Instabilities in low-pressure inductive discharges with attaching gases

Plasma instabilities at frequencies 1 Hz-900 kHz have been observed in low-pressure inductive processing discharges with attaching gases. Instability windows in pressure and driving power are found. A volume-averaged (global) model of the instability is developed, considering idealized inductive and capacitive energy deposition. As pressure or power are varied to cross a threshold, the instability is born at a Hopf bifurcation, with relaxation oscillations between inductive and capacitive modes causing modulations of charged particle densities, electron temperature, and plasma potential. The oscillations can be so strong that the potential collapses and negative ions flow to the walls. (C) 1999 American Institute of Physics. [S0003-6951(99)03849-8].