2-DIMENSIONAL ION VELOCITY DISTRIBUTION-FUNCTIONS IN ELECTRON-CYCLOTRON-RESONANCE PLASMA UNDER A DIVERGENT MAGNETIC-FIELD

Two-dimensional ion velocity distribution functions are measured in el ectron cyclotron resonance (ECR) argon plasmas under a divergent magne tic field configuration using a directional analyzer. Ions produced in the ECR source grow to a beam in the downstream region inside an allo wed angle, while the distribution function is almost isotropic outside the angle. The beam energy corresponds to the potential difference be tween the ECR source and downstream locations. The ion beam is almost parallel to an applied magnetic field, the beam being deflected along the divergent magnetic field lines. The energy spread and the temperat ure of the ion beam, and the temperature of the bulk ions are also sho wn as a function of the distance from the ECR source or of the gas pre ssure. The validity of the directional analyzer measurements is discus sed by considering the motion of an ion in a sheath in front of the an alyzer.