TEST OF A FORCED-FLOW COOLED 30-KA 23-KV CURRENT LEAD FOR THE POLO MODEL COIL

A 30 kA / 23 kV current lead cooled by forced-flow supercritical heliu m has been developed at KfK. It allows position independant installati on and well controlled operation which would be advantageous for opera tion of all kind of superconducting forced-flow cooled magnets. The de sign of the lead is described in this paper. The main feature is the i nsertion of Nb3Sn wires inside the conductor of the heat exchanger all owing the operation at minimum mass flow in a wide current range. Meas urement results are presented for steady-state operation up to 30 kA, for short time operation up to 50 kA, for pulsed operation up to +/- 1 000 A at 10 Hz, and for simulation of loss of mass flow. A high-voltag e test up to 28 kV DC has been done. The mass flow rate normalized to current is about 0.055 g/(s-kA) for 15 to 30 kA proving the effectiven ess of the Nb3Sn inserts. Comparison to numerical calculations shows g ood agreement allowing extrapolation for the design of leads for curre nts up to 80 kA for ITER model coil tests in the TOSKA test facility a t KfK.