Ripple Loss of Alpha Particles in a Low-Aspect Ratio Tokamak Reactor

Studies on the loss of fusion produced alpha particles enhanced by toroidal field (TF) ripple in a low-aspect-ratio tokamak reactor (VECTOR) have been made by using an orbit-following Monte-Carlo code. In actual TF coil systems, the ripple loss of alpha particles is strongly reduced as the aspect ratio becomes low (the power loss is proportional to A8.8 for A>˜2.5) and the reduction of the number of TF coils results in a large amount of ripple losses even in a low-aspect-ratio tokamak. Judging from the allowable peak heat load on the first wall (≈1MW/m2) due to loss particles, the number of TF coils of VECTOR can be reduced fro 12 to 10 without changing the coil size, and in addition, the number can be reduced to 8 with ferrite plates. To reduce the number of TF coils from 12 to 6, about 40% of coil size enlargement is necessary. By using ferrite plates, the coil size enlargement for N=6 can be reduced to about 15%.