High and low frequency relaxation oscillations in a capacitive discharge plasma

Both high and low frequency relaxation oscillations have beenobserved in an argon capacitive discharge connected to a peripheralgrounded chamber through a slot with dielectric spacers. Theoscillations, observed from time-varying optical emission of themain discharge chamber, show, for example, a high frequency(46,kHz) relaxation oscillation at 100,mTorr, with an absorbedpower near the peripheral breakdown, and a low frequency(2.7--3.7,Hz) oscillation, at a higher absorbed power. The highfrequency oscillation is found to ignite a plasma in the slot, butusually not in the periphery. The high frequency oscillation isinterpreted by using an electromagnetic model of the slot impedance,combined with the circuit analysis of the system including amatching network. The model is further developed by using a parallelconnection of variable peripheral capacitance to analyse the lowfrequency oscillation. The results obtained from the model are inagreement with the experimental observations and indicate that avariety of behaviours are dependent on the matching conditions.