Scattering from discrete Alfven waves in a tokamak using a gyrotron radiation source

A tunable gyrotron is used as the radiation source in a far-forward scattering experiment to investigate the density fluctuations associated with the appearance of discrete Alfven wave (DAW) resonances and kinetic Alfven waves (KAWs) in the TORTUS tokamak plasma. A new arrangement of a quasioptical antenna and a Gaussian telescope focuses the gyrotron output into the plasma. Predictions of the scattered amplitude and phase take into account the diffraction and refraction of a Gaussian beam in the plasma. The scattering experiments enable DAW resonances and KAWs to be identified, and their characteristics are in broad agreement with the predictions.