X-band microwave generation caused by plasma-sheath instability

TL;DR

This paper reports the first observation of prolonged, high-frequency (tens of GHz) plasma sheath oscillations caused by electron transit-time effects, with potential applications in plasma diagnostics.

Contribution

It demonstrates the elimination of ionization effects to sustain plasma sheath oscillations at much higher frequencies than previously achieved.

Findings

Oscillations sustained during entire positive bias application

Oscillation frequency increased to tens of GHz

Oscillation power reached tens of milliwatts

Abstract

It is well known that oscillations at the electron plasma frequency may appear due to instability of the plasma sheath near a positively biased electrode immersed in plasma. This instability is caused by transit-time effects when electrons, collected by this electrode, pass through the sheath. Such oscillations appear as low-power short spikes due to additional ionization of a neutral gas in the electrode vicinity. Herein we present first results obtained when the additional ionization was eliminated. We succeeded to prolong the oscillations during the whole time a positive bias was applied to the electrode. These oscillations could be obtained at much higher frequency than previously reported (tens of GHz compared to few hundreds of MHz) and power of tens of mW. These results in combination with presented theoretical estimations may be useful, e.g., for plasma diagnostics.