Far-forward scattering observations of an Alfven wave experiment

Far-forward scattering of submillimetre laser radiation has been used to detect the density fluctuations associated with the discrete Alfven wave and kinetic Alfven wave resonances in an Alfven wave experiment on the TORTUS tokamak. With the aid of calculations, in which interaction of the radiation with the waves is described in terms of diffraction by a phase grating representation of the plasma density fluctuations, it has been possible to distinguish unambiguously between the two resonance conditions. This was not possible, in the present experiment, using magnetic probe diagnostics alone. (Author)