Characterisation of the electronic population in a plasma of electron cyclotron resonance ion source

Two approaches have been developed to characterise the electronic population of an E.C.R.I.S. (Electron Cyclotron Resonance Ion Source): Experiments have been carried out on a source dedicated to plasma studies. The electron density, the plasma potential and the diamagnetism have been measured. These experiments show that the electron distribution function (EDF) is not Maxwellian: there are not enough collisions to thermalize the rf-heated electrons, so that a large tail of hot electrons appears in the EDF. As these energetic electrons have a long confinement time, they are responsible for the highly charged ions obtained in the E.C.R.I.S. On the other hand, a theoretical approach has been undertaken to obtain the electronic distribution. This thesis develops the physical phenomena which are responsible for the evolution of the EDF: the collisions between particles, the rf quasilinear interaction between the rf-wave and the electrons, and the ionisation of the ions or the atoms of the plasma are modelled. The equation obtained is solved numerically. Calculations show saturation phenomena of the electronic density and the absorbed power, which explains the limit of the present sources. The results are in good agreement with the experimental data. This thesis confirms that the EDF is not Maxwellian. The calculations give the EDF according to parameters which depend on the geometry of the source. For the first time the ultimate density which can be obtained in an E.C.R plasma has been investigated experimentally and derived theoretically. (author)