HTS Coatings for Impedance Reduction in Particle Accelerators: Case Study for the FCC at CERN

The FCC-hh presently under study at the European Organization for Nuclear Research (CERN) will make use of 16-T superconducting dipoles for achieving 100 TeV p-p center-of-mass collision energy in a 100-km ring collider (see https://edms.cern.ch/document/1342402/1.0). A beam screen will shield the 1.7 K dipole cold bores from the 28 W/m/beam of synchrotron radiation, operating at 50 K as the best compromise temperature in order to minimize the wall-plug power consumption of the cryogenic system. In the Large Hadron Collider (LHC), presently operating at CERN, a stainless steel beam screen optimized for operation at 20 K is coated with an 80-mu m copper layer in order to minimize beam coupling impedance. However, copper operating at 50 K might not provide low enough beam coupling impedance in the FCC-hh. It has then been proposed in the private communication by L. Rossi to minimize it by adding a thin layer of a high-temperature superconductor. The purpose of this paper is to describe the basic properties of a superconductor in the RF field induced by beam image currents and exposed to a high magnetic field, to study the validity of the approach, and to identify the best candidate materials and coating processes.