Gyrokinetic Simulation Of Ion Temperature Gradient Modes In Internal Transport Barriers

Tokamak is the most potential devices for human beings to achieve controlled nuclear fusion.At present,there are still a series of physical and engineering problems that need to be solved urgently.The internal transport barrier（ITB）is a special tokamak physical phenomenon,which produces the parameters beneficial to improving confinement of plasma and improving device performance.The confinement of plasma is strongly related to transport.In-depth research on the transport characteristics of plasma in ITB can provide guidance for the design and operation of future fusion reactors.The turbulence generated by the micro-instability driven by the ion temperature gradient（ITG）is the most important physical mechanism that triggers the ion heat transport in the core of the tokamak.In this paper,with the ITB experimental data of the HL-2A device,the gyrokinetic code GKV+ is used to analyze the characteristics of ITG in ITB,which is beneficial to the exploration the physical mechanism of transport in ITB.The thesis first briefly introduces the principle of magnetic confinement fusion,and reviews the tokamak device and its plasma confinement and transport issues.Secondly,the theory of tokamak ion temperature gradient（ITG）instability is introduced.The characteristics of the internal transport barrier（ITB）and the current experiments and theories of the internal transport barrier are reviewed,which indicates the basic characteristic that ITG in ITB is instable.Based on it,the HL-2A device and its typical ITB discharge experimental phenomenon are introduced and analyzed.In third chapter of the thesis,the theoretical model and basic equation of gyrokinetic kinetics used in this work are introduced,as well as the corresponding numerical simulation program,GKV+ code.In the fourth chapter of the thesis,the basic calculation example（CBC）parameters are firstly used to analyze ITG linear instability with different kinetic codes.The calculation results of different codes are compared,and the applicability of GKV+ in this type of problem is verifies.Then the effects of ion-electron temperature ratio and magnetic shear on ITG growth rate and critical ion temperature gradient are analyzed and studied.In the fifth chapter of the paper,based on the ITB experimental data of the HL-2A device,the GKV+ code is used to simulate and calculate the properties of the linear instability in ITB region during the ITB formation.The typical ITG instability characteristics in the most unstable mode’s structure（shown by potential fluctuation）density fluctuation distribution,parallel velocity fluctuation distribution,pressure fluctuation distribution in two directions and parallel heat flow fluctuation distribution in two directions are obtained.This indicates that the turbulent transport caused by ITG-driven micro-instability is an important physical mechanism in the formation of internal transport barriers is.At the end of the thesis,the research results obtained at present are summarize.The problems that need to be improved in the research work and the content to be carried out in the next step are analyzed.