Numerical Investigation On Neoclassical Toroidal Viscosity Torque And The Resulting Plasma Steady State Rotation In Tokamaks

Effective control of edge localized mode(ELM)is a necessary condition for accomplishing high-performance tokamak operation.Resonant magnetic perturbation(RMP)field is capable of suppressing ELM and is one of the important methods in improving tokamak plasma performance,thus it is widely used in most of the tokamaks including ITER.Because of the existence of RMP field,and the unavoidable error field and plasma instabilities,magnetic field in tokamaks is usually non-axisymmetric.Neoclassical toroidal viscosity(NTV)effect is a common physical phenomenon in general three-dimensional magnetic field configuration,the induced NTV torque can significantly influence the plasma toroidal rotation,hence change plasma instabilities and confinement.NTV torque is also expected to be an efficient method in driving plasma rotation for low torque injection plasma like ITER.Investigation on NTV torque and the resulting plasma steady state rotation deepens the understanding of three-dimensional magnetic field physics,provides physical foundation for design of plasma rotation control strategy in tokamak experiments,and is of great significance for rotation driving and optimization for future fusion reactors(e.g.ITER).This dissertation is on the numerical modeling of NTV torque and the resulting plasma steady state rotation,including the following aspects:1.By solving the mismatches between NTV torque calculation code NTVTOK and parallel nonlinear MHD code NIMROD with regard to coordinate choice,data storage,and physical quantity definitions,a coupling calculation module between these two codes is newly developed and successfully applied in the calculation of RMP induced NTV torque in realistic tokamak configurations.Under the reasonable plasma parameter condition.RMP induced NTV torque can reach the same magnitude as other commonly used toroidal momentum sources,e.g.NBI(Neutral Beam Injection)induced torque,indicating the capability of RMP induced NTV torque on influencing or governing plasma rotation.The development of such a coupling module enriches parameter input of NTVTOK code,extends the research area of NIMROD code from pure MHD process to the processes including neoclassical transport,and provides the foundation of NTV torque modeling for various scenarios;2.Neoclassical offset rotation based on DIII-D experiments is calculated and analyzed.The obtained neoclassical offset rotation in counter-Ip direction is in the same order of magnitude as DIII-D experimental results,and bounce-drift resonance,collisionality,magnetic perturbation spectrum can influence the existence of co-Ip neoclassical offset rotation.Based on the modeling results,we proposed the methods of adjusting electron temperature and tuning magnetic perturbation spectrum,which can be possibly adopted in experimental rotation control and optimization.Especially,we innovatively pointed out the effects of magnetic perturbation spectrum on the existence of co-Ip neoclassical offset rotation,and revealed the corresponding physical mechanism;3.The study of neoclassical offset rotation is extended from two aspects:Firstly,neoclassical offset rotation based on ITER configuration is calculated and analyzed.It is found that the change of magnetic perturbation spectrum is still capable of affecting neoclassical offset rotation for ITER scenario.Therefore,the idea of utilizing the effect of magnetic perturbation spectrum in plasma rotation control is not only applicable for DIII-D,but also expected to contribute for ITER plasma rotation optimization;Secondly,under the circumstance of multiple toroidal momentum sources,based on simple tokamak configuration with circular cross section and simplified momentum transport equation,the total plasma steady state rotation is calculated and analyzed.When NTV torque and other momentum sources act on plasma together,steady state rotation varies towards neoclassical offset rotation when magnetic perturbation becomes larger,which is qualitatively consistent with plasma steady state rotation measured in KSTAR experiments.The contribution of trapped electron is a key issue in determining plasma steady state rotation.The research in this dissertation includes a new coupling between NIMROD and NTVTOK codes for NTV torque computation,deepens the understanding of plasma steady state rotation under the influence of NTV torque,and explores the possibility of controlling plasma rotation using RMP induced NTV torque.The modeling results provide theoretical ideas for experimental rotation control,contain theoretical significance for rotation control and optimization for future fusion reactors like ITER.