Beam Impedance Mitigation in the CERN Future Circular Collider

Abstract: CERN has recently started a Design Study for a possible next-generation high-energy hadron-hadron collider (Future Circular Collider – FCC-hh). The FCC-hh calls for an unprecedented center-of-mass collision energy of 100 TeV, colliding proton beams of 50 TeV steered in a 100-km circumference tunnel by 16 T superconducting magnets. The beams emit synchrotron radiation at high power which, to optimize cryogenic efficiency, is absorbed by a beam-facing copper-coated screen held at 50 K. The surface impedance of this screen has a strong impact on the beam, and copper at 50 K does not allow sufficiently beam stability margins.
This motivates investigating High-Temperature Superconductors (HTS) coatings, as a possible solution. In this frame calculations of the surface resistance of HTS in high field, low frequency regimes are presented and discussed, in order to identify materials parameters that would allow a reasonable advantage in respect to copper.