Coated conductor technology for the beamscreen chamber of future high energy circular colliders

The surface resistance of state-of-the-art REBa2Cu3O7-x coated conductors has been measured at 8 GHz versus temperature and magnetic field. We show that the surface resistance of REBa2Cu3O7-x strongly depends on the microstructure of the material. We have compared our results to those determined by the rigid fluxon model. The model gives a very good qualitative description of our data, opening the door to unravel the effect of material microstructure and vortex interactions on the surface resistance of high temperature superconductors. Moreover, it provides a powerful tool to design the best coated conductor architecture that minimizes the in-field surface resistance. We have found that the surface resistance of REBa2Cu3O7-x at 50 K and up to 9 T is lower than that of copper. This fact poses coated conductors as strong candidate to substitute copper as a beamscreen coating in CERN's future circular collider. To this end we have also analyzed the secondary electron yield (SEY) of REBa2Cu3O7-x and found a compatible coating made of sputtered Ti and amorphous carbon that decreases the SEY close to unity, a mandatory requirement for the beamscreen chamber of a circular collider in order to prevent the electron-cloud phenomenon.Peer ReviewedPostprint (author's final draft

RF characterisation of new coatings for future circular collider beam screens

For the future high energy colliders being under the design at this moment, the choice of a low surface impedance beam screen coating material has become of fundamental importance to ensure sufficiently low beam impedance and consequently guaranteed stable operation at high currents. We have studied the use of high-temperature superconducting coated conductors as possible coating materials for the beam screen of the FCC-hh. In addition, amorphous carbon coating and laser-based surface treatment techniques are effective surface treatments to lower the secondary electron yield and minimise the electron cloud build-up. We have developed and adapted different experimental setups based on resonating structures at frequencies below 10 GHz to study the response of these coatings and their modified surfaces under the influence of RF fields and DC magnetic fields up to 9¿T. Taking the FCC-hh as a reference, we will show that the surface resistance for REBCO-CCs is much lower than that of Cu. Further we show that the additional surface modifications can be optimised to minimise their impact on the surface impedance. Results from selected coatings will be presented.Work supported by CERN under Grants FCC-GOV-CC-0210 (KE4945/ATS), FCC-GOV-CC-0209 (KE4946/ATS) and FCC-GOV-CC0208 (KE4947/ATS). ICMAB funding through 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. UPC funding through the Unit of Excellence Maria de Maetzu MDM2016-0600. N. Tagdulang and A. Romanov acknowledge MSCA-COFUND-2016-754397 for the PhD grant.Peer ReviewedPostprint (published version

Coated conductor technology for the beamscreen chamber of future high energy circular colliders

The surface resistance of state-of-the-art REBa2Cu3O7-x coated conductors has been measured at 8 GHz versus temperature and magnetic field. We show that the surface resistance of REBa2Cu3O7-x strongly depends on the microstructure of the material. We have compared our results to those determined by the rigid fluxon model. The model gives a very good qualitative description of our data, opening the door to unravel the effect of material microstructure and vortex interactions on the surface resistance of high temperature superconductors. Moreover, it provides a powerful tool to design the best coated conductor architecture that minimizes the in-field surface resistance. We have found that the surface resistance of REBa2Cu3O7-x at 50 K and up to 9 T is lower than that of copper. This fact poses coated conductors as strong candidate to substitute copper as a beamscreen coating in CERN's future circular collider. To this end we have also analyzed the secondary electron yield (SEY) of REBa2Cu3O7-x and found a compatible coating made of sputtered Ti and amorphous carbon that decreases the SEY close to unity, a mandatory requirement for the beamscreen chamber of a circular collider in order to prevent the electron-cloud phenomenon.Peer Reviewe