Stability evaluation of a conduction-cooled prototype LTS pulse coil for UPS-SMES

The stability of a prototype conduction-cooled LTS pulse coil for UPS-SMES of 100 kJ was evaluated. This coil has been developed as a first step of a project to develop a 1 MW, 1 UPS-SMES to protect semiconductor chip production equipment and nuclear fusion experimental devices, etc, from momentary voltage drop and power failure. The winding conductor is an NbTi/Cu Rutherford cable, which is extruded with aluminum. This conductor has both low AC losses and high stability under specified orientation of changing transverse magnetic fields. The 100 kJ-coil are wound by the new winding method. In order to improve the heat conduction properties in the coil, Dyneema FRP and Litz wires are used as spacers. Litz wires were connected with the cryocooler as cooling paths. On the pulse operation, the operating current is reduced from 1000 A to 707 A in 1 s. In this paper, the thermal properties of the 100 kJ-coil are calculated by finite element method under pulse operation. In order to estimate the stability, a calibration experiment was carried out. Results indicated that our prototype LTS pulse coil has high stability to enable to allow over 10 times as large heat as AC losses.