Collective scattering spectra with anisotropic distribution of fast ions

Collective Thomson scattering (CTS), a promising diagnostic for fusion plasmas now made feasible by the availability of high-power gyrotrons in the millimeter wavelength range (COSTLEY et al., 1988, JET Report R(88)08, Abingdon, Oxon), is known to be particularly sensitive to the presence of fast-ion populations in the plasma. In this paper we investigate the effects on CTS spectra of the anisotropies often involved in the production, heating, confinement and slowing down of these energetic populations in a fusion device. Two kinds of velocity-space anisotropies are considered: (a) that associated with the transfer of energy from an external source to a reduced number of degrees of freedom (e.g. perpendicular acceleration of ions during ICRH), and (b) that associated with transverse particle losses due either to orbits intersecting the walls or to magnetic field ripples. Numerical computations of the CTS spectra have been performed for the relevant cases and a number of features characterizing the plasma behaviour in the presence of suprathermal-ion populations, typically the enhancement of the fluctuation level at the lower hybrid resonance, are quantified analytically.