On the 19th of June 2020, the European Strategy Group announced the 2020 update of the European Strategy for Particle Physics, identifying the ambition to operate a proton-proton collider (FCC-hh) at the highest achievable energy as long term future priority. CERN’s FCC-hh is the most ambitious scenario for a post LHC machine. It will operate as an 80-100 km acceleration ring where 16-18 T magnets will steer proton bunches producing center-of-mass collision energies of 100 TeV. In order to protect the superconducting magnets, the 35.4 W/m/beam synchrotron radiation emitted by the protons will be absorbed by a stainless steel tube, the so called beam-screen chamber, held at a temperature window of 40-60 K. Image currents will be induced into the steel walls of the beam-screen endangering the beam stability. To counteract this effect, the interior of a beam-screen chamber has to be coated with a highly conductive material. Our consortium explores the possibility to replace the conventional beam-screen coating Cu with REBa₂Cu₃O_7-x (RE = rare earth) Coated Conductors (CCs) in order to increase the beam stability margin.

In this contribution, we demonstrate why commercially available REBCO CCs are promising candidates for the FCC-hh beam screen coating. Critical current densities measured up to 9 T at 50 K, which is the operating reference temperature of the beam screen chamber, point towards a superconducting performance that can sustain the induced peak image currents of 25 A at FCC conditions. We present the surface resistance R_s of CCs and Cu colaminated on stainless steel at 8 GHz and in a wide range of cryogenic temperatures and magnetic fields. We find that CCs outperform Cu under operating conditions close to those to be found in the FCC-hh. In addition, high frequency vortex parameters like the depinning frequency are extracted from the data by fits with the Gittleman-Rosenblum model. This allows a discussion on the limits of the mean-field model and the correlation between surface resistance and microstructure of different REBCO CCs. The next steps towards an aspect ratio study of Cu and CCs in order to minimize trapped fields in the beam screen chamber, their assembly in the beam screen and the expansion of measurement conditions to the more realistic 16 T and 1 GHz will be discussed.