Calibration of a superconducting transformer by measuring critical current of a NbTi Rutherford cable

Abstract: Large high field superconducting magnets often requires high current superconducting cables. In order to develop these cables, a facility capable of providing high magnetic field with large sampling area as well as electrical current of tens of kA is essential. A superconducting transformer is an energy-efficient and low-cost way to provide large current to superconducting cables. Previously, we co-developed a superconducting transformer and successfully tested it to a maximum output current of 45 kA in zero magnetic field. In this work, this superconducting transformer is installed to the 12 T split solenoid magnet at the National High Magnetic Field Laboratory (NHMFL). We calibrated it by using this facility to measure critical current of a NbTi Rutherford cable as a function of magnetic field up to 10 T, and compare the results with those available in the literature. In addition, a strand extracted from the NbTi cable is tested for critical current. The critical current of the extracted strand is scaled and compared with critical current of the cable. The accuracy of the critical current measurement using this superconducting transformer is discussed in detail. This work concludes the commissioning of this superconducting transformer which combined with the 12 T split magnet will provide unique cable testing capability for future cable development for the NHMFL and its users.