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

Abstract

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.

High frequency response of thick REBCO coated conductors in the framework of the FCC study

“…An overview of all but one CCs' microstructure, film thickness and growth method is given in 11 . In additional to the CCs in 11 , a new CC is provided by Fujikura Ltd. with nominal I c − width(50 K) = 2 kA/cm − w and film thickness t = 2.5 µm , where Eu is used as the rare-earth with BaHfO 3 (BHO) nano rods in the REBCO matrix. All RF characterization is done on CCs whose Ag and Cu protection layers are stripped off.…”

“…Highly sensitive surface impedance measurements are performed with a high frequency, non-destructive, dielectric loaded resonator (DR) with resonant frequency . The resonator is based on the Hakki–Coleman geometry 14 , was previously used for non-linear characterization of HTS thin films 15 , 16 and has been redesigned as described in 11 , 17 in order to meet the sensitivity and geometrical requirements imposed by characterization of superconductors at cryogenic temperatures ( ) and up to in the bore of a PPMS from Quantum Design . The DR consists of a radiation shielding, cylindrical brass cavity terminated axially by interchangeable samples and loaded with a single crystal rutile (TiO2) disk ( and ), which is placed in the center of the cavity.…”

“…They are provided by Bruker HTS GmbH , Fujikura Ltd. , SuNAM Co. Ltd. , SuperOx , SuperPower Inc. and THEVA Dünnschichttechnik GmbH . An overview of all but one CCs’ microstructure, film thickness and growth method is given in 11 . In additional to the CCs in 11 , a new CC is provided by Fujikura Ltd. with nominal and film thickness , where Eu is used as the rare-earth with (BHO) nano rods in the REBCO matrix.…”

“…In order to avoid degradation of the superconductor, the metallic layers are either chemically etched right before measurements or the CCs are provided stripped by the manufacturer and stored in a low humidity environment. The error on measured surface resistances arising from deviations in rutile centering and inhomogeneities in CC tapes is estimated to be as discussed in 11 , while the uncertainty in the surface reactance is, in a first approximation, assumed to result from the the error on resonant frequency . In the following, CCs are regarded without their protection layers and named according to their manufacturer.…”

“…Our previous studies of six commercially available CCs have shown lower than thick Cu colaminated on stainless steel (equivalent of FCC beam screen) at and up to . In addition, we demonstrated compatibility with thin a-C layers to mitigate the secondary electron yield 11 . In this work, we extend the temperature range of measured surface resistances to .…”