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 helium has been developed at KfK. It allows position independent installation and well controlled operation which would be advantageous for operation of all kind of superconducting forced-flow cooled magnets. The design of the lead is described in this paper. The main feature is the insertion of Nb₃Sn wires inside the conductor of the heat exchanger allowing the operation at minimum mass flow in a wide current range. Measurement results are presented for steady-state operation up to 30 kA, for short time operation up to 50 kA, for pulsed operation up to ±1000 A at 10 Hz, and for simulation of loss of mass flow. A high-voltage 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 effectiveness of the Nb₃Sn inserts. Comparison to numerical calculations shows good agreement allowing extrapolation for the design of leads for currents up to 80 kA for ITER model coil tests in the TOSKA test facility at KfK