DEVELOPMENT AND TEST OF THE POLOIDAL FIELD PROTOTYPE COIL POLO AT THEFORSCHUNGSZENTRUM-KARLSRUHE

A superconducting prototype (3 m empty set and nominal current 15 kA) of a poloidal field coil was developed, constructed and tested accordi ng to the typical specification of the Tokamak magnet system in collab oration with European industry. In order to withstand fast ramping(sim ilar to 2 T s(-1)), plasma disruption (80 T s(-1), 10 ms) and plasma c ontrol (similar to +/- 0.05 T, 10 Hz) in the superconducting state a l ow loss conductor and a well developed high voltage technique at 4 K w ere indispensable attributes of the design. The sc cable of the conduc tor consists of mixed matrix strands (NbTi in Cu/CuNi) cooled by a dua l cooling system (two phase forced flow helium for heat removal at con stant temperature, and stagnant helium for good transient stability). The sc cable is inclosed in a thick walled stainless steel jacket. All coil components are designed and constructed according to the rules o f the high voltage technique. The coil was tested in the TOSKA facilit y at FZK-Karlsruhe. For generating the typical positive and negative m agnetic field transients a special high power switching circuit of a d ischarge power up to 700 MW (30 kA, 23 kV) was constructed and used. T he coil was investigated considering its superconducting, electromagne tic and mechanical properties. All results were conclusive in agreemen t with calculations and fulfil the specifications. A highlight is that for this conductor type the stability against transient field changes is only determined by the expected stability margin or the critical c urrent boundary no other limitations of the ramp rate were observed. ( C) 1997 Elsevier Science S.A.