Electromagnetic Wave Propagation In A Nonuniform Atmosphereic Pressure Plasma And An Experimental Study On A Low-pressure Capacitively Coupled Plasma

The thesis includes two parts.The first part focuses on the propagation of an Electromagnetic (EM) wave in Atmospheric Pressure Plasma (APP) slab. The wave propagation is described with an integral-differential wave equation, and solved numerically by the arithmetic of average conceal difference method combined Simpson integral method. The behaviors of the wave depended on the plasma parameter are discussed. The phase shift is increasing with the width and electrons density of the plasma slab, the attenuation of transmission wave become largest when the electron-neutral collision frequency equal to the EM wave angular frequency; the reflection is determined by the spatial gradient of the electrons density and average electron density. Besides collision absorption, there is evidence of resonant mode conversion of the incident EM wave into the electrostatic wave near the critical density region in the plasma slab,and the energy of the electrostatic wave transfer to the electrons through collisional damping or Landau damping. When the electrons-neutral collision frequency is less than the EM angular frequency, the collision absorption rates increase with the electron-neutral collision. When electrons-neutral collision frequency is larger than the EM angular frequency, the collision absorption rate will decrease with the electron-neutral collision frequency. In the last, our numerical results are compared with Appleton's Equation derived from WKB approximation. The two kinds of results match very well when the electrons density profiles are gentle in space. But, the departure of Appleton equation from the numerical solutions becomes obvious when the electron-neutral collision frequency is small and electron density has great spatial gradient,so the WKB approximation is not suitable to describe the wave propagation in a plasma or other media with steep density profiles.The second part is on the experimental study of the ion energy distribution function (IEDF) in low-pressure capacitively coupled plasma (CCP) system.First, the power matching network is designed by using the Smith Chart and the conclusion is that the adjustable serial capacitor depends mainly on the equivalent reactance of the discharge and the adjustable shunt capacitor depends mainly on the equivalent resistance of the discharge. The equivalent impedance is deduced from the equivalent circuits of the discharge system with different frequencies and then we find that the power efficiency (or power absorbed by the plasma) decreases with frequency. And the chamber is capacitive at low frequency and become inductive at very high frequency. Second, it is possible to have a negative self-bias voltage between the two electrodes due to the unsymmetrical configuration of the chamber, though the area of ground electrode is less than the driven electrode. And the mode transition such as plasma leak through hole can be observed easily by the abrupt change of self-bias voltage.The experiments focus on the measurement of IEDF. The conclusions are:1) The ion flux is determined by the power delivered into electrons and the effective collisional energy loss of electrons for creating a pair of electron-ion. The energy absorbed by electrons increases with driving frequency, voltage between the two electrodes and pressure, however, the effective collisional energy loss of electrons is quite different due to the change of electron energy distribution function and chemical reactions in plasma under various discharge conditions. As a result, the ion flux changes with these conditions in a complicated way.2) At constant RF voltage, the IEDF in Ar plasmas are measured with different driving frequencies and the ion flux dependence on frequency is obtained. The variations of average ion energy, energy spread and the average sheath thickness with frequency and pressure are presented.3) At constant RF power, the IEDF in O2 plasmas are measured with different driving frequencies and the ion flux dependence on frequency is obtained. The variations of average ion energy, energy spread and the average sheath thickness with frequency and power are presented.4) The electron collisional energy loss is estimated and the different electrons behaviors are speculated under various discharge conditions. According to the electron energy loss, the mode transition is suggested to be caused by the change of heating processes (from stochastic dominant toγmode).