Object-oriented modelling for LTS and HTS superconducting cables

Superconducting (SC) cables and magnets in the past decades have enabled fundamental discoveries in the field of high-energy physic, amazing steps forward in the research on a clean energy based on nuclear fusion and a significant increase in the power transfer capability, as well as reduction of transmission loss and construction cost, for power cables. Different kinds of SC cables are available, according to the applications, based on different SC materials and different concept for their cooling (conduction-cooling, coolant bath of forced-flow). The SC cables for fusion, for instance, are mainly based on a thousand of thin strands, embedding the low-critical-temperature superconducting (LTS) material, twisted together and pulled inside a metal jacket (the so-called cable-in-conduit concept). The coolant, supercritical Helium at 4.5 K and 5 bar flows inside the porous matrix originated by the strands. The SC cables for power transmission typically adopt high-critical-temperature superconducting (HTS) tapes, stacked on a stabilizing former and cooled by a forced flow of liquid nitrogen at 77 K. The cables are surrounded by the cryostat. Focusing on forced-flow SC cables, which are crucial both for fusion applications and for power transmission, the availability of an appropriate, reliable and flexible modelling of the SC cables is of paramount importance. In the field of fusion cables, several numerical tools are well established for the analysis of the transients in fusion (LTS) cables, as the 4C code, developed at DENERG few years ago. In the field of power transmission cables, few numerical tools are available for the HTS cables, based on a very simplified modelling. A single model, flexible enough to cope with both LTS and HTS cables for fusion applications and power transmission, respectively, is missing from the research arena. The aim of the present thesis is the conceptual development of a single tool for the analysis of thermal-hydraulic transients in SC cables, though from the very beginning to be capable to model LTS, as well as HTS cables. Euler-like sets of 1D equations should be used to model the fluid flow along the cable, for an arbitrary number of fluid regions in single phase. The fluid equations need to be coupled to 1D transient heat conduction equations, for the SC strands/tapes and for the stabilizer elements and jacket/insulation layers/cryostat. The spatial grid used to discretize the equations with a finite element scheme should account for non-uniform elements distribution along the cable, while the time-marching scheme should take advantage of an adaptive time stepping. The model should be developed based on a user-friendly concept of a graphical interface that allows to easily define the cable topology, to choose the appropriate numerical solvers and run the simulations, checking the evolution of selected thermal-hydraulic variables during the code execution. In perspective, the model needs to be extended to include also a lumped electrical model.