Quench Simulation of Superconducting Magnets: with Commercial Multi-Physics Software

The simulation of quenches in superconducting magnets is a multiphysics problem of highest complexity. Operated at 1.9 K above absolute zero, the material properties of superconductors and superfluid helium vary by several orders of magnitude over a range of only 10 K. The heat transfer from metal to helium goes through different transfer and boiling regimes as a function of temperature, heat flux, and transferred energy. Electrical, magnetic, thermal, and fluid dynamic effects are intimately coupled, yet live on vastly different time and spatial scales. While the physical models may be the same in all cases, it is an open debate whether the user should opt for commercial multiphysics software like ANSYS or COMSOL, write customized models based on general purpose network solvers like SPICE, or implement the physics models and numerical solvers entirely in custom software like the QP3, THEA, and ROXIE codes currently in use at the European Organisation for Nuclear Research (CERN). Each approach has its strengths and limitations, some related to performance, others to usability and maintainability, and others again to the flexibility of material parameterizations. In this context the master thesis mainly involves the study of the strengths and limitations of the first approach. The primary goal of the thesis is to build a 1D numerical model representing a superconducting wire based on existing physical models. An adiabatic model has been constructed, to solve one of the five boundary value problems involved in the quench, both in ANSYS and in COMSOL. The temperature dependent material properties and loads are defined using function tools in COMSOL and by creating look up tables in ANSYS. The models were validated with QP3 and compared in terms of performance, stability and accuracy. The helium-cooled model is built only in ANSYS. The model solves two of the five boundary value problems simultaneously as a coupled problem. Apart from generic numerical code (transient thermal analysis), a separate algorithm is needed to define the non-linear heat transfer between the metal and the helium. For this ANSYS Parametric Design Language (APDL) scripts are used. During the analysis the ANSYS transient thermal codes are executed several times within a loop. There are three different types of helium cooled models. All models were validated with QP3. The results obtained from comparisons show that the adiabatic models were able to simulate quenches with the desired accuracy. The adiabatic analysis in the commercial simulation tools is more efficient and stable for various scale of spatial discretization. Similarly, the helium-cooled models are able to simulate quenches with satisfactory accuracy. Nevertheless, the models are not compatible with automatic time stepping method of the simulation environment. The use of fixed time stepping method in the models resulted the coupled analysis in ANSYS to be far more time consuming than in QP3.