Experimental qualification of the first DTT TF superconducting cables in SULTAN

The objective of this work is the experimental qualification of the performance of the first ENEA superconducting (SC) cables for the toroidal-field (TF) coils of the Divertor Tokamak Test (DTT) Facility that is being built in Frascati [1]. Two full-scale, short-length conductor samples with different twist-pitch have been tested from the begin of July 2022 in SULTAN, a test facility operated by EPFL-SPC (Swiss Plasma Center) and located at Paul Scherrer Institute (PSI) in Villigen, Switzerland. In this one-of-a-kind magnetic facility, the superconductors have been tested in a forced flow of supercritical Helium with nominal current and magnetic field up to 11 T. Before testing, the SC cables made of Nb3Sn were prepared in the facility: they underwent heat-treatment and were assembled and instrumented with high precision thermometers, voltage taps and, in the case of one of the two samples (the TF-B one), also equipped with pressure capillaries to allow a more precise hydraulic characterization. In the three-week test campaign, hydraulic tests and power tests (both DC and AC) with current and field were carried out to assess the performance of the SC samples. The main performance parameters for a SC magnet were investigated in specific tests: experiments on critical current and current sharing temperature (DC tests), minimum quench energy MQE tests and AC loss measurements. Applying cyclic electromagnetic loads to the sample, the performance degradation after cycles was investigated, measuring periodically the current sharing temperature and analyzing the broadness of the transition to the normal conducting state. Also, the degradation after two thermal cycles (warm-up and cool-down) were assessed. The measurements of current sharing temperature at different EM loading conditions (i.e., different current and applied field) were also carried out, allowing the analysis of the cable strain under different Lorentz forces. The important results emerged from the detailed analysis of the tests of the first two TF samples (hydraulic characterization, DC and AC tests) are reported in this thesis.