Speaker
Description
The SPARC compact, high-field tokamak developed by Commonwealth Fusion Systems and the Massachusetts Institute of Technology is based on high temperature superconductor (HTS) magnets. This device employs 8 Poloidal Field PF magnets which are made with PIT-VIPER cable wound in pancakes, the smallest measuring 1.2 meters radius, and the largest 8 meters. There are 10-14 pancakes in each magnet, each of these pancakes with their own grading scheme. The performance of each of these pancakes must be verified in liquid nitrogen before integration into SPARC. To this end we present the development of the qualification process for the PF magnets, covering the design of the test stands as well as the evolution of the thermo-electromagetic models. The test stands are able to deliver up to 24 kA while ensuring appropriate support for the self-field, Lorentz forces, but without sacrificing the testing pace required by the SPARC schedule. The models take into consideration the twisted topography of the cable, the pancake’s geometry, grading schemes as well as the HTS allocated to create a prediction of the critical current Ic at 77K, self-field. But measuring this is not an easy feat. Because the grading scheme is designed for the SPARC’s 20K-20T performance, an additional thermodynamic model is necessary to design the current ramps to safely test the pancakes in liquid nitrogen.
