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.Index Terms-Chemical nonequilibrium, duty factor, kinetic nonequilibrium, local thermodynamic equilibrium (LTE), response time, simmer current level (SCL). Khokan C. Paul (M'99) received the B.Sc. degree in electrical and electronic engineering from Bangladesh Institute of Technology, Chittagong, Bangladesh, in 1990, and the M. Eng. and Ph.D. degrees from the