Electron Cyclotron Wave And High Harmonic Fast Wave Current Drive In Tokamak Plasmas

In order to obtain the steady-state operation of tokamak plasma with high performance, the plasma current should be driven and controlled non-inductively. Electron cyclotron waves(ECW) and high harmonic fast wave current drive are two important ways for non-inductive current drive. Thus, those studies are of significance in controlled nuclear fusion. In this thesis, with the quasi-linear theory, the electron cyclotron wave current drive(ECCD), high harmonic fast wave(HHFW) current drive, the current drive with combined the two waves, and the suppression of magnetohydrodynamic(MHD) instabilities with ECW will be investigated theoretically and numerically. The main results are listed as follows:1. A new ray-tracing and Fokker-Planck code has been developed with the radio frequency wave current drive theory. The code is benchmarked with other well-tested codes and is then used to study the ECCD on the HL-2A tokamak. The wave propagation, power deposition and driven-current profiles are presented. It is found that quasi-linear effects are negligible at the present ECW power levels, and the current drive(CD) efficiency saturates at ～0.029×1020A/W/m2 and ～0.020 X 1020 A/W/m2 for the 0.5MW/68GHz first harmonic ordinary(O1) and 1MW/140GHz second harmonic extraordinary (X2) modes, respectively. The effects of the plasma density, temperature, and wave-launching position on the driven current are also presented.2. Current driven with HHFW in EAST tokamak plasmas is studied. The HHFW CD efficiency is found to increase non-monotonically with the wave frequency, and this phenomenon is attributed to the multi-pass absorption of HHFW. The study also shows that the CD efficiency increases first then decreases with the increasing of the parallel refraction index. The quasi-linear effects, assessed as significant in HHFW current drive with the GENRAY/CQL3D package for the first time, cause a significant increase in CD efficiency as RF power is increase. The presence of the DC field can also increase the CD efficiency.3. The current driven by combined ECW and HHFW is investigated with the GENRAY/CQL3D package. It is shown that no significant synergetic current is found in a range of cases with combined ECW and low frequency F W. However, with the enhancement of the F W frequency, positive synergy effect does appear in tokamak for the first time. This positive synergy effect can be vividly explained with the picture of the electron distribution function induced by ECW and the very high harmonic fast wave (helicon). The dependence of the synergy effect on the wave power is also analyzed.4. The capabilities of current drive, neoclassical tearing mode (NTM) stabilization and sawtooth control are analyzed for the electron cyclotron wave system on.HL-2M tokamak. The effect of launching angle and position on current drive has been obtained and the wave power needed to stabilize NTM have been given. For both NTM stabilization and sawtooth control, good performance of the upper launcher is demonstrated in comparison with that of a dropped upper launcher. In addition, for the performance of the three mirrors in equatorial port, the middle mirror launcher has high current drive capabilities and more localized current density profile, thus is more suitable for NTM stabilization and sawtooth control.In conclusion, this thesis addresses several basic questions on ECCD, HHFW current drive, the current drive with combined the two waves, and the suppression of MHD instabilities with ECW. The theoretical and numerical results presented here will contribute to the understanding of the physics of non-inductive current drive, and the achievement of the high performance steady-state operation for tokamak plasmas.