Striation characteristics of a DC driven water vapor plasma operating at moderate pressures

In this work striation characteristics in moderate pressure water vapor plasma driven by a dc power source are studied. The experiments are conducted over a range of pressure conditions (2 – 15 Torr) with an inter-electrode separation of 4 cm. Distinct striations were observed at 8 Torr, for a resulting ‘pd’ of 32 Torr-cm. Striations starts appearing at ~ 6 mA and exists till 15 mA (limit of power supply unit) which coincides with the normal glow regime of operation. The number of striations appears to decrease with increasing current – consistent to prior studies reported in the literature. Temporal current and voltage measurement show the discharge current and voltage to oscillate in the striation region, where the discharge current and voltage oscillated with a ~ 1 – 2 mA, and ~35 – 60 V amplitude respectively with a frequency of ~ 100 kHz. High speed image acquisition reveals the plasma discharge to oscillate at ~ 100 kHz with striations forming as the positive column of the discharge starts to form and extend towards the ground electrode. These results indicate the possibility of circuit driven instability playing a role in the observed oscillatory pattern. Additional numerical analysis is being conducted to reveal the details of the phenomena.

Keywords: Striation, Polyatomic Gas, Moderate Pressure, DC glow