REBCO HTS (Rare-earth barium copper oxide high-temperature superconducting) tapes, have a high potential for winding of large magnet coils [1-2]. TORT (Tapes on Round Tube) cables represent a promising option for achieving a conductor suitable for the winding of magnet coils. However, certain applications, such as accelerator magnets, require the use of superconducting cables with low magnetization AC losses. There are several methods to reduce AC losses in TORT cables. Our first approach was to get rid of eddy currents by replacing the copper former with dielectric materials based on polymers and composites, i.e. PETG CF (polyethylene terephthalate glycol-modified reinforced with carbon fibres) or PC CF (polycarbonate with carbon fibres) [3]. Additional reduction of hysteretic loss was achieved by striating of HTS tapes [4-5]. Moreover, hot spot formation in the HTS tapes can significantly degrade the superconductor, especially in the case of striated tapes. We compared the performance of several concepts of thermal stabilisation layers, focusing on their high thermal capacity and thermal conductivity, low electrical conductivity, coefficient of thermal expansion matching with the tape, and mechanical and chemical stabilisation function. We investigated several material concepts (based on e.g. AlN—Cu, Al2O3—Cu) in form of multilayers. Subsequently, striated tapes with thermal stabilisation layers were then wound onto electically non-conductive formers, and then the short TORT cable was electromagnetically characterized at different frequencies. The design and experimental analysis of the stabilisation layers of modified tapes, as well as the whole TORT cable, were supported by FE (finite element) analysis.
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This work was supported by: (1) the Slovak Research and Development Agency, project No. APVV-20-0056, (2) the Grant Agency of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences, project No. 1/0205/21, (3) by European Regional Development Fund, project No. ITMS2014+: 313011BUH7.