Comparison between Theoretical and Experimental Radial Electron Temperature Profiles in a Low Density Weakly Ionized Plasma

Ahmed Rida Galaly,Guido Van Oost

doi:10.4236/jmp.2019.107050

Abstract

Experimental and theoretical studies of the radial distribution function of the electron temperature (RDFT) in a low-density plasma and weakly ionized gas for the abnormal glow region are presented. Experimentally, the electron temperatures and densities are measured by a Langmuir probe moved radially from the center to the edge of the cathode electrode for helium gas at different pressures in the low-pressure glow discharge. The comparison of the final experimental data for the radial distribution of electron temperatures and densities for different low pressures ranging from 0.2 to 1.2 torr, with the final proved equation of RDFT confirms that the electron temperatures decrease with increasing product of radial distance and gas pressures, showing a radial decrement dependence of the electron temperature from the center to the edge of the electrode. This is attributed to the increase of the number of electron-atom collisions at higher gas pressures and consequently of the rate of ionization. For the axial distance (L) from the tip of the probe to cathode electrode and the cathode electrode radius (R), a theoretical and experimental comparison for the two conditions L R, for both cases the produced plasma temperatures decrease and densities increase. It is concluded that the RDFT accurately shows a dramatic decrease for L R similar as for conditions of magnetized and unmagnetized effect for DC plasma. This means that the rate of plasma loss by diffusion decreased for L < R, agrees well with the applied of magnetic field behavior

Highlights

Plasma is the fourth state of matter, considered to be a quasi-neutral medium
The electron temperatures and densities are measured by a Langmuir probe moved radially from the center to the edge of the cathode electrode for helium gas at different pressures in the low-pressure glow discharge
The comparison of the final experimental data for the radial distribution of electron temperatures and densities for different low pressures ranging from 0.2 to 1.2 torr, with the final proved equation of radial distribution function of the electron temperature (RDFT) confirms that the electron temperatures decrease with increasing product of radial distance and gas pressures, showing a radial decrement dependence of the electron temperature from the center to the edge of the electrode

Summary

Introduction

Plasma is the fourth state of matter, considered to be a quasi-neutral medium. when a diagnostic such as probe (a small metallic electrode) is inserted into a weakly ionized plasma, a very thin sheath is formed around the conducting surface of the probe due to the redistribution of charges. Ambipolar diffusion is the most important process taking place within a weakly ionized plasma and considered as a vital process for the distribution of the plasma parameters. The experimental and numerical radial distribution of electron temperature and density from the axis of the tube up to the tube wall have been amply investigated [9] [10], but not the theoretical derivation in terms of the effect of Schottky condition and ambipolar diffusion due to the recurrence relation of the Bessel condition. An experimental study of the radial dependence of the electron temperature in a low-density plasma using a single probe as diagnostic technique was performed. The theoretical considerations are compatible with the experimental data of the temperatures at different pressures in a low-pressure glow discharge of a DC (cold cathode) magnetron sputtering unit

Experimental Set-Up

Experimental Study of Radial Dependence of the Electron Temperature

Nex109 cm-3 4

Findings

Conclusion