In hole-doped cuprates there is now compelling evidence that inside the pseudogap phase, charge order breaks translational symmetry. In YBa 2 Cu 3 O y charge order emerges in two steps: a 2D order found at zero field and at high temperature inside the pseudogap phase, and a 3D order that is superimposed below the superconducting transition T c when superconductivity is weakened by a magnetic field. Several issues still need to be addressed such as the effect of disorder, the relationship between those charge orders and their respective impact on the Fermi surface. Here, we report high magnetic field sound velocity measurements of the 3D charge order in underdoped YBa 2 Cu 3 O y in a large doping range. We found that the 3D charge order exists over the same doping range as its 2D counterpart, indicating an intimate connection between the two distinct orders. Moreover, our data suggest that 3D charge order has only a limited impact on low-lying electronic states of YBa 2 Cu 3 O y .

The aim of the NOUGAT project is to design and realize a 10 T high temperature superconducting solenoidal insert able to operate in a 20 T background magnetic induction. Our design is based on the metal-as-insulation winding technique consisting of co-winding a bare REBCO high temperature superconducting tape with a stainless steel tape. The metal-asinsulation winding maintains the self-protection feature of the no insulation winding and helps to reduce current charging time constants-one of the major drawbacks of no insulation coils-by significantly increasing the turn-to-turn electrical resistance. First, we demonstrated the selfquench protective behavior at 4.2 K under a high field up to 17 T by testing a single-pancake prototype. Then, before fabricating the final insert, we designed, wound and tested a second prototype made of two double-pancakes. The purposes were three-fold: validating the winding and assembly process, confirming the operating margins and corroborating the mechanical study. In this article, we present the main results of the tests performed at 4.2 K on this sub-scale prototype in a high background magnetic field at

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