SupraFusion is a French exploratory program dedicated to the development of high-temperature superconductors (HTS) to address future energy and societal challenges, using fusion applications as a driving motivation for this research. In particular, the program aims to design, manufacture, and test a large-scale HTS demonstrator magnet. To achieve this objective, a stepwise development strategy has been adopted, relying on smaller mock-ups and prototypes to qualify the key technological building blocks of the final demonstrator.One of the main risks in the development of the demonstrator is ensuring safe operation in the event of a quench. Due to their low normal zone propagation velocities, quenches in HTS magnets are difficult to detect and may lead to severe coil damage caused by the Joule heating deposited in the conductor. To address this challenge, the first prototype developed within the SupraFusion program, referred to as D0, is designed to investigate quench propagation and detection in a copper-stabilized insulated HTS coil and qualify numerical models to be ultimately used for designing the large-scale demonstration magnet.The D0 prototype conductor will first be wound as a single-layer spiral on a stainless-steel mandrel with a bending radius of 60 mm. The mandrel will then be assembled with large feeders soldered to the conductor to ensure a reliable electrical connection. To ensure a homogeneous thermal distribution, the entire device will be actively cooled using forced-flow supercritical helium. The D0 prototype coil will finally be inserted into the OPTIMIST background field solenoid, providing a magnetic field of 9 T. The design objective is to operate the prototype up to 20 kA and 4.5 K, under a magnetic field close to 10 T. Under these operating conditions, the prototype will enable the investigation of several key aspects of the technology, including quench propagation velocity, conductor hot-spot temperature, quench protection system sensitivity, the use of HTS Superconducting Quench Detectors (SQD), and the conductor critical current.At present, the main design aspects of the D0 prototype have been completed. These include magnetic field and load-line margin calculations, thermoelectric studies of the electrical connections, cooling strategy and thermal distribution analysis, mechanical behavior under electromagnetic loads, and the integration of the prototype into the MATTRICS cold test facility. In parallel, the first preparatory D0 samples representative of the final D0 prototype were manufactured and tested in liquid nitrogen. These samples made it possible to validate the winding process of the conductor on its mandrel without degrading its critical current, to characterize the electrical contact resistance between the conductor and the feeders, and to install heaters and voltage taps. They also enabled preliminary investigations of quench detection using a Superconducting Quench Detector based on REBCO tape.These initial results allowed improvements to the sample fabrication process and enabled the project to progress toward the final stages of the study: fabrication of the final D0 prototype conductor, installation in the MATTRICS test station, and the upcoming measurement campaigns.
