POTENTIAL AND VELOCITY-MEASUREMENTS IN A MAGNETIZED HOLLOW-CATHODE DISCHARGE BY MEANS OF ELECTRIC PROBES AND LASER-INDUCED FLUORESCENCE

By means of electric probes, surfaces of equal electrical potential are measured in the plasma of a magnetized hollow cathode arc burning in argon. At moderate distances between the cathode and the anode the potential increases nearly linearly in proceeding in the axial direction from the cathode to the anode. In the radial direction a potential growth can be observed up to a plateau regime near the plasma edge. If the cathode-anode distance exceeds a critical length, the situation changes insofar as a voltage jump of nearly a factor of 2 occurs near the anode where higher voltage values are reached than on the anode surface. There the voltage drops in the radial direction to the outside plateau value. This voltage distribution is produced by a (positive) anodic space charge cloud, which accelerates the electrons. The voltage jump guarantees the transport of the arc current even in the case of a long arc. This space charge decelerates the ions flying in the axial direction and creates the possibility of ions rotating around the cathode-anode axis in the anode regime. This latter possibility was examined by monitoring the frequency resolved Doppler shift of the argon ion line at λ=611.49 nm measured by laser induced scattering. The flow field of the ions can be quantitatively understood from the spatial distribution of the electrical potential. © 1988 American Institute of Physics.