CERN’s Future Circular Collider (FCC) is the most ambitious scenario for a next generation particle accelerator. With 16T magnetic fields in a 100 km acceleration ring, center-of-mass collision energies of 100 TeV will be reached. To shield the steering superconducting magnets from the 35.4 W/m/beam synchrotron radiation emitted by the particle beam, a highly conductive metallic structure, the beam screen, surrounds the particle trajectory, absorbing the radiation, at a temperature window of 40 – 60 K. During operation, image currents will be induced in the beam screen, risking beam stability. To minimize this destabilizing effect, our consortium studies a hybrid coating for the beam screen, made of CU and REBaCuO (RE = rare earth) Coated Conductors (CCs). This combination ensures not only a low surface impedance, but also meets the field homogeneity criterion of a few units over 10000 imposed by CERN, which is necessary to preserve proper particle trajectory. In this work, we use the finite elements method and H-formulation to explore the field quality of the hybrid coating when submitted to the dipole and quadrupole fields that will be applied to the beam screen. Since the angle of the magnetic field with regards to the superconductor will be different along its width, particularly for the quadrupole field, our model accounts for the anisotropy of the superconductor, as well as creep effects and the field dependence of the superconducting properties. We analyze how field harmonics are affected by displacing and tilting the beam screen with regards to the external field and how they change over time during beam injection. Finally, we discuss the possibility of using the hybrid coating with the correction circuits of the dipole magnets to achieve a combined effect to partially cancel some of the field harmonics, increasing field homogeneity.

Keywords: Future Circular Collider, REBCO, Field Quality, Beam Screen Coating