The effect non-linear wave-particle interaction on ECRH with helical ripple stellarators
Abstract
Particles trapped in the helical ripples in stellarators bounce back and forth along the magnetic field line. Trapped particles get energy from the wave repeatedly. When the turning points are far from the resonance region, the heating process is stochastic and the wave-particle interaction makes a small perturbation on the distribution function. The rate of velocity-diffusion for the leading order distribution function is proportional to the sum of squares of the wave amplitudes. This is the, so called, "quasi-linear diffusion theory" since linear absorption and quadratic diffusion are used. However, quasi-linear theory is not valid when the turning points are very close to the resonance region and the particles stay in the resonance region such as in second harmonic X mode ECRH. When this is the case, the wave and particles are correlated and the stochastic process is not viable. To obtain ECRH heating in this nonlinear regime, collisions need to be explicitly accounted for. Nonlinear wave-particle interaction for deeply trapped particles has been described in previous work. In this work, the equivalent diffusion term when nonlinear wave-particle interaction dominates will be derived. It is desired to look for steady-state solution of the Fokker-Planck equation when the heating term and the Coulomb collision term are balanced in order to analyze power deposition.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..DPPRP1030S