Physical Research On Helicon Wave Current Driving And Antenna On CFETR

Fusion reactors need to maintain and regulate the distribution of current profiles through off-axis current driving.The high order harmonic fast wave,also called the helicon/spiral wave,which can propagate into central region without high density limitation,in addition,the current drive is comparable to lower hybrid current drive(LHCD).Therefore,it has a highly potential off-axis current driving method for the future fusion reactor.The helicon wave off-axis current driving is one of the key issues in the China Fusion Engineering Experimental Reactor(CFETR).Based on the main parameters of the CFETR,in this dissertation,the investigations of the helicon wave off-axis current drive(HWCD)simulations and helicon wave antenna design have been carried out.The dissertation also states the principle of propagation and absorption of helicon waves and the accessibility of helicon wave.The physical models of numerical calculation of HWCD are introduced,including the basic principles and methods of ray propagation trajectory and current drive calculation.Using the numerical simulation codes,consideration of the CFETR operation parameters and the equilibrium files,the simulations for HWCD has been carried out.The influence of the frequency,the antenna parallel refractive index,the poloidal emission position of the ray and the plasma parameters(electron temperature and electron density)on the driving current distribution and driving efficiency are analyzed.The main results are shown as follow:1)The effective off-axis current drive can be achieved by launching the ray from the equatorial plane with the wave source frequency greater than 1GHz;2)The rays from the 45° poloidal angle(The poloidal angle is defined as follows:the middle plane in the low field sideis 0° and the middle plane in the high field side is 180°,counterclockwise rotation of 360° can contain the entire poloidal profile),or near the middle plane of the high side,the drive efficiency is higher;3)The parallel refractive index of the antenna is within the range of 2-3.4,which has little effect on the profile of the driving current and driving current efficiency;4)With the increase of the central electron density,the current peak value of the drive decreases,driving efficiency decreases;5)With the increase of the center electron temperature,the peak value of the driving current increases,but the current profile becomes narrower and shifts to the outside of the plasma.Finally,the dissertation involves the physical design of the helicon wave antenna.Based on the basic theory of the traveling wave antenna,the physical model of CFETR helicon wave traveling wave antenna is established by using the three-dimensional electromagnetic simulation software--CST.The characteristics such as scattering parameters,near-fields and surface current are analyzed.The structural parameters of the HW antenna are optimized,including the strap length,width,interval between straps and the number of straps.In order to evaluate the coupling performance of the helicon wave antenna,simulations of the CFETR antenna reference model with dielectric media and cold plasma loaded has been performed by using the finite element analysis software COMSOL.The basic coupling characteristics of reference antenna such as near-fields and the coupling impedance are provided.The simulation results will provide a theoretical guidance for the CFETR current driving antenna mechanical design.