SCIENTIFIC HIGHLIGHTS RL2, Articles

Superconductors substituting copper for the future circular collider beam screen (FCC-hh) at CERN

The FCC-hh considers a novel utilization of coated conductors reliant on the high frequency response of high-temperature superconductors under extremely challenging working conditions

The FCC-hh is the most ambitious scenario for a post Large Hadron Collider (LHC) machine proposed by CERN. It will operate as a 80-100 km acceleration ring where 16-18 T magnets will steer 1011 protons in 8 cm bunches with revolution period of 0.3 ms. In this machine, collision energies of 100 TeV are expected to be reached. 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, held at a temperature window of 40-60 K. The beam screen chamber is located in the beam-steering superconducting magnetic dipoles to thermally shield them. Given the prospected beam parameters, mirror charges will be induced into the beam screen that peak at magnitudes of 25 A and wiggle with frequency spectrum 0-1 GHz. Governed by the necessity to maintain a stable beam during acceleration of hadrons, highly conductive coatings will have to cover the interior of the beam screen chamber.

Scientists from the Superconducting Materials and Large Scale Nanostructures (SUMAN) at ICMAB have proposed a solution to this challenge: coating the beam screen chamber with a high-temperature superconductor (HTS) instead of copper. Compared to copper, which is already used in CERN’s LHC, HTS promise with their lower surface resistance and thus, bigger beam stability margins at operation temperature. HTS of the type REBa2Cu3O7-x (where RE is a rare earth metal, such as Y, Gd or Eu), are produced worldwide as flexible materials in hundreds of km length and could be ideal candidates. In this work, scientists within a consortium made by SUMAN-ICMAB, ALBA, IFAE and UPC have demonstrated that REBa2Cu3O7-x HTS are capable of outperforming copper’s surface resistance by a factor of 40 or more under the extreme working conditions to be found in the FCC-hh.

Coated Conductor technology for the beamscreen chamber of future high energy circular colliders
Teresa Puig, Patrick Krkotic, Artur Romanov, Joan O'Callaghan, Danilo Andrea Zanin, Holger Neupert, Pedro Costa Pinto, Pierre Demolon, Ângelo Rafael Granadeiro Costa, Mauro Taborelli, Francis Perez, Montse Pont, Joffre Gutierrez, Sergio Calatroni
Superconductor Science and Technology 32, 094006 (8pp), 2019
DOI: 10.1088/1361-6668/ab2e66

Figure: Left pannel: Experimental values of the surface resistance of coated conductors are lower than that of copper at working conditions close to those found in the FCC-hh. Right pannel: The theoretical predicions based on our experimental values show that coated conductors have a 40 times lower surface resistance at the FCC-hh working conditions (16T and 1 GHz) as compared to copper. Insert to right pannel: Sketch of the cross section of the FCC-hh beam screen chamber coated with stripes of REBa2Cu3O7-x coated conductos (black regions).

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