The instability occurs at the sheath-plasma resonance and is driven by the negative differential resistance of the rf sheath associated with electron inertia. It resembles the monotron oscillations in diodes analyzed by Llewellyn. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening, and copious harmonics. Emission lines vs afterglow time at fixed receiver frequency, where harmonics of the sheath-plasma instability are identified. The fundamental instability is a bounded oscillation in an evanescent plasma, but the harmonics are radiated as electromagnetic waves from the electrodes acting as antennas.
Emission frequencies vs afterglow time produced by a spherical rf electrode.
The line broadening mechanism has been identified as a frequency modulation caused by the ion dynamics which effects the electron transit time. Ion oscillations create repetitive bursts of electromagnetic radiation. Fundamental emission line vs afterglow time. Return to Research Topics list. Return to Home page.