Low-frequency breathing instabilities induced by intense plasma-gas heating.

Instabilities are a common occurrence in plasma discharges where they play an important role in system behavior and performance. While such instabilities are typically in the kHz and MHz range, this work reports a low frequency (∼100Hz) instability observed in supersonic inductively coupled plasmas. Using a novel swirl gas injection, two concentric, counter-propagating vortices are produced that segment the flow field. While discharge properties only vary moderately within the outer vortex, intense plasma-gas heating leads to pressure fluctuations that drive a large-amplitude instability within the inner vortex. By adjusting the injection conditions, the instability can be damped or amplified.