 4. Sequence diagram of image acquisition

Fig. 5. Generation and evolution of discharge shock wave. (a) Before discharge;(b) 6.5 μs; (c) 19 μs; (d) 28.5 μs; (e) 40 μs; (f) 63 μs; (g) 199 μs; (h) 285 μs

Fig. 6. Shock wave images from 20 μs to 31 μs. (a) 20 μs; (b) 21 μs; (c) 22 μs; (d) 23 μs;(e) 24 μs; (f) 25 μs; (g) 26 μs; (h) 27 μs; (i) 28 μs; (j) 29 μs; (k) 30 μs; (l) 31 μs

Fig. 7. Propagation path of transverse shock wave

Fig. 8. Locations of transverse shock wave from 20μs to 31 μs. (a) 20 μs; (b) 21 μs; (c) 22 μs; (d) 23 μs; (e) 24 μs; (f) 25 μs; (g) 26 μs; (h) 27 μs; (i) 28 μs; (j) 29 μs; (k) 30 μs; (l) 31 μs

Fig. 9. Propagation of shock wave of main electrode. (a) Generation stage of shock wave of main electrode; (b) encounter of shock waves of main electrode; (c) crossover of shock waves of main electrode; (d)(e) shock waves of main electrode continues to propagate; (f) shock waves of main electrode arrive at the opposite electrode

Fig. 10. Propagation of preionization shock wave. (a) Preionization shock wave location at 11 μs; (b) preionization shock wave location at 12 μs; (c) preionization shock wave location at 16 μs; (d) preionization shock wave location at 17 μs; (e) preionization shock wave location at 18 μs; (f) preionization shock wave location at 19 μs