SPECTROSCOPIC METHOD TO DIRECTLY MEASURE ELECTRIC-FIELD DISTRIBUTION IN TOKAMAK PLASMA EDGE

A supersonic helium beam source operated in pulse mode was constructed for direct measurement of electric field distribution in the tokamak plasma edge region with the aid of laser-induced fluorescence (LIF) te chnique. In this technique only the polarization has to be observed of a LIF resulting from a laser-excited forbidden transition due to the Stark effect and the electric quadrupole to determine the electric fie ld strength. No calibration is needed of the absolute intensity of LIF and tunable laser used. The helium atom beam density was obtained (ab out 10(20) He atoms cm(-2) s(-1)) at a distance of 7 cm from the pulse d nozzle. A model-type experiment to make clear the influence of a mag netic field on the LIF is reported. Design study was also made to inst all the supersonic beam and spectroscopic measurement system on a medi um size tokamak. (C) 1997 American Institute of Physics.