Superconducting magnetic systems are the ultimate enabling technology for fusion device, based on magnetic confinement concept. The most advanced fusion reactors exploit superconducting magnets based on low temperature superconductors that may be cooled at liquid helium temperature. However, in perspective of sustainable commercial fusion reactors, the possibility to use high temperature superconductors (with operation temperatures > 4.2 K) offer clear technological advances with higher efficiency in cooling and reduction in the reactor complexity. High temperature YBa₂Cu₃O_7-d (YBCO) coated conductors offer a realistic vision for high field (B > 13 – 20 T), low temperature (T < 50K) conditions of fusion devices. In general pinning performance of YBCO films have been optimized for applications in liquid nitrogen temperature (65-77K) at intermediate fields (0-5T) and up to date, relatively poorly knowledge exists on their performance at low temperatures.

The fabrication of nanostructured REBCO thin films, by the incorporation of nanosized oxide secondary phases, has been shown to strongly enhance their pinning performances ensuing great potential for technological expectances. For that, pinning landscape needs to be adjusted and optimized at a specific Temperature-Field range, required for each application. In this contribution we will present high-performing YBa₂Cu₃O_7–x layers fabricated by chemical solution deposition methodology (CSD) through novel barium-deficient low-fluorine solutions which are distinguished for being straightforward, inexpensive, and eco-friendly. We will discuss on the pinning performance of pristine and nanostructured YBCO layers grown by CSD where processing conditions were tuned to obtain the best defect landscape for future fusion magnets. Transport critical current density measurements performed up to 9 T, between 5-90K allowed us to draw a general H-T diagram with different characteristic fields to compare and discuss on the pinning performances achieved for CSD and PLD nanocomposites, at different operating conditions.

Keywords: YBCO, pinning, nanocomposite, CSD