Assembly and Test Results of the RMM1a,b Magnet, a CERN Technology Demonstrator Towards Nb₃Sn Ultimate Performance

As part of the High Field Magnet technology development carried out at CERN, demonstrators are under construction to explore the full potential of Nb ₃ Sn. The Racetrack Model Magnet (RMM) is one of them, building upon the successful Enhanced Racetrack Model Coil (eRMC) eRMC1a magnet which reached 16.5 T peak field or 16.3 T bore field at 1.9 K. The RMM1a,b magnet is composed of the same two previously tested eRMC racetrack-type coils and an additional middle RMM coil. This central racetrack-type coil features a closed cavity with a diameter of 50 mm and a total length of 526 mm. The coil pack is assembled in the same shell-based support structure as eRMC1a, using bladders and keys to allow for a precise control of the preload with minimal spring back and conductor overstress. The magnet was preloaded with a conservative approach limiting the equivalent peak stress in the coil blocks below 150 MPa. It was then successfully tested up to 16.7 T peak field or 16.5 T bore field at 1.9 K. This paper describes the assembly of the RMM1a,b magnet, relying on Finite Element Analysis (FEA) and mechanical instrumentation, as well as the powering test results at 4.2 K and 1.9 K.