As part of the High-Field Magnet (HFM) technology development program at CERN, significant steps have been recently made in the Racetrack Model Magnet (RMM) program. RMM is a demonstrator[1] with a 50 mm open bore and a coil based on flat racetracks, launched in 2016 in EuroCirCol studies[2]. It features all the complexity of a dipole for accelerator, except the presence of flared ends. In 2022, the first powering of the demonstrator reached the record bore field of 16.4 T[3],[4] .
RMM1 powering tests (J. C. Perez, G. Willering, S. Izquierdo Bermudez, et al.)
After a second assembly aiming at improving the mechanical aspects, the RMM1 magnet has been tested in November 2024; it exceeded the previous bore field of 0.5 T, giving 16.95 T at 1.9 K; the magnet reached 16.0 T at 4.5 K. At this field level the peak prestress induced in the coil is order of 170 MPa. The demonstrator had flattop quenches above 16 T, but it was able to hold for several hours the maximum field of 15.75 T. Data were presented at the HFM forum[5]. This proves that Nb3Sn technology has an adequate margin to operate at 14 T, as set in the FCC-hh baseline design. The next step is to reassemble RMM to improve aspects related to cooling, and then assembly a second magnet RMM2 in 2024 with a new set of coil, to verify the reproducibility of the manufacturing performance.
[1] By demonstrator (different definitions can be found in the literature) we mean a magnet having not all features of the final design but aiming to prove some aspect of the technology.
[2] S. Izquierdo Bermudez, et al. "Design of ERMC and RMM, the base of the Nb3Sn 16 T magnet development at CERN” IEEE Trans. Appl. Supercond. 27 (2017) 4002004
[3] J .C. Perez, et al. "Construction and Test of the Enhanced Racetrack Model Coil, First CERN R&D Magnet for the FCC” IEEE Trans. Appl. Supercond. 32 (2022) 4005105
[4] E. Gautheron, et al. "Assembly and Test Results of the RMM1a,b Magnet, a CERN Technology Demonstrator Towards Nb3Sn Ultimate Performance” IEEE Trans. Appl. Supercond. 33 (2023) 4004108
[5] G. Willering, et al. “Test of RRM1d” HFM forum Nov 7 2024 https://indico.cern.ch/event/1464833/