Progress on REBCO Based Conductors for Nuclear Fusion Applications

In recent years, the impressive performance improvement and commercial production capability increase of Rare-Earth Barium-Copper Oxides (REBCO) High-Temperature Superconductor (HTS) tapes is triggering a great interest in the perspective of applications for extremely high magnetic field generation as in nuclear fusion and high-energy physics sectors. In particular, for nuclear fusion, since the ‘50s proposed as one of the most exciting energy sources due to its nominally unlimited, efficient, and eco-sustainable characters, HTS based technologies can play a revolutionary role. The concrete perspective of high-performing HTS conductors operating in a wide temperature range and extremely high fields, inaccessible by other traditional Nb-based superconductors, is promoting new concepts of plasma-magnetic confined fusion devices to emerge. It is generally recognized that the commercial exploitation of fusion energy will only be feasible if the magnetic system will use a technology based on HTS materials. Hence, the development of a suitable HTS magnet technology is a key step towards the successful achievement of these goals.<br/>In this presentation, the current status of the HTS conductor development for fusion applications will be firstly reviewed and discussed taking into account the conductors developed for both large (DEMO-like) and compact (SPARC) tokamak machines and other concepts of fusion devices [1, 2]. Then, a high current REBCO Cable-In-Conduit (CIC) conductor, conceived for large fusion magnet applications based on aluminum slotted-core incorporating a number of HTS tape stacks, will be presented in detail. The conductor layout, designed aiming at the industrial feasibility of the manufacturing process, has shown promising electrical, thermo-hydraulic, and mechanical properties assessed in several experimental studies of cable samples. More recently, the thermal stability of such a cable has been addressed in dedicated experiments for the investigations of quench phenomena. The designing and the manufacturing of CIC conductor samples (targeting more than 15 kA at 11 T at 4.2 K), aimed at the investigations of thermal stability and quench behavior under fusion relevant conditions to be performed at the SULTAN facility (Swiss Plasma Center), will be presented. The development of a new HTS CIC conductor targeting 60 kA at 18 T at 4.2 K will be also described and the first experimental test campaigns will be presented. The perspectives of this CIC conductor for DEMO central solenoid insert coil applications as well as for DTT (Divertor Tokamak Test facility) [3] applications will be at the end drawn and discussed.<br/>References<br/>[1] K. Sedlak, et al., <i>Advance in the conceptual design of the European DEMO magnet system</i>, Supercond. Sci. Technol. 33 (2020) 044013 (9pp).<br/>[2] Z. S Hartwig, et al., <i>VIPER: an industrially scalable high-current high temperature superconductor cable</i>, Supercond. Sci. Technol. 33 (2020) 11LT01 (8pp).<br/>[3] L. Giannini, et al., <i>Conceptual Design studies of an HTS insert for the DTT Central Solenoid</i>, presented at EUCAS 2021 (virtual conference September 5^th – 9^th).