Conceptual Design Improvement of a Toroidal Field Coil for EU DEMO Using High-Temperature Superconductors

In the frame of the preconceptual design of the next-generation fusion power plant (EU DEMO), the PROCESS systems code is used for nearly 20 years, in which the main reactor components (e.g., plasma, blanket, and magnets) are integrated in a unique computational algorithm and simulated by means of rather simplified mathematical models (e.g., steady-state and zero-dimensional models). In this paper, the boundaries given by the PROCESS code for the toroidal field coil (TFC) of EU DEMO are used as a starting point for the design of a TFC winding pack, using the high-temperature superconductor (HTS) material REBCO as alternative to Nb3Sn. As the DEMO system code parameters are under continuous adjustment, the PROCESS outcome of the July 2012 version is used. This defines the cable space area, the winding pack current density, and the total current in one TFC to generate the required magnetic field on the plasma axis. Based on this and as an extension of the work, the electromagnetic, structural mechanics, cooling, and thermohydraulic properties of an HTS-TFC are presented, and parameters such as operation current, magnetic field and Lorentz forces, operation temperature, structural requirements, cooling, and quench performance are calculated. It is shown that HTS material can be used for the TFC of EU DEMO. At present, the design is made at an operation temperature T op = 4.5 K, allowing adaptation to higher temperatures if the material properties shall improve in the future.