Transition from unstable electrostatic confinement to stable magnetic confinement in a helicon reactor operating with Ar/ SF 6 gas mixtures

C.S. Corr (1) , Nicolas Plihon (1) , Pascal Chabert (1)

1 LPTP - Laboratoire de Physique et Technologies des Plasmas

Two types of instabilities were previously identified in inductive discharges having an expanding chamber when negative ions are present: ͑i͒ the source instability, occurring in the neighborhood of the capacitive-to-inductive ͑E to H͒ transition, and ͑ii͒ the downstream instability, which was shown to be the periodic formation and propagation of double layers. These unstable double layers were found over the entire parameter space ͑pressure/power͒ of interest, and they were born at the interface of the source and diffusion chambers. They acted as an internal electrostatic barrier separating a low-electronegativity, high-electron-density plasma upstream ͑in the source͒ and a high-electronegativity, low-electron-density plasma downstream. In this paper we have investigated the effect of adding a static axial magnetic field, classically used to increase the confinement and the plasma heating via helicon wave propagation. This had the following consequences: ͑i͒ the unstable double layers, and therefore the axial electrostatic confinement, were suppressed in a large part of the parameter space, and ͑ii͒ the magnetic confinement leads to a radially stratified plasma, the center being a low-electronegativity, high-density plasma and the edges being essentially an ion-ion plasma.

Domaines: Physique des plasmas [physics.plasm-ph]

C.S. Corr, Nicolas Plihon, Pascal Chabert. Transition from unstable electrostatic confinement to stable magnetic confinement in a helicon reactor operating with Ar/ SF 6 gas mixtures. Journal of Applied Physics, 2006, 99, pp.103302. ⟨10.1063/1.2191431⟩. ⟨hal-01140494⟩