subSMCC1 is a 4-layer stress-managed common coil (SMCC) magnet, which constitutes an important milestone towards a 14-T demonstrator magnet for FCC-hh. subSMCC1 was built to validate the concept of stress-managed common-coils, to test a variety of novel technologies and processes for the winding former insulation, winding, reaction, impregnation, instrumentation splices, and impregnation, as well as a novel clam-shell structure.

The magnet was designed and manufactured at PSI. It was successfully tested at CERN, reaching 98% of its theoretical maximum performance at 4.5 K, and 95% of maximum at 1.9 K. Additionally, the magnet demonstrated good memory after the thermal cycle. All quenches in this test campaign occurred above 90% of maximum performance.

With this result, the team at PSI is well-prepared for the upcoming conceptual design review of the first full high-field stress-managed common coil to be built over the next calendar year.

We would like to acknowledge the support of the CHART initiative and the HFM program, hosted at CERN, for funding this project. Our sincere thanks also go to the Lawrence Berkeley National Laboratory for providing the Nb3Sn cable, and to CERN for their contribution to the protection studies and the reaction of 2 out of the 4 coils, which was successfully carried out at CERN.