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

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 8 GHz and 50 K. We have employed a dielectric resonator to produce radio-frequency (RF) 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 future circular collider Hadron-Hadron (FCC-hh) at CERN We show that surface resistances in REBCO coated conductors without artificial pinning centers are more affected by a RF magnetic field than those containing nano-inclusions. Despite that, at 8 GHz, 50 K, and 9 T, most REBCO coated conductors studied outperform copper in terms of surface resistance, with the best sample having a 2.3 mΩ 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 16 T and 1 GHz, the actual FCC-hh dipole magnetic field, and the 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.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Thin Film (High Temperature) Superconducting Radiofrequency Cavities for the Search of Axion Dark Matter

5 pages, 6 figures. v2: minor updates after referee comments, matches published version in IEEEThe axion is a hypothetical particle which is a candidate for cold dark matter. Haloscope experiments directly search for these particles in strong magnetic fields with RF cavities as detectors. The Relic Axion Detector Exploratory Setup (RADES) at CERN in particular is searching for axion dark matter in a mass range above 30 $\mu$eV. The figure of merit of our detector depends linearly on the quality factor of the cavity and therefore we are researching the possibility of coating our cavities with different superconducting materials to increase the quality factor. Since the experiment operates in strong magnetic fields of 11 T and more, superconductors with high critical magnetic fields are necessary. Suitable materials for this application are for example REBa$_2$Cu$_3$O$_{7-x}$, Nb$_3$Sn or NbN. We designed a microwave cavity which resonates at around 9~GHz, with a geometry optimized to facilitate superconducting coating and designed to fit in the bore of available high-field accelerator magnets at CERN. Several prototypes of this cavity were coated with different superconducting materials, employing different coating techniques. These prototypes were characterized in strong magnetic fields at 4.2 K.This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 730871 (ARIES-TNA). BD and JG acknowledge funding through the European Research Council under grant ERC-2018-StG-802836 (AxScale). We also acknowledge funding via the Spanish Agencia Estatal de Investigacion (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under project PID2019- 108122GB-C33, and the grant FPI BES-2017-079787 (under project FPA2016-76978-C3-2-P). Furthermore we acknowledge support from SuMaTe RTI2018-095853-B-C21 from MICINN co-financed by the European Regional Development Fund, Center of Excellence award Severo Ochoa CEX2019- 000917-S and CERN under Grant FCCGOV-CC-0208 (KE4947/ATS).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

FCC-hh: The Hadron Collider Future Circular Collider Conceptual Design Report Volume 3

A. Abada et al.In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.Peer reviewe

Impact of high growth rates on the microstructure and vortex pinning of high-temperature superconducting coated conductors

High-temperature superconducting REBa2Cu3O7 (RE = rare earth or yttrium) coated conductors have emerged as a new class of materials with exceptional physical properties, such as very high critical currents and irreversibility field. Understanding the physics of vortices in these complex materials and controlling of the atomic structure of defects have made it possible to design their performance and achieve exceptional values of superconducting properties which enable their integration into devices. In order to improve performance and reduce costs, faster growth methods are now being explored, which raise new vortex physics scenarios. In this Technical Review, we distinguish the rich vortex pinning microstructure for vapour–solid, solid–solid and liquid–solid growth methods and how it is modified in the fast-growth process. The interplay between vortex physics and defect structure generated at high growth rates is addressed, as well as the implications of the electronic structure on vortex physics.We acknowledge the European Research Council for the ULTRASUPERTAPE project (ERC-2014-ADG-669504), IMPACT project (ERC-2019-PoC-8749) and SMS-INKS (ERC-2022- PoC-101081998), and EU COST actions OPERA (CA20116) and SUPERQUMAP (CA-21144). We also acknowledge the financial support from the Spanish Ministry of Science and Innovation and the European Regional Development Fund, MCIU/AEI/FEDER for SUPERENERTECH (PID2021–127297OB-C21), FUNFUTURE “Severo Ochoa” Program for Centers of Excellence in R&D (CEX2019–000917-S) and HTS-JOINTS (PDC2022–133208-I00) and PTI+TransEner CSIC programme for Spanish NGEU. The authors also thank the Catalan Government for 2021 SGR 00440. The access and staff support of several advanced facilities (Soleil and ALBA synchrotrons, INMA and ICN2 electron microscopes, ICMAB scientific services, NHMF Laboratory) are also acknowledged. Many discussions with academic and industrial colleagues and collaborators in the field of coated conductors and vortex pinning are acknowledged.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Quantification of the flux tubes and the stability of stripe pattern in the intermediate state of a type-1 superconducting film

The intermediate state in a type-1 superconducting Pb film is studied by using the scanning Hall probe microscopy, which shows quantized flux tubes with distinct flux density. The vorticity of flux tubes are quantified using the monopole model. It is found that the vorticity of the flux tubes can be tuned by using flux expulsion process under different magnetic field and temperatures. The stability of stipe patterns at high fields is studied with new stripe patterns formed after shaking with ah ac field. No flux tube is observed even after shaking with intense ac fields. All the results suggests the stripe patterns have very close energy, which is much favorable than the flux tube state. © 2014 Elsevier B.V. All rights reserved.status: publishe

