ALPHA-PARTICLE DETECTION BY ELECTROMAGNETIC SCATTERING OFF OF PLASMA FLUCTUATIONS

A code has been developed which calculates the differential cross-section for the scattering of incident gyrotron radiation off of thermal fluctuations in a warm, weakly inhomogeneous magnetized plasma. The model is derived from the linearized Vlasov-Maxwell equations by retaining all electromagnetic field fluctuations in addition to the usual electron density fluctuations. Alpha particles are modelled using a slowing down distribution with a birth energy of 3.5 MeV, while a (bi-) Maxwellian is used for the background plasma. Illustrative results for parameters appropriate to TFTR and JET are presented. Different cases are compared by plotting the ratio of scattered power to incident power as a function of frequency, and the dispersion relation for the incident and scattered radiation (X or O mode) is enforced at every point. Cases for which the scattering is dominated by electromagnetic field fluctuations are presented, and the role of the (electromagnetic) lower hybrid resonance as an amplifier of the alpha particle signal is made apparent.