Paper | Title | Page |
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SATUT04 |
Materials Beyond Nb | |
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Thin film and multilayer are the promising way to go beyond the bulk niobium This lecture will introduce such film coated cavity developments and new other materials like Nb₃Sn, MgB₂, etc., except niobium. | ||
Slides SATUT04 [17.839 MB] | ||
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MOPMB041 | Microstructure Development in a Cold Worked SRF Niobium Sheet After Heat Treatments | 191 |
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Funding: Jefferson Science Associates, LLC under U.S. DOE Grant DEAC05-06OR23177, U.S. DOE, Office of HEP under Grant DE-SC0009960, and NHMFL through NSF Grant DMR-1644779 and the State of Florida. Bulk Nb for TESLA shaped SRF cavities is a mature technology. Significant advances are in order to push Q0’s to 1010-11(T= 2K), and involve modifications to the sub-surface Nb layers by impurity doping. In order to achieve the lowest surface resistance any trapped flux needs to be expelled for cavities to reach high Q0’s. There is clear evidence that cavities fabricated from polycrystalline sheets meeting current specifications require higher temperatures beyond 800 °C leads to better flux expulsion, and hence improves Q0. Recently, cavities fabricated with a non-traditional Nb sheet with initial cold work due to cold rolling expelled flux better after 800 °C/3h heat treatment than cavities fabricated using fine-grain poly-crystalline Nb sheets. Here, we analyze the microstructure development in Nb from the vendor supplied cold work non- annealed sheet that was fabricated into an SRF cavity as a function of heat treatment building upon the methodology development to analyze microstructure being developed by the FSU-MSU-UT, Austin-JLAB collaboration. The results indicate correlation between full recrystallization and better flux expulsion. |
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DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB041 | |
About • | Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 July 2023 | |
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MOPMB083 | Investigation of the Multilayer Shielding Effect through NbTiN-AlN Coated Bulk Niobium | 311 |
SUSPB025 | use link to see paper's listing under its alternate paper code | |
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We report measurements of the dc field onset Bp of magnetic flux penetration through NbTiN-AlN coating on bulk niobium using the Hall probe experimental setup. The measurements of Bp reveal the multilayer shielding effect on bulk niobium under high magnetic fields at cryogenic temperatures. We observed a significant enhancement in Bp for the NbTiN-AlN coated Nb samples as compared to bare Nb samples. The observed dependence of Bp on the coating thickness is consistent with theoretical predictions. | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB083 | |
About • | Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 12 August 2023 | |
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TUPTB019 | First Results from Nb₃Sn Coatings of 2.6 GHz Nb SRF Cavities Using DC Cylindrical Magnetron Sputtering System | 429 |
SUSPB047 | use link to see paper's listing under its alternate paper code | |
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Funding: Supported by DOE, Office of Accelerator R&D and Production, Contact No. DE-SC0022284, with partial support by DOE, Office of Nuclear Physics DE-AC05-06OR23177, Early Career Award to G. Eremeev. A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb₃Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 °C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb₃Sn phase and Nb (substrate). No peaks from any Nb-Sn compound other than Nb₃Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 µm thick Nb₃Sn. The first Nb₃Sn coated cavity reached close to Eacc = 8 MV/m, demonstrating a quality factor Q₀ of 3.2 × 108 at Tbath = 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q₀ was close to 1.1 × 109, dominated by the residual resistance, at 2 K and Eacc = 5 MV/m. The Nb₃Sn coated cavities demonstrated Tc in the range of 17.9 ¿ 18 K. Here we present the commissioning experience, system optimization, and the first results from the Nb₃Sn fabrication on flat samples and SRF cavities. |
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Poster TUPTB019 [1.216 MB] | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB019 | |
About • | Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 10 July 2023 | |
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WEIAA03 | Surface Roughness Reduction and Performance of Vapor-Diffusion Coating of Nb3Sn Film for SRF Application | 593 |
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Funding: This work is authored by Jefferson Science Associates LLC under U.S. DOE Contract No. DE-AC05- 06OR23177. Nb₃Sn offers the prospect of better RF performance (Q and Eacc) than niobium at any given temperature because of its superior superconducting properties. Nb₃Sn-coated SRF cavities are routinely produced by growing a few microns thick Nb₃Sn film on Nb cavities via tin vapor diffusion. It has been observed that a clean and smooth surface can enhance the performance of the Nb₃Sn-coated cavity, typically, the attainable acceleration gradient. The reduction of surface roughness is often linked with a correlative reduction in average coating thickness and grain size. Besides Sn supply’s careful tuning, the temperature profiles were varied to reduce the surface roughness as low as ~40 nm in 20 µm × 20 µm AFM scans, one-third that of the typical coating. Samples were systematically coated inside a mock single-cell cavity and examined using different material characterization techniques. A few sets of coating parameters were used to coat 1.3 GHz single-cell cavities to understand the effects of roughness variation on the RF performance. This presentation will discuss ways to reduce surface roughness with results from a systematic analysis of the samples and Nb₃Sn-coated single-cell cavities. |
