Evaluation of the nonlinear surface resistance of REBCO coated conductors for their use in the FCC-hh beam screen

Abstract

To assess the feasibility of using high-temperature superconductors for the beam screens of future circular colliders, we have undertaken a study of the power dependence of the microwave surface resistance in state-of-the-art REBCO coated conductors at about 8GHz and 50K. We have employed a dielectric resonator to produce radio-frequency electromagnetic fields on the surface of the coated conductors having amplitudes similar to those generated by proton bunches circulating in the vacuum chamber of the proposed hadron-hadron Future Circular Collider at CERN. We show that surface resistances in REBCO coated conductors without artificial pinning centers are more affected by a radio-frequency magnetic field than those containing nano-inclusions. Despite that, at 8GHz, 50K, and 9T, most REBCO coated conductors studied outperform copper in terms of surface resistance, with the best sample having a 2.3mO surface resistance while being subject to an RF field 2.5 times stronger than that in the FCC-hh. We also extrapolate the measured data to 16T and 1GHz, the actual FCC-hh dipole magnetic field, and mid beam frequency spectrum, demonstrating the possibility of lowering the surface resistance of the vacuum chamber by up to two orders of magnitude compared to copper. Further, we discuss the correlation between the time structure of the electromagnetic fields provided by vector network analyzers compared to the proton bunches' time structure in the collider and present the effect of low alternating magnetic fields on vortex displacement and the possibility of demagnetization of superconducting samples.

The authors acknowledge the support and samples provided by Bruker HTS GmbH, Fujikura Ltd, SuNAM CO Ltd SuperOx, SuperPower Inc. and Theva Dünnschichttechnik GmbH. This work was supported by CERN under Grant Nos. FCC-GOV-CC-0072/KE3358, FCC-GOV-CC-0153/KE4106 and FCC-GOV-CC-0208/KE4947/ATS. UPC funding was also provided through the Unit of Excellence María de Maeztu MDM2016-0600. N Tagdulang and A Romanov acknowledge MSCA-COFUND-2016-754397 for the PhD Grant. ICMAB authors acknowledge RTI2018-095853-B-C21 SuMaTe from MICINN and co-financing by the European Regional Development Fund; 2017-SGR 1519 from Generalitat de Catalunya and COST Action NANOCO-HYBRI (CA16218) from EU, the Center of Excellence award Severo Ochoa CEX2019- 000917-S.

Peer Reviewed

Postprint (published version)