Investigated On The Topological Structure Of Particle Orbit In Chinese First Quasi-axisymmetric Stellarator(CFQS)

The Chinese First Quasi-axisymmetric Stellarator（CFQS）is a joint project of international collaboration.It is designed and fabricated by the Southwest Jiaotong University（SWJTU）in China and the National Institute for Fusion Science（NIFS）in Japan.The target parameters of CFQS are chosen as follows:the toroidal period number N_p=2,major radius R₀=1.0 m,magnetic field strength B_t=1.0 T,and aspect ratio A_p=4.Based on the CFQS magnetic field configuration,the topological structure of particle orbits and the mutual transformation between orbits are systematically investigated,and a new physical mechanism is proposed for this phenomenon in the thesis.Firstly,the evolution equation of particle with time is derived by means of Lagrange equation in Boozer magnetic surface coordinates by Lagrangian equations of motion and Hamiltonian principles,namely,the evolution of poloidal angle,toroidal angle and magnetic flux with time.The magnetic field information for CFQS is provided by tree dimensional equilibrium VMEC code,then the particle orbit equation is studied.Second,the min value of the second adiabatic invariants J for some singular points less than other surrounding are discovered the plane ofρ-ζ_Nin CFQS.It predicts these minima J may come from the transformation and escape of the trapped particles.Therefore,Investigated on the particles with energies of 0.1ke V,1ke V,10ke V and 100ke V,the orbital transition of the trapped particles exist extensively particles of various energies.Investigated on magnetic field toroidal inhomogeneity,poloidal drift and radial drift for further research the characteristics of magnetic field configuration and particle orbit topology in CFQS,the magnetic topology is closely related to the magnetic field components,where the dominant components B_1,0,B_1,1and B_0,1.The coupling of poloidal drift and radial drift causes special loss channel of particles.Most of trapped particle have their orbits transformed and lost in the loss channel.Most of the trapped particles have their orbits transformed and lost in the loss channel.These studies provide a new direction and basis for the optimization of quasi-axisymmetric（QA）configuration with local axisymmetry-breaking.Finally,how to suppress transition and loss of trapped particles in the loss channel,and the optimization of magnetic configuration is deeply discussed.Electric field drift is generated by introducing into electric field in CFQS magnetic field configuration,and the particle orbit equation has been modified.The poloidal drift enhance and the particle loss rate in the loss channel decreases along increasing of electric field.It indicates that poloidal drift improves ability of particle confinement in CFQS magnetic field configuration.By increasing the magnetic field component,the magnetic field heterogeneity is significantly enhanced,particle loss rate is reduced and special loss channel influence is decreased.However,the magnetic field toroidal inhomogeneity is enhanced,which means the phenomenon of local axisymmetry-breaking is more obvious.Therefore,further investigate and analysis of increasing magnetic field components.By changing the component zero,it is found that the radial drift weakens and the particle loss rate in the loss channel decreases.The maximum J region and the toroidal reversal particle precession occur when component zeros move with increasing magnetic flux.It improves ability of particle confinement in CFQS magnetic field configuration,so as to improve the plasma constraint.