Flow Generation Associated with RF Current Drive in a Tokamak Plasma

Full text: Radial electric field can be built by the charge accumulation due to resonant trapped electron pinch, when the rf wave is injected, and then drive the toroidal flow. The resonant pinch effect is evaluated for the parallel-drive scheme. It is found the radial electron flux and its driven electric field is proportional to the rf power density and also proportional to the rf driven current density. However, the efficiency of the radial electron flux drive decays exponentially with respect to the square of the parallel phase velocity of the wave. For LHW, the parallel phase velocity is a few times of the electron thermal speed, therefore the momentum deposited on trapped electron is rare otherwise the upshift of the N|| spectrum is obvious. To generate typical radial electric field with order of 10 kV/m, it is needed ∼ 10 kW/m3 power density deposited on the thermal electrons, which is a few percentage of 1 MW/m3 for current drive. When low frequency wave, e.g. fast wave or Alfven wave is applied, the current drive efficiency is weaken due to enhanced collisional dragging and electron trapping, but there is high efficiency for the electric field generation and flow drive. (author)