Bubble to jetting mode transition mechanism of plasmas in salt solutions sustained by pulsed DC power

Summary form only given. Diagnostic studies of plasmas in NaNO₃ solutions are presented. The plasma is driven by a pulsed DC power with a 100 Hz repetitive pulse frequency, an applied voltage up to 600 V, and T_on from 10 to 500 μs. A Pt wire 0.5 mm in diameter covered with a glass tube is used as the plasma generating electrode. This electrode is facing upward. A bare Pt wire is used as the grounding electrode. Solution concentrations of 0.02 to 1 M are used. The bubble behavior and the plasma characteristics are strongly influenced by the applied voltage and T_on. With T_on=25 μs at 200 V, the bubble mode is observed. In this mode, bubbles with hundreds μm in diameter are formed and continuously detached from the electrode surface. With an increase in T_on or the applied voltage, a transition to the jetting mode is seen. In this mode, a large number of much smaller bubbles are jetted away from the surface. Calculation of the power and energy input within each power cycle for various applied voltage, T_on, and solution concentrations shows that the bubble to jetting mode transition occurs when the power and energy input exceed 45 W and 4*10^-3 J, respectively. Such an observation strongly suggests that the bubble to jetting transition is induced by electrothermal effect.