Formation of the electron velocity distribution in an ECR plasma

Theoretical discussion is made of the electron velocity distribution in an ECR (electron cyclotron resonance) plasma formed and heated in a mirror field. The basic mechanism of the heating process is described first on the simple assumption that a vibrating field exists in the fundamental resonance region. Next, the mechanism of the diffusion and heating of electrons in the velocity space is discussed. The process of cyclotron resonance heating is discussed mathematically based on a two-dimensional random walk model. Then, the electron velocity distribution in an ECR plasma is discussed in relation to other factors which are not included in the basic assumption. Finally, currently known aspects of the electron velocity distribution in an ECR plasma are summarized. In an ECR plasma in a mirror field, the electron velocity distribution tends to become less isotropic and high-temperature electrons form more efficiently. The distribution becomes apparently isotropic in the central portion of the mirror field away from the resonance region. Velocity distribution equations for electrons in an ECR plasma in a mirror field can be evaluated detailedly through numerical analysis by means of a diffusion equation which incorporates terms expressing the loss and supply of electrons and their relaxation due to collision. (N.K.)