Transient Behavior of Current Modulated 2-T Inductively Coupled Plasma

Abstract

Time-dependent thermal plasmas are not in an equilibrium condition even if they are operated at a very high pressure. Therefore, nonequilibrium modeling is required in order to understand the underlying physics. Unfortunately, substantial modeling complexities have prevented significant advancements in the state-of-the-art. This paper presents new information for the nonequilibrium situation where the electron temperature is generally assumed to be higher than the heavy particle or gas temperature. Calculations are done for a radio-frequency inductively coupled thermal plasma where the coil current is pulse modulated. The discharge medium is argon at one atmosphere of pressure. The high-level current (representing the on-time state) is 170 A and is reduced to 80% of the high-level current or 136 A during the off-time state. The on-time and off-time durations are 10 and 5 ms, respectively. The electron temperature is observed to be higher by a factor of two or three compared to the gas temperature in the cooler region of the discharge. The difference between electron and heavy-particle temperature is negligible in the plasma core. The temporal behavior of the electron and heavy-particle temperatures are similar during the off-time, whereas the electron temperature's response is much faster than that of the heavy particle during the on-time. The response of the electron temperature to a step change in input power is almost instantaneous and enhances the energy exchange mechanism through elastic collisions between electron and heavy particles.