AN EMISSION-BASED FEEDBACK-SYSTEM FOR STABILIZING AN INDUCTIVELY COUPLED PLASMA

An emission-controlled feedback system for stabilizing an ICP (Inductively Coupled Plasma) has been investigated. Unlike previous stabilization methods which monitor only the power being sent to the plasma, the present one uses an emission signal from either argon or an internal reference element as a stability indicator. Using a previously constructed power-modulation circuit for rf power control, the feedback network adjusts the plasma power to compensate for changes in the emission level of the reference element. It is shown to be particularly useful for reducing or eliminating the drift that occurs when the plasma is warming up. Results with several combinations of argon, barium, calcium, iron, manganese, sodium, and strontium lines are presented.