Tyshchenko M. Propagation of Alfven waves and energy transfer across magnetic surfaces in toroidal plasmas.

This dissertation consists of the results of theoretical investigation of physics of the transverse energy transfer by Alfven waves and magnetic islands, and of effects of the spatial chanelling of the energy of energetic ions/alpha particles by destabilized Alfven eigenmodes in tokamaks. It is demonstrated that toroidicity can result in linear transformations of propagating kinetic Alfven waves into other kinetic Alfven waves branches, which differ by their mode numbers from the initial waves. Analytical expressions for the amplitudes of the transformed and non-transformed waves are derived. The transformation is found to be strong for kinetic Alfven waves with low poloidal mode numbers in typical tokamaks, NSTX (USA) and ITER (France). The magnitude and location of the particle and energy fluxes caused by the bucket motion due to the collisional slowing down of fast ions in the case of quasi-steady-state perturbations are found. Physics of the transverse energy transfer by ideal Alfven waves in toroidal plasmas is elucidated. It is found that, in contrast to the classical Alfven waves in infinite plasmas, the Alfven waves in toroidal systems produce plasma compression due to coupling with fast magnetoacoustic waves, which provides the energy transfer. The radial group velocities of the traveling waves constituting the Global Alfven Eigenmodes and Toroidicity-induced Alfven Eigenmodes are calculated. The conditions are established when multiple Alfven eigenmodes are able to withdraw a significant part of the energy of fast ions for possible transfer to another spatial region. It is calculated that about 10 GAE modes (spectrograms of instabilities in NSTX show that such a number of unstable modes are observed simultaneously) are sufficient to extract a half of the fast ion energy. It is found that spatial channeling may have played a role in the improved confinement and increased ion temperature in JET (Unite Kingdom) experiments with alpha particle heating.