Numerical Gyrokinetic Simulation Of Electrostatic Turbulence In Tokamak

Understanding the physical mechanism of turbulent transport is one of the key issues for the successful realization of magnetic confinement fusion power generation in tokamak.Turbulent transport simulation using gyrokinetic code is an important and powerful method for the research of controlled fusion.In the process of numerical gyrokinetic simulation research,the real experimental conditions should be restored as much as possible.Thus the kinetic effects of electrons,equilibrium flow and the multiscale characteristics,the highly nonlinearity and non-locaity of transport in tokamaks should be included in the gyrokinetic code to make the simulation results can reflect the physical mechanism of turbulent transport more truly,accurately and comprehensively.In this thesis,a new numerical method,named 'time diffusion method',for kinetic electrons has been developed to solve the numerical instability of high frequency electrostatic Alfven wave(or '?H ' mode)introduced by kinetic electrons in gyrokinetic code and successfully implemented in gyrokinetic code NLT.The time diffusion method is validated by theoretical analysis of the dispersion relation of the electrostatic shear Alfven wave after introducing time diffusion term,using the time-diffusion method to simulate the instability of linear ITG/TEM drift wave.The results show that the timediffusion method can effectively solve the numerical problems caused by the high frequency ?H pseudo-mode,significantly increase the time step of numerical simulation,and improve the computational efficiency.In addition,this algorithm has almost no additional computational cost while retaining the complete kinetic effects of electrons.At the same time,in order to accurately simulate the dispersion relation of drift wave at short wavelength,especially for electron drift wave,we develop a matrix gyro-average operator and a matrix double-gyro-average operator based on toroidal spectral decomposition and an arbitrary wavelength solver based on them for NLT.Based on this algorithm,the nonlinear evolution of microturbulence driven by ITG/TEM instability in tokamak was simulated.By comparing the adiabatic and nonadiabatic electron cases of ITG-dominated drift wave turbulence,it is found that the kinetic effects of electrons have a destabilizing effect on the micro-turbulence,which increases the turbulence saturation amplitude and transport level of the turbulence.It is found that the heat transport of ion and electron are decoupled in ITG-dominated drift wave turbulence and the particles transport inward.In TEM-dominated drift wave turbulence,ion and electron heat transport are coupled and the particles are transported outwards.The above non-linear turbulence simulation further verifies the accuracy and validity of the kinetic electron model in NLT.Finally,the plasma toroidal rotation for the nonlocal gyrokinetic code NLT based on the gyrokinetic equationunder the laboratory framework[1].Then the NLT is used to study the influence of the plasma toroidal rotation on the zonal flow,including the influence of the toroidal rotation on the amplitude of RZFs,the influence on the frequency and damping rate of GAM.The results are verified with the analytical theory,and the physical mechanism of the influence of the equilibrium flow on the zonal flow is explained numerically.At the same time,in the simulation process,it is found that the toroidal rotation of plasma has an enhanced effect on the cos ? component of GAM.In analytical models that do not contain plasma rotation,this term is generally considered negligible.Through the qualitative theoretical analysis under the condition of small toroidal rotation speed,we point out that the enhancement of the cos ? component of the model is mainly to respond to the polarization density cos ? component caused by the toroidal rotation to meet the quasi-neutral condition.