Pressure in underwater spark discharge initiated with the help of bubble injection and its evaluation based on H-alpha line broadening

Abstract The pressure in an underwater discharge channel is the main parameter that influences all its applications. In this study, we investigate a relatively large gap with plane-to-plane electrode geometry uses assistance of injected gas bubble for breakdown. delay application high voltage following injection from grounded determines initial dimensions bubble. We examined three types discharge: (a) easy triggering, (b) medium bubble, and (c) small difficult triggering. diagnostic tool H α line broadening. It shown (i) Doppler broadening plays no role; (ii) at broadening, resonance van der Waals broadenings must be considered; (iii) impact approximation not applicable, hence quasi-static high-pressure (namely ‘nearest neighbour’) used; (iv) Stark dominant role. Because mixture two gases (evaporated water vapour nitrogen injection) present channel, simple thermodynamic considerations were applied to estimate ratio contributions larger smaller detected channel. This agreement measurements wave amplitude certain distance using piezoelectric probe.