Experimental and Numerical Investigation on Losses in Electrodynamic Transients in a Nb3Sn Prototype Racetrack Coil

The detailed knowledge of the current and losses distribution during the electrodynamic transients is of great importance for the design of superconducting accelerator magnets made of Rutherford cable. On the one hand, the current distribution affects the field harmonics generated by the superconducting magnet; on the other hand, losses strongly affect the design of the cryogenic system and may jeopardise the magnet stability. The THELMA code has been used to model an experimental ac test carried out on one sample of the so-called short model coil, developed and tested at CERN in the frame of a test campaign of possible cable candidates for the HL-LHC CERN project. In this test, the coil was fed with a transport current cycle at constant temperature. The coil losses were determined with an electrical approach, starting from the measured coil voltage and current. THELMA can represent the Rutherford cable at the strand level, making it possible to analyze the interstrand current diffusion and the corresponding losses in detail. From this analysis, a qualitative agreement between measured and computed losses, together with useful hints for further and more accurate models have been obtained.