Superconductors for Tokamak poloidal field coils

The a.c. losses and stability of a number of model conductors for Tokamak poloidal field coils were evaluated. The conductors employ mixed matrix NbTi superconductor cabled with copper stabilizer and were tested with insulated strands, bare strands and solder filled. Data are presented for total loss per cycle as a function of maximum field and of field sweep rate. These losses are separated into filament hysteresis loss, filament coupling loss, stabilizing strand eddy loss and interstrand coupling loss. The data are compared with the predictions of a new theory which models the conductor as a LR circuit closely coupled to the magnet. Data are also presented for the velocity of propagation of recovery of a normal zone, the full recovery current and the minimum propagating current. The dependence of stability on the degree of coupling between the strands and on the amount of helium present in the cable is also discussed.