The Study Of Fast Ion Loss Due To Toroidal Field Ripple On EAST

The confinement and transport of fast ion is a very crucial issue in the magnetic fusion machine and not only affect the efficiency of auxiliary heating but the fusion yield. The origin of fast ion consist of neutral beam injection, radiofrequency heating and fusion reaction, so in the real tokamak machine always contain electrons, ions of different energy, species and charge states, and also some neutral particles. These fast ions experience drift orbits that are much larger than the thermal particles in the background plasma. A goal of fast ion loss study is to understand the effect of the background plasma and its electromagnetic field on the fast ion behavior.Due to the discrete and corrugated nature of the magnetic field coils, the toroidal field of tokamak will have a non-axisymmetric component. The possible excursions of fast ion from the magnetic flux surface may introduce anomalously particle and energy loss through stochastic ripple loss and ripple trapped loss process. The main content of the paper’s work is the analysis of experiment result in the 2014 EAST campaign experiment. Among the different and complicated auxiliary heating methods on EAST, the highly successful method on raising plasma temperature in the EAST experiment is neutral beam injection, so the following paper work will focus on the study of the beam ion ripple loss. After doing analysis of the experimental results, we obtained the dependence of the fast ion ripple loss on the plasma current and on the pitch angle of fast ion distribution. In the same time, we have carried out an experiment for the study of fast ion behavior from the decay of neutron emission following a short neutral beam injection. In addition, in order to investigate the transport and confinement of fusion alpha particles in future reactors, such as Chinese Fusion Engineering Test Reactor, the paper has calculated preliminarily the alpha particle ripple loss from the present design parameters.The calculation is carried out with a Hamiltonian guiding center drift orbit Monte Carlo code ORBIT, plasma shape equilibrium reconstruction and fitting code EFIT and tokamak experiment transport analysis code TRANSP. The paper’s content is organized and will be introduce as follows:in the first chapter, the basic tokamak structure, auxiliary heating and current drive system are introduced; the origins and loss mechanisms of fast ions are overviewed and explained. In the chapter two, we have summarized two distinct ripple loss processes in the complicated magnetic ripple field, such as ripple trapped loss and stochastic ripple diffusion. These are dominant loss mechanism for fast ions in plasma without MHD activities. We also analytically constructed the Hamiltonian formulation of the guiding center motion of charged particle in the toroidal magnetic field which not possesses good magnetic flux surfaces. In the chapter three, based on the EAST physical experiment campaign of 2014, the paper have calculated the fraction of beam ion ripple loss with different plasma current and ion pitch angle, it is interesting to note that the fast ion ripple loss fraction is a monotonic decrease with plasma current, which means the ripple and prompt loss are strongly dependent on the profile of safety factor. At the different time, the left ion source and the right ion source is inject fast particle in the 48583 shot, so the distribution of fast ion pitch angle can be used to study the ripple loss dependence on the ion pitch angle. The purpose of NBI blip experiment is to study the transport and loss of fast ion from the time evolution of neutron emission. The decay rate of 2.5 MeV D-D fusion neutrons mainly produced by beam-plasma reactions on EAST was measured. The experimental decay data was compared with neutron decay model predicted by classical mono-energetic slowing down approximation. The results show that the slowing down time of fast ions during the NBI blip experiment on EAST agree well with classical theory, and they followed classical slowing down model and no significant loss in an MHD-quiescent plasma. The results also indicated the fast ion introduced by NBI has a peaked profile and the neutron is mainly produced by the beam-target reaction in the core plasma. In the chapter four, we calculated the fusion produced alpha particle ripple on Chinese Fusion Engineering Test Reactor with orbit following Monte Carlo code, which was run with plasma equilibrium flux surfaces generated by the equilibrium code EFIT and different alpha model source profile. The particle loss prediction for the steady phases of the pre-sawtooth peaked profile is that 0.1 to 0.4% of the normal shear configuration. Calculation of reversed magnetic shear case predicted that the alpha particle ripple loss is near 5.6%. The ripple loss fraction is very localized and predicted to increase several times with flat source profile or sawtooth-broadened profile, which bring challenge for steady state operation of fusion reactor. The last chapter summarized the main content of this paper and do some prospect for the further investigation of fast ion loss.