Hybrid Simulation Of Toroidal Alfvén Eigenmode And Fishbone-Like Mode In Tokamak

Understanding of energetic particle physics issue in tokamak is of significant importance for the achievement of steady-state long pulse operations in the future fusion reactors.In the future burning plasmas,the self-heating is provided by the 3.5 MeV ? particles produced by the deuterium-tritium fusion reaction.Furthermore,other high-power auxiliary heating methods,such as neutral beam injection and radio frequency wave,will be employed in the future fusion reactors and will generate a large amount of energetic particles.On one hand,these energetic particles can destabilize various instabilities via wave-particle resonance interaction;on the other hand,these destabilized instabilities can cause the radial transport,significant loss and redistribution of energetic particles,leading to the decrement of plasma confinement and the destruction of the first wall.It is,therefore,a vital research topic to better understand the loss mechanisms and accurately assess the loss fraction of energetic particles.There are two main kinds of instabilities driven by energetic particles.One is Alfvén eigenmode,such as toroidal Alfven eigenmode(TAE)and the other one is energetic particle mode,such as fishbone-like mode(FLM).TAE,especially multiple toroidal mode number TAE(multiple-n TAE),is considered as one of the main reasons of energetic particle loss in the International Thermonuclear Experimental Reactor(ITER)because of its global mode structure.Under the suitable conditions,TAE avalanches resulted from the simultaneous evolution of multiple-n TAEs will significantly enhance the transport and loss of energetic particles,which is a badly harmful event for the steady-state operation of future tokamaks.So far,TAE avalanche has been observed in many tokamak devices,such as National Spherical Torus Experiment(NSTX).However,the understanding of physics mechanism of TAE avalanche has been understood very limited.Thus,it is very essential to perform self-consistent multiple-n simulations using realistic experimental parameters and profiles.In addition,in order to explain the recent observation of FLM resulted from the resonant interaction between tearing modes and energetic-ions on HL-2A,the corresponding massive simulation is performed.In this thesis,the main research contents are as follows.In chapter 1,the research background and the aim of this thesis are introduced,and the research progress of TAE,TAE avalanche and the FLM resulted from the interaction between energetic-ions and tearing modes are mainly summarized.Finally,the main research contents of this thesis are presented.In chapter 2,the massively parallel kinetic/MHD hybrid code M3D-K used in this thesis is introduced,including the physical models and numerical methods.In the code,a threedimension extended MHD model was used to describe the thermal plasmas and a kinetic model was employed to describe the energetic-ions injected by the neutral beam injection.In chapter 3,the nonlinear evolution of multiple-n TAEs driven by energetic-ions and the energetic-ion losses induced by them are self-consistently investigated by M3D-K code.To clearly identify the effect of nonlinear mode coupling on the energetic-ion loss,simulations over single-n modes are first carried out and the frequency chirping,wave-ion resonance,trajectory of lost energetic-ions in phase space and the effect of injection speed on energetic-ion loss are analysed in detail.It is found that the energetic-ion loss level increases with the increment of injection speed of energetic-ion.This is mainly due to the fact that the larger injection speed renders the wider orbit width,leading to the stronger anomalous transport and higher energetic-ion loss.In the single-n TAE simulation,the mode's growth and chirping can induce island broadening and drift.When the saturated island moves outwards and interacts with the loss boundary,the energetic-ion may pass the last closed flux surface.This is the main loss mechanism in the single-n TAE.In the multiple-n TAE simulation,it is found that the resonance overlap occurs so that the energetic-ion loss level is rather higher than the sum loss level that represents the summation of loss over all single-n modes.Moreover,increasing fast ion beta ?h can not only significantly increase the loss level in the multiple-n TAEs but also largely enhance the loss level difference between the single-n and multiple-n cases.This is mainly due to the fact that the increment of energetic-ion beta can result in the stronger resonance overlap.In addition,the characterization of lost energetic-ions in E-?? phase space is obtained in both single-n and multiple-n cases.It is found that trapped energetic-ions are dominant among the energetic-ion losses and most of them transfer energy to the wave.In chapter 4,based on the experimental observation of TAE avalanches in shot 141711 on NSTX,a self-consistent multiple-mode simulation associated with TAE avalanches is performed using the experimental parameters and profiles at the time slice of t=471 ms before the occurrence of TAE avalanche as the M3D-K input.The mode-mode coupling among different components and the resonant interaction between different components and energetic ions during TAE avalanches are identified in the simulations.It is found that the effective mode coupling and a sufficiently strong drive are two important ingredients for the onset of TAE avalanches.TAE avalanche is considered to be a strongly nonlinear process and it is always accompanied by the simultaneous rapid down-chirping of frequency of multiple modes and significant energetic-ion losses.The experimental phenomenon is also observed on NSTX and is reproduced by the simulation results in this chapter.In chapter 5,based on the observation that an m/n=2/1 unstable tearing mode interacts with energetic-ions,resulting in frequency-chirping fishbone-like activities,a detailed study of global nonlinear hybrid kinetic/MHD simulations with M3D-K code is performed.It is found that the co-passing energetic-ions play a dominant role in the wave-ion resonances and the corresponding resonance condition is ?t+2?p=?,where ?t,?p,? are the toroidal motion frequency,the poloidal motion frequency and the mode frequency respectively.The kinetic effect of co-passing energetic-ions from non-adiabatic response is interestingly found to be strongly destabilizing while the net effect with both adiabatic and non-adiabatic contributions is weakly destabilizing.In this chapter,effects of energetic-ion beta ?h and pinch angle ?0 determining different energetic-ion fractions on the resonance features are also discussed in detail.The relevant simulation results are consistent with the observations on HL-2A.In addition,significant redistribution and loss induced by the resonant interaction between tearing mode and energeticions are clearly observed in multiple-mode simulations,and the scaling of energetic-ion loss fraction with the fluctuation amplitude is found to be floss ?(?),indicating that the loss is convective.These discoveries are conducive to understanding the mechanisms of tearing mode induced energetic-ion loss through the resonant interaction.In chapter 6,a summary of the research results for this thesis is given and the innovation points of this thesis are listed.Finally,the prospects of future research work are presented.