| Paper | Title | Page |
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| MOP018 | Recent Results From Nb3Sn Single Cell Cavities Coated at Jefferson Lab | 65 |
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Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech Because of superior superconducting properties (Tc ~ 18.3K, Hs h ~ 425 mT and delta ~ 3.1 meV) compared to niobium, Nb3Sn promise better RF performance (Q0 and Eacc) and/or higher operating temperature (2 K Vs 4.2 K) for SRF cavities. Nb3Sn-coated SRF cavities are produced routinely by depositing a few micron-thick Nb3Sn films on the interior surface of Nb cavities via tin vapor diffusion technique. Early results from Nb3Sn cavities coated with this technique exhibited precipi-tous low field Q-slope, also known as Wuppertal slope. Several Nb3Sn single cell cavities coated at JLab ap-peared to exhibit similar Q-slope. RF testing of cavi-ties and materials study of witness samples were con-tinuously used to modify the coating protocol. At best condition, we were able to produce Nb3Sn cavity with Q0 in excess of ~ 5×1010 at 2 K and ~ 2×1010 at 4 K up the accelerating gradient of ~15 MV/m, without any significant Q-slope. In this presentation, we will dis-cuss recent results from several Nb3Sn coated single-cell cavities linked with material studies of witness samples, coating process modifications and the possi-ble causative factors to Wuppertal slope. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP018 | |
| About • | paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019 | |
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| TUP049 | Maximum Performance of Cavities Affected by the High-field Q-slope (HFQS) | 533 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The work of I. P. and A. G. is supported by NSF Grant PHY 100614-010. The performance of high-purity, bulk niobium SRF cavities treated by chemical processes such as BCP or EP is limited by the so-called high-field Q-slope (HFQS). Several models and experimental studies have been proposed and performed over the years to understand the origin of these anomalous losses but a general consensus on what these orgins are is yet to be established. In this contribution, we present the results from the RF tests of several 1.3 GHz single-cell cavities limited by the HFQS and tested using a variable input coupler. This allowed to maintain close to critical coupling even at high field and the data showed that the HFQS did not saturate and that in some cases a power dissipation of up to 200 W at 2 K could be sustained without quench. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP049 | |
| About • | paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019 | |
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| TUP050 | A Multi-layered SRF Cavity for Conduction Cooling Applications | 538 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Some of the work was supported by the 2008 PECASE Award of G. Ciovati. I. Parajuli is supported by NSF Grant PHYS-100614-010 Industrial application of SRF technology would favor the use of cryocoolers to conductively cool SRF cavities for particle accelerators, operating at or above 4.3 K. In order to achieve a lower surface resistance than Nb at 4.3 K, a superconductor with higher critical temperature should be used, whereas a metal with higher thermal conductivity than Nb should be used to conduct the heat to the cryocoolers. A standard 1.5 GHz bulk Nb single-cell cavity has been coated with a ~2 µm thick layer of Nb3Sn on the inner surface and with a 5 mm thick Cu layer on the outer surface for conduction cooled applications. The cavity performance has been measured at 4.3 K and 2.0 K in liquid He. The cavity reached a peak surface magnetic field of ~40 mT with a quality factor of 6×109 and 3.5×109 at 4.3 K, before and after applying the thick Cu layer, respectively. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP050 | |
| About • | paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019 | |
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| TUP052 | Design and Commissioning of a Magnetic Field Scanning System for SRF Cavities | 547 |
| SUSP031 | use link to see paper's listing under its alternate paper code | |
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Funding: Work supported by NSF Grant 100614-010. G. C. is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Trapped magnetic vortices are one of the leading sources of residual losses in SRF cavities. Mechanisms of flux pinning depend on the materials treatment and cool-down conditions. A magnetic field scanning system using flux-gate magnetometers and Hall probes has been designed and built to allow measuring the local magnetic field of trapped vortices normal to the outer surface of 1.3 GHz single-cell SRF cavities at cryogenic temperatures. Such system will allow inferring the key information about the distribution and magnitude of trapped flux in the SRF cavities for different material, surface preparations and cool-down conditions. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP052 | |
| About • | paper received ※ 22 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |