ION VELOCITY DISTRIBUTION FUNCTION OBSERVATIONS IN A MULTIPOLAR ARGON DISCHARGE

Observations of ion velocity distribution functions in two different configurations of a multipolar device with a laser induced fluorescence diagnostic in argon plasma are presented. The first experiment, carried out in the magnetic field closing the two ends of the device, shows the influence of this field on the ion trajectories. In the second experiment performed without the magnetic field closing the two ends of the device, the influence of the electrostatic boundary potential of the plasma is observed. Longitudinal ion velocity distribution functions have been recorded until inside the plasma sheath. The shapes of these distribution functions are in qualitative agreement with the results of a theoretical model and give an experimental justification for the "flux" shape of the ion velocity distribution source function retained in this model. However, to reach this qualitative agreement, it is necessary to adjust the ionic temperature for each distribution function suggesting that, for the authors' weakly ionized plasma, another heating mechanism is missing in this theory. © 1995 American Institute of Physics.