Numerical Investigation Of Electromagnetic Instabilities In Tokamak Plasmas

Various electromagnetic instabilities involving magnetic and current fluctuations in Tokamak,e.g.,drift instabilities and Alfven instabilities,are of great importance for the plasma boundary stability and energetic particle physics,which are essential for H-mode pedestal and burning plasmas.The kinetic ballooning mode(KBM),an electromagnetic drift instability,can be easily excited by the steep pressure profile in the tokamak pedestal.The pressure gradient threshold of KBM plays a crucial role in the EPED model,which has successfully predicted pedestal height and width in the H-mode discharges of many tokamaks.Alfven instability is another kind of important instability,including beta-induced Alfven eigenmodes(BAE),toroidicity-induced Alfven eigenmode(TAE)and et al,which can be destabilized by energetic particles(EPs)through transition resonance or precession resonance.KBM,as a drift Alfven instability,can be strongly coupled with BAE with the presence of large ion temperature gradient to make BAE the most unstable branch.These electromagnetic instability driven modes.can cause a large resonant EP loss even with low amplitude of magnetic fluctuations,which will severely damage the first wall facing the energy and momentum fluxes of EPs.In the thesis,we use and develop novel numerical tools to investigate the linear physics of KBM and Alfven instabilities for tokamak plasmas in the following three aspects.(1)We use global gyrokinetic code GTC to find the physical mechanism for the sensitivity of KBM instability to plasma equilibrium configuration.It is found by the GTC linear simulation that when the flat temperature and density gradient profiles are used,the radial mode structure shifts outward under positive magnetic shear.By proposing and solving a simplified theoretical model for KBM,we find that the outward shift of the KBM mode structure is due to the parallel ion compressiblity,which provides stabilization for KBM under positive magnetic shear and has no effect under negative magnetic shear.This is further verified by the GTC simulation results with positive and magnetic shears.(2)We have independently developed the Drift Alfven Energetic Particle Stability(DAEPS)code,a comprehensive non-perturbative linear instability code,to investigate various drift Alfven modes observed in tokamak plasmas.The advantage of the DAEPS code is that it can calculate fast and efficiently self-consistently not only the frequency,growth rate,and the mode structure of the drift Alfven instability,but also the asymptotic behavior which can be compared to the theory.Since the DAEPS model equation automatically satisfies the General Fishbone-like Dispersion Relation(GFLDR),therefore,the DAEPS code can be conveniently used to analyze the interaction physics between the particle dynamics and drift Alfven instability.(3)We use the DAEPS code to study the BAE and TAE physics dominated by circulating particle dynamics.A reduced kinetic compression term is implemented for modes with long wavelength,like BAE and KBM,which can accelerate the calculation speed hundreds of times faster without losing accuracy.The DAEPS result suggests that the parallel electric field,ignored in the DAEPS model equation,affects little the BAE instability;it also suggests that finite Larmor radius(FLR)and finite orbit width(FOW)effects can stabilize the BAE and TAE modes by suppressing the wave-particle resonance.