Global analysis of radio-frequency current drive

Abstract

A theoretical analysis of radio-frequency current drive in a tokamak at frequencies much less than the electron cyclotron frequency is presented. The global model includes kinetic hot plasma effects and collisions. All kinds of wave-plasma interactions (resonant wave-electron interaction, resonant wave-ion interaction and collisions) can contribute to the current drive. The analysis discusses the following current drive components: the momentum-transfer current and polarization current, the helicity current, the resonant and non-resonant currents, the currents caused by kinetic and collisional effects. The two most important new current drive components are introduced, the resonant helicity current and the collisionless part of the non-resonant current. Helicity current drive is proportional to the parallel helicity flux. The helicity conversion coefficient, expressing the conversion of the parallel helicity flux into the parallel induced current, is defined by the wave-plasma interaction. The collisionless part of the non-resonant current is proportional to wave damping on ions. However, this is an electron current, and wave-ion interaction just creates necessary polarization of the wave to drive a current. Circularly polarized waves drive a current differently from linearly polarized waves, and wave polarization is an important factor for current drive efficiency.