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Slides WEIAA03 [7.231 MB] | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIAA03 | |
About • | Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 21 August 2023 | |
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WECAA01 | Progress in European Thin Film Activities | 607 |
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Funding: This project has received funding from the European Union s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. Thin-film cavities with higher Tc superconductors (SC) than Nb promise to move the operating temperature from 2 to 4.5 K with savings 3 orders of magnitude in cryogenic power consumption. Several European labs are coordinating their efforts to obtain a first 1.3 GHz cavity prototype through the I.FAST collaboration and other informal collaborations with CERN and DESY. R&D covers the entire production chain. In particular, new production techniques of seamless Copper and Niobium elliptical cavities via additive manufacturing are studied and evaluated. New acid-free polishing techniques to reduce surface roughness in a more sustainable way such as plasma electropolishing and metallographic polishing have been tested. Optimization of coating parameters of higher Tc SC than Nb (Nb₃Sn, V₃Si, NbTiN) via PVD and multilayer via ALD are on the way. Finally, rapid heat treatments such as Flash Lamp Annealing and Laser Annealing are used to avoid or reduce Cu diffusion in the SC film. The development and characterization of SC coatings is done on planar samples, 6 GHz cavities, choke cavities, QPR and 1.3 GHz cavities. This work presents the progress status of these coordinated efforts. |
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Slides WECAA01 [15.846 MB] | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WECAA01 | |
About • | Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 02 September 2023 — Issue date ※ 02 September 2023 | |
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WEIXA01 |
Experimental Evidence for Current Suppression in Superconducting Hetero Structures | |
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Coating Nb with thin layers of superconductors of higher penetration depth, than Nb have been proposed as a means of obtaining accelerating gradients (Eacc) of beyond Nb’s fundamental limit. Such heterostructures (which can also contain insulating layers between the superconductors) can potentially sustain their Meissner state above the superheating field, Bsh (of all the layers) due to the suppression of the Meissner screening current in the surface layer(s) induced by a counter-current in the substrate layer. We report evidence for counter-current flow in superconductor- superconductor (SS) Nb-Ti-N/Nb samples from depth-resolved measurements of their Meissner screening profiles at applied fields below or equal to 25 mT using the low energy muon spin rotation (LE-muSR) technique. Fits to the London model with appropriate boundary and continuity conditions determine the penetration depth of the Nb-Ti-N layers to be 182.5(31) nm in good agreement with literature values. Our results suggest that due to the strong suppression of the Meissner currents in the surface layer, multilayered structures of several superconducting and insulating layers are necessary to reach highest Eacc.
An electronic pre-print is available at https://arxiv.org/abs/2304.09360 |
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Slides WEIXA01 [0.623 MB] | ||
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WEPWB048 | Geometry Optimization for a Quadrupole Resonator at Jefferson Lab | 670 |
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Funding: This manuscript is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-6OR23177 with Jefferson Science Associates The quadrupole resonator (QPR) is a sample characterization tool to measure the RF properties of superconducting materials using the calorimetry method at different temperatures, magnetic fields, and frequencies. Such resonators are currently operating at CERN and HZB but suffer from Lorentz force detuning and modes overlapping, resulting in higher uncertainties in surface resistance measurement. Using the two CERN’s QPR model iterations, the geometry was optimized via electromagnetic and mechanical simulations to eliminate these issues. The new QPR version was modeled for an increasing range of magnetic fields. The magnetic field is concentrated at the center of the sample to reduce the uncertainty in surface resistance measurements significantly. This paper will discuss the QPR geometry optimization for the new version of QPR, which is now progressing towards fabrication. |
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DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB048 | |
About • | Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 21 August 2023 | |
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FRIXA02 |
SRF Thin Films: Not just for Cavities | |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Recent years have seen renewed interest and activities in developing SRF cavity materials based on thin film technologies. In this framework, considerable progress has been achieved in the development of high quality films and layered structures along with associated deposition techniques such as ECR, HiPIMS, and ALD. Beyond cavity applications, the developments in SRF thin film technologies find a variety of applications in the fields of superconducting metamaterials, electronics, sensors and quantum devices. High quality Nb films with high RRR open the way for enhanced coherence times for quantum qbits. Other SRF thin films such as NbTiN are developed for superconducting backend processes for future generations of computing hardware and radiation-hard sensors for nuclear and high-energy physics. The unifying theme across these technologies is that the same physics and material properties such as extreme low loss, stability, and manufacturability are required. This talk will present an overview of the emerging applications of SRF films and structures beyond accelerator cavities. |
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Slides FRIXA02 [6.385 MB] | ||
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