Effects Of Resonant Magnetic Perturbation On The Loss Of Energetic Particles

From the late of 1950 s to now,the magnetic confinement nuclear fusion has gained great progress,but there are still some unsolved problems,such as the confinement of energetic particles(energetic ions and runaway electrons).In tokamak plasmas,energetic ions include the alpha particles generated from the nuclear fusion reaction and fast ions generated by the auxiliary heating,such as neutral beam injection(NBI).The energetic ions are extremely important for the heating and momentum input of the plasma and their loss is harmful to the stable operation and the lifetime of the tokamak.Moreover,if the seed runaway electrons are generated and are not expelled from the plasma in time,they will form runa way current by avalanche amplification.And if the runaway current hits the wall of the tokamak in the form of energetic electron beam,it will seriously harm or even break down the wall of the tokamak.On the other hand,the resonant magnetic perturbation(RMP)is extensively applied to suppress or mitigate the edge localized mode(ELM)in tokamak pedestal,but can break the tokamak magnetic field configuration,which will deteriorate the confinement of energetic ions and make them lose from the plasma.Therefore,it is of great importance to investigate the effects of RMP on the loss of energetic ions.The tokamak can confine the charged particles very well due to its axisymmetric magnetic field configuration.But when the axisymmetry of the magnetic field is broken,the bounce/transit average of the radial drift velocity for energetic ions is nonzero and the drift loss of energetic ions may occur.At present,the effects of RMP on the loss of energetic ions are mainly attributed to orbit resonance.When the ratio between the toroidal precessional frequency and bounce frequency of energetic ions satisfies a certain condition,the orbits of energetic ions can resonate with the RMP and then escape from the plasma.But for energetic ions in pedestal,the strong radial electric field can influence the toroidal precessional frequency and then affect the drift loss of energetic ions.In addition,the RMP can also break the tokamak magnetic field and form stochastic magnetic field,which will increase the level of stochastic transport of energetic ions.The foci of this thesis are the drift loss of energetic ions induced by the perturbed non-axisymmetric magnetic field in tokamak pedestal and the transport loss of energetic ions induced by the stochastic magnetic fluctuation.For the drift loss of energetic ions in pedestal,using the single particle orbit model and neglecting the effects of finite Larmor radius and the width of the banana/transit orbit,this thesis derives the equations of motion of energetic ions,including the bounce/transit averaged radial drift and toroidal precession modified by the strong radial electric field.Taking typical plasma parameters in the pedestal of DIII-D,this thesis calculates the drift loss time of energetic ions numerically and analyzes the parametric dependences of the drift loss time.The main conclusions include:(1)passing energetic ions can be well confined and will not escape from the plasma;(2)deeply trapped energetic ions can lose from the plasma,but the loss range of parameters is narrow;(3)the drift loss time of trapped energetic ions decreases with the increase of the energy of energetic ions,the maximum amplitude of the RMP,the safety factor at the axis and the peaking factor of the plasma current density profile,and increases with the increase of the absolute value of the minimum radial electric field,the pitch angle-like parameter and the poloidal mode number of the RMP.This means that the RMP makes the confinement of energetic ions generated by perpendicular NBI weaker than that of energetic ions generated by tangential NBI.The strong radial electric field in pedestal significantly reduces the toroidal precessional frequency of trapped energetic ions,which plays an important role in the loss of trapped energetic ions.Furthermore,we find that the drift loss time is smaller than the slowdown time by three orders of magnitude.Therefore,the drift loss of trapped energetic ions induced by the RMP is an important loss mechanism for the DIII-D pedestal.For transport loss induced by stochastic magnetic fluctuations,this thesis improves the radial stochastic diffusion coefficients for different limiting cases and obtains the general connection formula for the radial stochastic diffusion coefficient for arbitrary spectrum width.Our general formula can reproduce the results obtained by J.R.Myra both analytically and numerically.Moreover,this thesis calculates the radial stochastic diffusion coefficients of alpha particles and runaway electrons in ITER and that of runaway electrons in J-TEXT.we find that the stochastic magnetic fluctuation induced transport loss of alpha particles and neutral beam injection generated energetic ions is not significant.However,the transport loss of runaway electrons induced by the stochastic magnetic fluctuation is very important,especially for the future large tokamak.Therefore,increasing the transport loss of seed runaway electrons by enhancement of the stochastic magnetic fluctuation,the formation of runaway current could be avoided in the future large tokamak.