Theoretical Analysis Of The Interaction Between ICRH Antenna System And Plasma

Ion cyclotron resonance heating(ICRH) has been validated as a main candidate for auxiliary heating for present-day tokamaks and future international thermonuclear experimental reactor(ITER) in the world.It not only can effectively heat the plasma ions or electrons, but also can control sawtooth and improve plasma confinement. Investigation on the interaction between ICRH antenna system and plasma is of great significance for the steady-state and high-performance operation of the future nuclear fusion reactors.The antenna input impedance changes due to varying plasma conditions of ICRH, and it is small compared with the characteristic impedance of the transmission line under the limitation of voltage breakdown for certain current. These two characteristics of antenna load make how to futher improve plasma coupling energy and the antenna system’s impedance matching important for the research on controlled nuclear fusion theory. In this paper, the ICRH antenna and plasma coupling is firstly studied through the three-dimensional(3-D) antenna, planar, cold-plasma and single pass model. The Maxwell equations in the vacuum and the fast magnetosonic wave equations in the plasma are solved respectively by Green’s function method and a variable step length fourth-order Runge-Kutta method. The effect of two poloidal symmetrically aligned ICRH antenna straps’ phase difference on the asymmetry of the coupling characteristics, the influence of two toroidal symmetrically placed ICRH antenna strips’ distance on plasma coupling charecteristics, and the relationships of four toroidal and poloidal symmetrically arranged ICRH antenna straps’ current distribution, feeder’slength and density distribution with plasma coupling charecteristicsare simulated and discussed emphatically. Then, according to transmission line theory and the antenna input impedance obtained by the coupling calculation, the paper analyzes the the triple liquid stub tuner’s impedance matching for ICRH and the resonant double loop(RDL) antenna’s impedance matching for edge localized modes(ELMs) plasmas.The main simulation results show that : 1) the asymmetry of radiated energy in poloidal direction can be controlled through changing the phase difference of two poloidal symmetrically aligned ICRH antenna straps. If the phase shift meets, the increase of the phase lag corresponds to the increase of asymmetric degree in poloidal coupling. However, the opposite phenomena will appear if the phase shift meets. When the phase lag equals to, the asymmetry in poloidal coupling tends to become most obvious. 2) When two toroidal symmetrically placed antenna strips feed in phase, the spectral components of zk which deviate from zero(corresponding to the best absorption) decrease with the antenna distance increase, and the antenna radiated power utilization is low, the total energy absorbed by plasma from wave reduces. So the shorter the antenna distance is, the better ion cyclotron resonance heating is. 3) If the other experimental parameters are same, the antenna radiated power to the vacuum increases as the feeder length increases, the antenna radiated power for the symmetric current is more than the antisymmetric current. The density in the SOL leads to the increase of coupling energy, which may be due to the reduction of wave attenuation length from antenna to cutoff layer. 4) When the density profile changes, the matching liquid heights for the triple liquid stub tuner vary more smoothly than that of the case when the wave frequency varies on conditon that the other experimental parameters are same. At certain frequencies, the tuner may need more complex steps to get matching, which may ruduce its adjust speed. 5) If the other experimental parameters are same, the best feeder location of the RDL antenna is gradually far from the central point of it when the frequency becomes lower or coupling resistance becomes larger. 6) For the wave frequency of 40 to 70 MHz, a reasonable layout of the optimum RDL feed location is demonstrated to be useful for tunable capacitors’ insensitivity to the changes of the antenna input impedance during ELM discharge, which may reduce the engineering and technical requirements of adjustable capacitors. The related simulation results provide certain reference for the optimal design of ICRH antenna system and setting of experimental parameters.