High temperature superconductor coated conductors for the FCC-hh collider beam screen coating

2019 edition

Artur Romanov

In 4 July 2012, CERN announced the experimental confirmation of the Higgs boson. It resolves the mystery of how particles receive their mass, completes the Standard Model of particle science and resulted in the award of the 2013 Nobel Prize for Physics. This achievement marks a milestone in physics history and is a glaring justification for the financial investments and decades of brought in man-power required for realizing a particle accelerator facility. In attempt to continue the progress beyond the lifetime of the LHC, an initiative for the R&D of a 100 TeV proton-proton collider of 80-100 km circumference, the so-called Future Circular Collider (FCC), was kicked off. Particle collisions with such high energies give prospect to unravel tantalizing riddles related to dark matter and supersymmetry.

Part of the FCC study is to rethink the design of the beam screen. This particle accelerator component is necessary in order to thermally shield the cold bores of the steering magnets from the synchrotron radiation that is naturally emitted by charged particles held on a circular trajectory.

The design concept of the LHC beam screen is based on an octagonal shaped stainless steel tube coated in its interior with copper. In the foreseen operating conditions of the FCC, i.e. 40-60 K, 16 T and 0-1 GHz proton bunch frequency, the intended Cu coating might not guarantee a surface impedance sufficiently low for a stable beam.

The only known materials that might have a lower surface resistance at given conditions are superconductors. Since January 2017, the Superconducting materials group at the material science institute in Barcelona (ICMAB-CSIC), which I am part of, started a collaboration with CERN to evaluate the suitability and optimization of REBa2Cu3O7-x (RE = Y, Gd) high temperature superconductor (HTS) coated conductors, a structure consisting of a superconducting material layer on top of a flexible, metallic substrate, as a coating for the FCC beam screen. Besides the exceptional high surface conductance, HTS tapes require also an unperturbed superconducting performance under synchrotron irradiation and a low secondary electron yield which is defined as the number of emitted electrons upon one impinging electron.

In this contribution, the general scope of the FCC study is introduced and a special focus will be dedicated to the challenges and possibilities of using HTS tapes as a beam screen coating both of which are object of my PhD thesis.