Reduction of the cyclic stress fatigue due to the over-turning force on the toroidal field coils by quasi-steady operation in a tokamak fusion reactor

It is shown that the cyclic stress fatigue due to the over-turning force on the toroidal field coils in a tokamak fusion reactor can be greatly reduced by appropriately changing the plasma current in the recharging phase of the quasi-steady operation scenario with the use of lower hybrid wave current drive. This substantial reduction is made possible, if the characteristics of required variation of the equilbrium magnetic field for the dee-shaped divertor plasma is properly taken into account in adjusting the plasma current, in which the necessary equilibrium field becomes larger in low beta phase than in high beta phase for the same plasma current.