Banana drift diffusion in a tokamak magnetic field with ripples

The drift motions of trapped particles in a tokamak field with ripples lead to a new transport process in large tokamaks in addition to the diffusion process due to particles trapped in the ripples. This problem is studied by solving the bounce-averaged drift kinetic equation with a model collision operator. It is shown that the “banana drift diffusion” is proportional to the collision frequency when the poloidal banana drift frequency is smaller than the effective collision frequency. This result is contrary to earlier predictions. In a reactor regime, this loss mechanism is shown to be unimportant.