OPTICAL MIXING BASED CONFINED ALPHA-PARTICLE DIAGNOSTIC

A method for probing the confined alpha particle velocity distribution function in a fusion plasma by exciting and scattering from a lower h ybrid wave is described. Two microwave sources propagating perpendicul ar to the magnetic field optically mix inside the plasma, and the freq uency of one of the sources is swept such that their difference freque ncy passes through a lower hybrid resonance. A third microwave source propagating antiparallel to one of the mixing sources scatters from th is excited beat wave with the scattered radiation propagating antipara llel to the other mixing source. Thus, the scattered signal power can be easily recovered and used to reconstruct the alpha particle distrib ution function since the width of the detected resonance is proportion al to the slope of the alpha distribution function. (C) 1997 American Institute of Physics.