Effects of Toroidal Field Ripples on the Bootstrap Current in Tokamaks

Abstract

The effects of toroidal field ripples on bootstrap current in the low collisionality regime in tokamak plasmas are discussed by using an asymptotic expression of the bootstrap current. When the toroidal field ripple is 1-3%, an 8-15% reduction of the bootstrap current is predicted in a tokamak plasma having q = 1.8 and ε_t = 0.3. If we fix the ripple ratio, dependence on the number of toroidal field coils is negligible when the number is more than 15. These results suggest that the effect of the toroidal field ripple on the bootstrap current is particularly important when the pressure gradient is steep near the plasma edge.