EXPERIMENTAL STUDY OF A TIME VARYING GAS DISCHARGE

Abstract

A spatial and temporal fall characterization of plasma parameters, produced using time varying voltage, in parallel plate configurations is desirable as it has many important applications. One of the major important problem in treatment of radio frequency R.F. discharges is the evaluation of the electron energy distribution function (E.E.D.F.), the plasma density n., and electron temperature Te. Well understanding of plasma characteristics will lead to more plasma industrial applications. In order to understand the processes occurring in plasma, it is necessary to be able to make accurate spatial and temporal measurements of plasma parameters.

The goal of this study is to evaluate the E.E.D.F. in a medium pressure (0.1-5 Torr) non-Maxwellian collision dominated R.F. Argon and Helium discharges plasma using experimental methods.

To investigate the RF. plasma, experimental work is carried out. Three techniques are used for plasma investigation with Langmuir probe. The first technique is a D.C. power supply connected to the probe through chock filters to obtain varying plasma parameters over one hundred cycles. The second is a fast scanning method where a ramp generator is used to supply the probe voltage to estimate the plasma parameters averaged over few cycles.

A time-resolved Langmuir probe technique is used to measure the dependence of the plasma density, electron temperature, plasma potential, floating potential and electron energy distribution (EEDF) on the phase of the driving voltage in the discharge. The maximum electron temperature obtained during the positive part of the cycle and less value measured at negative part. The same pattern is reported for electron temperature and plasma density.