Test Particle Simulation Of Alpha Particle Loss Induced By Toroidal Field Ripple

Alpha particles generated by D-T fusion will be the main heating source for the future advanced tokamaks.It is essential for us to understand the physics of burning plasmas by investigating the transport and loss mechanisms for α particles.In a real tokamak reactor,due to the discreteness of toroidal field(TF)coils,there will be a kind of periodical magnetic perturbation adding on the equilibrium magnetic field,which is called TF ripple.According to previous researches,the plasma confinement will decrease because the TF ripple destroys the axisymmetry of the magnetic field.In future reactors,fusion energy gain factor will usually be greater than 10,which means that the α particles are a main heating source,accounting for a large fraction of heating.Therefore,a small loss fraction of α particles induced by any kind of reason will cause a large impact on the first wall.In order to decrease the negative effects of loss particles on the devices,we should study the mechanisms of α particle loss and transport at the present stage using the numerical method.The test particle method is a good way to studyα particle loss and transport,which is realized by tracking particle trajectories.China Fusion Engineering Test Reactor(CFETR)is now in the period of physics and engineering design and will be the next fusion device in China.In this master’s degree thesis,we use the test particle method to study the confinement and loss of α particles influenced by TF ripple in CFETR.The thesis is organized as follows:In part 1,we introduce the background of magnetically confined fusion and the generation and the loss of energetic particles.A review of the energetic particle loss induced by the TF ripple is given.In part 2,the Lorentz orbit equations and the guiding center orbit equations are presented,which are two common equations in the guiding center method.Also,the numerical code ORBIT used in this thesis is introduced,including the diagram,functions,and the input and output of the code.In part 3,based on the guiding center code ORBIT,we study the α particle TF ripple loss in CFETR steady-state scenario.Considering two kinds of distribution,namely the initial distribution and the steady-state slowing down distribution,we calculate the particle loss fractions,loss mechanisms,and the heat load on the first wall.It shows that the stochastic ripple diffusion is the main loss mechanism in CFETR steady-state scenario;compared with the results in CFETR hybrid scenario,the ripple loss phenomenon in the steady-state scenario is more striking.In part 4,we introduce a brand-new test particle code,PTC,which is developed by researchers in Dalian University of Technology.A brief introduction of the background and the diagram of the code is given.The main part of this section is the benchmark work done by PTC and ORBIT,comparing the orbit in both the equilibrium field and in the TF ripple.Also,the slowing down and scattering effect by collision are tested by com paring the analytical results.Finally,a summary and an outlook of this work are given.