Observation of low-frequency oscillation in argon helicon discharge

Abstract

We present here a kind of low-frequency oscillation in argon helicon discharge with a half helical antenna. This time-dependent instability shows a global quasi-periodic oscillation of plasma density and electron temperature, with a typical frequency of few tens Hz which increases with external magnetic field as well as RF power. The relative oscillation amplitude decreases with magnetic field and RF power, but the rising time and pulse width do not change significantly under different discharge conditions. The oscillation can only be observed in some specific conditions of low magnetic fields and low RF power when the gas flows in from one end of the discharge area and out of from another end. This global instability is suggested to be attributed by the pressure instability of neutral depletion, which is the result of compound action of gas depletion by heating expansion and gas replenishment from upstream. There are two kinds of oscillations, the large and small amplitude oscillations occurring in different discharge modes. This study could be a good verification and complement of earlier experiments. This kind of spontaneous pulse phenomenon is also helpful to realize the pulsing plasma source without the pulsed power supply.