Energetic Particle driven Alfven eigenmodes in KSTAR plasmas

Abstract

In tokamak plasma, energetic particles (EP) generated by the external heating systems or the fusion reactions can lead to the excitation of global instabilities. Alfven eigenmodes (AEs) are such modes that destabilized via inverse Landau damping, when their EP drive exceeds the total damping, and can degrade the fast ion confinement and, thus, the self-heating. Furthermore, these fast particles can cause the severe damage to the reactor wall. So understanding the stability properties and their induced fast ions losses of such AEs are essential for any future fusion devices.

We have presented the detailed study of Alfven eigenmode in tokamak plasmas, with the help of simulations and experimental results for the KSTAR tokamak. This dissertation is divided into two parts, in first part we have presented our study on the AEs based on theory and numerical simulations. For the theory we have focused on the physics of Alfven Eigenmodes and their excitation based on three type of approaches including the MHD, the reduced kinetic-MHD model and the gyrokinetic model. Where for the numerical study based on MHD and reduced kinetic-MHD model we have developed the eigenvalue code, Kinetic Alfven Eigenmodes Solver (KAES), to study the characteristics of AEs (more specifically toroidicity induced Alfven eigenmodes (TAEs) and beta-induced Alfven eigenmodes (BAEs)) and their damping and energetic particle drive characteristics. In this part we have also presented our results for the radially trapped AEs which are formed due to the coupling of AEs and the kinetic Alfven waves (KAWs). In the second part of the thesis we have focused on the more realistic tokamak plasmas (with general geometry and realistic plasma equilibrium), like KSTAR equilibrium. We presented the experimental observation and particle-in-cell (PIC) simulations of the TAEs destabilized by the NBI's driven fast particles and their characteristics found in KSTAR tokamak. We have found the simultaneous excitation of multiple discrete TAEs for a single toroidal mode number observed in KSTAR plasmas. The excitation and characteristics of these modes are studied by using a global gyrokinetic particle-in-cell simulation code which agrees well with the experimental observation. It is shown that compared to a single core localized mode, the excitation of multiple modes is difficult. Moreover we have also presented the effect of AEs on the phase space dynamics and particle transport in tokamak.

This thesis provides the detailed physics understanding of the Alfvenic instabilities, from the theoretical aspects to the experimental observations, and from the linear characteristics to the phase space dynamics of the Alfven eigenmodes.