Simultaneous detection of Rayleigh and Thomson scattering signals from a hollow cathode arc plasma

Electron density and temperature and neutral particle densities are simultaneously measured by evaluating 90 degrees Thomson scatter signals from electrons with superimposed Rayleigh signals from neutral particles. As a plasma source a low pressure (1 Pa) magnetized hollow cathode arc is used. The scatter volume amounts 1.5 mm3 and the detection sensitivity of the experiment reaches 109 electrons. This high sensitivity is made possible by applying a periodically pulsed Nd-YAG-laser as scatter light source in connection with a photon counting multichannel detection system. The spatial distribution of the electronic density and temperature and the neutral particle density over the discharge are reported. Based on these data the plasma scrape-off effect of the anode and the development of an anode fall is discussed.