Étude spectroscopique des phénomènes de résonance dans les plasmas micro-ondes
In plasmas produced by high-frequency electromagnetic fields, electron heating can result from ohmic heating (collisional) or from collisionless processes. In this regime, the production of suprathermal electrons can result from the conversion at the resonant point (when the plasma permittivity εp→0) of the propagating electromagnetic wave into electrostatic waves and their absorption by Landau damping. The objective of this Master's thesis is to experimentally characterize the effect of collisionless processes associated with the presence of resonance phenomena on the electron energy distribution function (EEDF). The study was carried out by trace-rare-gases optical emission spectroscopy (TRG-OES) in various plasmas capable of exhibiting resonance phenomena. For low-pressure tubular plasmas (< 50 mTorr) produced by an electromagnetic surface wave at 600 MHz, EEDF is characterized by two temperatures: TeAldescribes the mean energy and TeTail represents the high-energy tail of the distribution. A parametrical study of these temperatures as a function of the axial distance and the gas pressure revealed that the ratio TeTail / TeAlincreases with the characteristic length of the electron density gradient L. Similar measurements and analyses were also performed in a magnetized microwave plasma source sustained at the electron cyclotron resonance. In such conditions, the production of suprathermal electrons results not only from the resonance phenomena and wave-particle interactions mentioned above but also from the electron cyclotron resonance
Plasma produced by microwave fields optical emission spectroscopy wave-particle interactions resonance phenomenon