Heat Transfer in High Field Superconducting Accelerator Magnets

Abstract

This monograph comprehensively describes the problem of heat transfer in superconducting accelerator magnets, which generate high magnetic fields and are cooled with superfluid helium at temperature of 1.9 K or normal fluid helium at a temperature of 4.2 K. The main objective of the research presented in the monography was to optimize the heat transfer in superconducting magnets in terms of their operation in accelerators. The magnets are affected by the shower of secondary particles generated by the particles lost from the beam or particle debris from experiments. The optimization of heat transfer in the superconducting magnets is essential for accelerator efficiency during the collection of the data for physics analyses. The quench of magnets stops accelerator operation and affects the integrated luminosity The superconductors 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 particles lost from the beams or coming from the collision debris are hitting the vacuum pipe and generating a shower of secondary particles, which deposits energy in the magnets coils causing increase of the conductor temperature above a critical one and in consequence provokes the quench of magnets. A quench is the transition of a conductor from the superconducting to the normal conducting state which occurs irreversibly in the superconducting magnets if one of the three parameters: the magnetic field, the current density or the temperature exceeds a critical value. In the research described in this monography the studied critical parameter is the temperature and the figure of merit is the energy deposited in the conductor volume at which the quench occurs. This monograph contains the historical background and the overview of existing methods of solving of the heat transfer problem in multilayer systems, for example in the superconducting magnets. An essential part of the monography is the presentation of the original approach to the problem of optimizing the heat flow in superconducting magnets, designed and developed by the author of this monography and the experimental validation of this method carried out in the form of mini-experiments, planned and executed by the author at CERN. In the monograph the details of calculations and measurements for the superconducting magnets currently installed and operating in the LHC are described as well as the status and analysis of superconducting magnets developed for the LHC upgrade in ~2025. The monograph focuses on the heat transfer from the superconductor to the heat exchanger through a multilayer structure made of solid elements and channels occupied by the normal fluid or the superfluid helium. This monography summarizes many years of the author’s work and experience in this field and includes: the description of the model, the summary of the results obtained for the superconducting magnets installed in the LHC, the results of mini-experiments carried out at CERN and FERMILAB and a description of applications of the developed model in the process of design of a new superconducting magnets for the LHC upgrade. The examples of alternative numeric calculations and measurements are briefly discussed and extended bibliography is presented.