Tykhyy A. Wave processes and transport of suprathermal ions in quasi-isodynamic stellarators

This dissertation consists of the results of theorerical investigation of diffusional transport of suprathermal ions in stellarators, particularly in optimized (quasi-isodynamic) stellarators of the Wendelstein type, of the conditions of destabilization and damping of Alfven eigenmodes in such stellarators, and of the energy flux across magnetic field surfaces associated with such instabilities. A consistent theory of stochastic diffusion of suprathermal ions is derived. It is shown that stochastic diffusion in Wendelstein-type stellarators is several times stronger than previously predicted. A method of mitigation of stochastic diffusion losses is proposed that is based on closing the separatrices between locally passing and locally trapped orbits within the plasma volume, and the influence of radial electric field on the confinement of locally trapped suprathermal ions in stellarators is studied. The use of a resonance radial electric field is proposed for helium ash removal in the Helias reactor. The strong stabilizing influence of the Landau damping mechanism on Alfven eigenmodes in stellarators due to the presence of non-axisymmetric resonances is demonstrated. It is shown that isomon and toroidicity-induced Alfven eigenmodes are unlikely to be destabilized in the first NBI experiments on Wendelstein 7-X. It is shown that Alfven eigenmodes may be destabilized by temperature gradient of the bulk plasma ions, and that this destabilization is accompanied by an energy flux across the magnetic field. In Wendelstein 7-X, this mechanism may lead to a destabilization of an Alfven mode with frequency ~200kHz, which may explain long-lasting high-frequency oscillations observed in experiments.