Observation of single flux quantum vortices in the intermediate state of a type-I superconducting film

The flux quantization in the intermediate state of a type-I superconducting Pb film is studied by using scanning Hall probe microscopy. The vorticity of flux tubes can be tuned by changing the cooling field through the flux expulsion process, and single flux quantum vortices coexisting with multiple quantized flux tubes are observed at low enough fields. However, the minimum fluxoid observed through flux penetration is found to contain more than one flux quantum, and its vorticity increases with decreasing temperature. By combining these two processes it is possible to stabilize flux tubes of opposite polarity, and single flux quantum vortices are created through the annihilation process under the drive of the Lorentz force. Our results give strong evidence that single quantum vortices can be thermodynamically stabilized in the intermediate state of type-I superconductors. © 2013 American Physical Society.status: publishe

Vortex phase transition and isotropic flux dynamics in K0.8Fe2Se2 single crystal lightly doped with Mn

We have applied ac susceptibility measurements to study the vortex dynamics in a high quality K0.79Fe1.86Mn0.01Se 2 single crystal with applied magnetic field both parallel and perpendicular to the c-axis. The irreversibility line has been determined in the frequency range of 133 Hz-9777 Hz which can be well fitted using H irr = H0 (1-T/Tc)β with β = 1.49 for H ∥ c and β = 1.63 for H ∥ ab. The field dependence of the activation energy U0 is derived in the framework of thermally activated flux creep theory, yielding a power law dependence ∼ Hn with n ≈ - 0.58 for H below 0.75 T and n ≈ - 1 for H above 0.75 T. The derived activation energy U0 shows nearly isotropic behavior for both field directions and high values reaching 105 K at low fields. This observation points towards very strong intrinsic pinning in the investigated material, thus making KFeSe-systems promising for technical applications. © 2013 AIP Publishing LLC.status: publishe

In situ hydrostatic pressure induced improvement of critical current density and suppression of magnetic relaxation in Y(Dy-0.5)Ba2Cu3O7-(delta) coated conductors

We report on the effect of in situ hydrostatic pressure on the enhancement of the in-magneticfield critical current density parallel to the crystallographic c-axis and vortex pinning in epitaxial Y(Dy0.5)Ba2Cu3O7−δ coated conductors prepared by metal organic deposition. Our results show that in situ hydrostatic pressure greatly enhances the critical current density at high fields and high temperatures. At 80 K and 5 T we observe a ten-fold increase in the critical current density under the pressure of 1.2 GPa, and the irreversibility line is shifted to higher fields without changing the critical temperature. The normalized magnetic relaxation rate shows that vortex creep rates are strongly suppressed due to applied pressure, and the pinning energy is significantly increased based on the collective creep theory. After releasing the pressure, we recover the original superconducting properties. Therefore, we speculate that the in situ hydrostatic pressure exerted on the coated conductor enhances the pinning of existing extended defects. This is totally different from what has been observed in REBa2Cu3O7−δ melt-textured crystals, where the effect of pressure generates point-like defects

Bound vortex dipoles generated at pinning centres by Meissner current

One of the phenomena that make superconductors unique materials is the Meissner-Ochsenfeld effect. This effect results in a state in which an applied magnetic field is expelled from the bulk of the material because of the circulation near its surface of resistance-free currents, also known as Meissner currents. Notwithstanding the intense research on the Meissner state, local fields due to the interaction of Meissner currents with pinning centres have not received much attention. Here we report that the Meissner currents, when flowing through an area containing a pinning centre, generate in its vicinity two opposite sense current half-loops producing a bound vortex–antivortex pair, which eventually may transform into a fully developed vortex–antivortex pair ultimately separated in space. The generation of such vortex dipoles by Meissner currents is not restricted to superconductors; similar topological excitations may be present in other systems with Meissner-like phases.status: publishe

Two energy gaps in superconducting Lu2Fe3Si5 single crystal derived from the temperature dependence of lower critical field Hc1(T)

We report a detailed study of in-plane lower critical field H c1(T) and penetration depth λ ab(T) of the Lu 2Fe 3Si 5 superconductor. Two pronounced changes of the H c1 curvature are observed on the H c1(T) curve around 0.4T c and 0.65T c, respectively, which are attributed to the two-band nature of superconductivity in Lu 2Fe 3Si 5. The penetration depth of λ ab(T) follows a power law (∼T n) below 0.4T c, with n = 2.5 close to the values reported for the FeAs-pnictides, suggesting possible s ±-wave pairing in Lu 2Fe 3Si 5. Temperature dependence of H c1 can be well fitted by the two-gap BCS model in the full temperature region using two superconducting gaps Δ 1 = 0.19 ± 0.1 meV and Δ 2 = 1.02 ± 0.1 meV. © 2012 Elsevier B.V. All rights reserved.status: publishe