A critical assessment of thermal-hydraulic modeling of HTS Twisted-Stacked-Tape-Cable conductors for fusion applications

Reliable analyses of thermal-hydraulic (TH) transients are becoming fundamental to support the design of magnets for fusion applications based on High Temperature Superconducting (HTS) Cable-In-Conduit-Conductors (CICCs). However, currently available TH codes were developed and validated only for the analysis of magnets wound with Low Temperature Superconductors (LTS) CICCs. In order to confirm the applicability of such tools also to HTS CICCs, a two-step strategy is presented in this paper. First, a qualitative assessment of the characteristic time and spatial scales in HTS CICCs, based on the Twisted-Stacked-Tape Cable (TSTC) concept, has been performed. It shows that the different geometry and materials of TSTC strands lead to heat transfer time scales on the conductor cross section, which are comparable to those of fast transients, ranging from milliseconds to few seconds, e.g. quench initiation and propagation as well as AC losses. Therefore, the assumptions of temperature uniformity on the cross section, typical of the well-established 1D codes developed for LTS magnets, become questionable. A second, quantitative assessment, based on detailed electro-thermal models of the conductor and of the single TSTC strand cross-section, provides guidelines for the development of more reliable 1D models for the analysis of TH transients in HTS fusion magnets.