LOW-ENERGETIC HE-ATOM BEAM AS A DIAGNOSTIC PROBE FOR ELECTRIC-FIELD MEASUREMENT IN THE PLASMA EDGES

Two types of low-energetic He-atom beam sources were constructed for d irect measurement of electric field distribution in tokamak plasma edg e region with aid of laser-induced fluorescence (LIF) technique. One i s a continuous plasma flow extracted from an electron cyclotron resona nce (ECR) plasma source. The plasma parameters were measured by Langmu ir probes, while density profiles and velocity of metastable He atoms (2(1)S) in the plasma flow were measured by LIF methods. It was found that extremely high density metastable atoms of similar to 10(11) cm(- 3) were created at 7 cm apart from the outlet of the source. Formation mechanism of such high density 2(1)S atoms was briefly discussed on t he basis of atomic processes. Another is a pulsed free jet having a pa ir of discharge electrodes to produce the 2(1)S atoms in the jet. High density 2(1)S atoms(similar to 10(10) cm(-3)) were found to be create d in the discharged jet by means of the optical absorption method.