Reduction of toroidal ripple by using high Tc conductors

The loss of alpha particles in a rippled toroidal field is one of the most critical issues for the design of tokamak reactors, because it has direct impacts on the design of toroidal field (TF) coils and the first wall. In the preliminary design of the ITER, the alpha particle ripple loss and the additional first wall heat load due to such loss has been assessed. From these assessments the maximum ripples (Bmax - Bmin)/(Bmax + Bmin), at the plasma edge is required to be decreased to 1 - 1.5%. There are several possible ways to decrease the ripple value without changing the TF coil shape. One of them is to use ferromagnetic balls in the vacuum vessel under the outer TF coil legs. Preliminary estimations show that in this way the ripple can be decreased by a factor of 2. In this paper, a new method to reduce the toroidal ripple using high Tc superconductors is presented. High Tc superconductor have the advantage of working above the boiling temperature of liquid nitrogen and they have other properties that make their practical applications. For example, they behave as a ferromagnetic or diamagnetic material depending on their magnetization. Therefore, if superconductors are appropriately arranged and magnetized, they decrease the maximum ripple at the plasma edge to the required value