The Implementation of Thermal-Electrical Analogy to Quench Limit Determination of Superconducting Magnets

D. Bocian (Inst. of Nuclear Physics PAS, Poland)

The superconducting magnets are an essential part of large particle accelerators. The superconductors used in coils of these magnets are characterized by the critical surface determined by three parameters: the critical temperature (Tc), the critical current density (Jc) and the critical magnetic field (Bc). The energy deposited in the superconductors by the particles lost from the accelerated beams or coming from the experiment collision debris may heat up the conductor in the magnet coil and provoke the quench, namely an irreversible transition of the superconductor from the superconducting to a normal conducting state. That is why the main challenge of the accelerators operating with the superconducting magnets is their protection against the energy deposits to the coils from the particles lost from the beam and determination of the energy limits at which beam should be dump from the accelerators in order to avoid the magnets quench. The thermo-electrical analogy was used to develop a model of the magnets which has been used to study the thermodynamic behavior of magnet coils and to determine the quench limits of the LHC magnets for expected beam loss profiles. The developed Network Model was used also for thermal analysis of Nb-Ti magnets and for optimization of Nb3Sn quadrupole magnets developed for use in the LHC luminosity upgrade. The analysis focuses on the heat transfer from the superconductor to the heat exchanger through a multilayer structure of magnet made of solid elements and channels occupied by the normal fluid or the superfluid helium. This paper shows the details of quench limit calculations and validation measurements of the superconducting magnets currently installed and operating in the LHC as well as the status and analysis of superconducting magnets developed for the LHC upgrade in ~2025.