Operational experience with the combined solenoid/dipole magnet system of the COMPASS Experiment at CERN

The first ever polarized Drell-Yan measurements were performed at the COMPASS experiment at CERN in 2015, making use of a transversely polarized ammonia target using Dynamic Nuclear Polarization (DNP). A 2.5T longitudinal field is generated with a superconducting solenoid coil carrying a nominal current of 650A, while high homogeneity is obtained by using additional shim - and compensation coils. A superconducting dipole coil encloses the solenoid and together they are integrated in a common cryostat. To obtain transverse polarization, the target material is first polarized in the stronger longitudinal solenoid field and after that, it is rotated to the less strong transverse dipole field (0.63T at 590A). The absolute field strength is never allowed to drop below 0.48T to guarantee a high polarization percentage. In the meantime the forces between the coils should be limited and therefore, the coils cannot both be carrying the nominal operational current, since this will destroy the system. The magnetic field rotation procedure is therefore uniquely developed for this system. The total system is slightly over 2m in length and the stored energy of the system is 2.58MJ for the solenoid at 650A and 0.468MJ for the dipole at 590A.