Experimental Validation of Superconducting Model Circuits for High-Luminosity Project at CERN: Flux Jumps and Magnet Transfer Functions

The Nb$_{3}$Sn superconducting MQXF quadrupole and the 11-T dipole magnets represent a new technology enabler for future high-energy particle accelerators: the former aims at reducing the beam size by a factor two and increasing the rate of collisions by a factor of five; the latter, instead, will be able to provide the same integrated field as the standard 8.3 T LHC dipole, but in a shorter length, thus freeing up space for additional collimators for reducing the beam losses produced by the higher intensity beams of the HL-LHC. A possible impediment comes from flux jumps that, so far, could not be avoided by design. They are usually detected as voltage jumps between different magnet coils but they might also produce overall voltage jumps across the magnet electrical terminals. The first part of this work aims at: (i) presenting preliminary experimental test results on the previously introduced Nb3Sn model and prototype magnets and (ii) attempting to build a simplified electrical model of the flux jumps. Magnetic fields are used to control particle beams in accelerators and are usually controlled by regulating the electrical current of the power converters. However, what is directly acting upon the beam is the magnetic field and not the current of the power converter, which undergoes several frequency-dependent transformations until the desired magnetic field, seen by the beam, is obtained. Based on B field measurement results on the $short$ model of HL-LHC MQXF magnets, the second part of this work aims at: (i) presenting simple admittance measurements in frequency domain and (ii) attempting to reconstruct the frequency response from power converter voltage to B-field seen by the beam.