  In fast wave current drive, the resonant electron is accelerated by fast wave
in the direction parallel to the static magnetic field, and the parallel
velocity will be increased. The trajectories of the trapped resonant electrons
are calculated with a computer code in which fast wave-induced diffusion in
velocity space is accounted for by a quasi-linear operator. The simulation
results show that the orbit of trapped resonant electron will change from a
trapped orbit to a passing orbit in some cases. We obtain the transition
conditions, and if they are satisfied the trapped orbit will become a passing
orbit. The transition from trapped orbit to passing orbit implies that the
effect of trapped electrons on current drive will be reduced and the current
drive efficiency will be improved.
