POWER ABSORPTION DURING NONLINEAR ELECTRON CYCLOTRON WAVE-PARTICLE INTERACTION

摘要

A numerical model for ECRH and ECCD which consistently takes into account nonlinear wave-particle interaction has been developed. The results of computations show that the distortion of the particle distribution function from Maxwellian is strong for parameters typical for present day ECRH experiments. This leads to a reduction of the absorption, consequent broadening of the absorption profile and incomplete absorption. It should be mentioned that the distortion of the particle distribution function is essentially different from what is expected from the quasilinear theory where a Fokker-Planck equation is assumed to be valid. The positive derivative of the distribution function indicates that nonlinear effects of ECRH may cause the electron Bernstein wave instability. The modelling of ECCD at the 2nd harmonic X-mode resonance shows that the effect of power redistribution in velocity space can especially be important for current drive. Therefore, for ECCD the absorption should be taken into account correctly by using nonlinear computations. It should be mentioned that the noise in the right picture in Fig. 7 due to poor statistics in the tail of the distribution function where the main part of the current is generated can be resolved using the weight-windows algorithm, that will be realized in future computations. With increasing both magnetic field and size of the beam, the nonlinear effects become more important (ε_(NL) is increasing). Therefore, the proper account of nonlinear effects is ultimate for reactor-scale devices.