Effect of toroidal field ripple on particle and energy transport in a tokamak

The azimuthal asymmetry introduced in tokamaks by the use of a finite number of toroidal field coils can lead to anomalously large particle and energy losses. The diffusion and ion heat transport coefficients associated with the ripple-induced drift of particles trapped in the usual banana orbits have been calculated and the results compared with the coefficients for neoclassical banana transport in axisymmetric tokamaks, transport governed by the dissipative trapped-ion instability, and the transport associated with particles trapped between the coil planes by the ripple field itself. The calculations were performed for an Experimental Power Reactor design and show that the losses due to the ripple-induced banana drifts can be a major limit on fusion reactor magnet design. (author)