ACTIVE BEAM PROBE SPECTROSCOPY, A PROPOSAL OF MEASURING INTERNAL MAGNETIC-FIELD DISTRIBUTION

For the study of magnetically confined plasmas, it is important to mea sure the q profile in tokamaks as well. as the change of magnetic fiel d configuration caused by the high beta effect in helical systems. The motional Stark effect has recently been utilized to find out the dire ction of local magnetic field by measuring the direction of polarizati on of spectral line emission from injected beam particles. The present proposal is to improve the spatial resolution and the accuracy of thi s method by combining a technique of laser spectroscopy with it. A lin early polarized laser beam will be injected coaxilly with the neutral particle beam. Phase sensitive detection of induced fluorescence from the polarization-modulated laser light tuned to a split spectral line will be used to detect the local magnetic field direction, instead of observing the polarization of emissions due to electron impact excitat ion of injected atoms. An experimental scheme proposed and characteris tics estimated will be described.