The bubble to jetting transition mechanism of plasmas in NaNO3 solutions sustained by pulsed power

Plasmas in NaNO3 solutions sustained by pulsed power with Ton = 10-500 µs are studied. With an applied voltage equal to or lower than 100 V, the bubble mode is observed. In this mode, bubbles, a few hundred μm in diameter, are formed and detached continuously at the electrode surface because of the buoyant force. An increase in the applied voltage to 125 V results in a bubble to jetting transition. When this transition occurs, bubbles with diameters smaller than 100 µm are formed and are rapidly jetted away continuously. The examination of various conditions shows that the transition occurs when the power and energy input simultaneously exceed critical values 4.4 × 10-3 ± 6 × 10-4 J and 45 ± 5 W, respectively, within Ton. Given the electrode surface area, this critical power is equivalent to a heat flux of 229 ± 25 MW m-2, which is close to the heat flux required, 223 MW m-2, for the occurrence of explosive vaporization reported in the literature. Such an observation strongly supports the hypothesis that the bubble to jetting transition is induced by the electrothermal effect.