Thoeng Edward, Asaduzzaman Md, Kolb Philipp, McFadden Ryan M L, Morris Gerald D, Ticknor John O, Dunsiger Sarah R, Karner Victoria L, Fujimoto Derek, Junginger Tobias, Kiefl Robert F, MacFarlane W Andrew, Li Ruohong, Saminathan Suresh, Laxdal Robert E
TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3, Canada.
Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC, V6T 1Z1, Canada.
Sci Rep. 2024 Sep 14;14(1):21487. doi: 10.1038/s41598-024-71724-5.
We report direct measurements of the magnetic field screening at the limits of the Meissner phase for two superconducting niobium (Nb) samples. The samples are processed with two different surface treatments that have been developed for superconducting radio-frequency (SRF) cavity applications-a "baseline" treatment and an oxygen-doping ("O-doping") treatment. The measurements show: (1) that the screening length is significantly longer in the "O-doping" sample compared to the "baseline" sample; (2) that the screening length near the limits of the Meissner phase increases with applied field; (3) the evolution of the screening profile as the material transitions from the Meissner phase to the mixed phase; and (4) a demonstration of the absence of any screening profile for the highest applied field, indicative of the full flux entering the sample. Measurements are performed utilizing the -detected nuclear magnetic resonance ( -NMR) technique that allows depth resolved studies of the local magnetic field within the first 100 nm of the surface. The study takes advantage of the -SRF beamline, a new facility at TRIUMF, Canada, where field levels up to 200 mT are available parallel to the sample surface to replicate radio frequency fields near the Meissner breakdown limits of Nb.
我们报告了对两个超导铌（Nb）样品在迈斯纳相极限处的磁场屏蔽的直接测量结果。这些样品采用了两种不同的表面处理方法，这两种方法是为超导射频（SRF）腔应用而开发的——一种“基线”处理和一种氧掺杂（“O掺杂”）处理。测量结果表明：（1）“O掺杂”样品中的屏蔽长度比“基线”样品中的显著更长；（2）迈斯纳相极限附近的屏蔽长度随外加磁场增加；（3）随着材料从迈斯纳相转变为混合相，屏蔽轮廓的演变；（4）证明了在最高外加磁场下不存在任何屏蔽轮廓，这表明全磁通进入了样品。测量是利用μ子探测核磁共振（μ-NMR）技术进行的，该技术能够对表面前100nm内的局部磁场进行深度分辨研究。这项研究利用了加拿大TRIUMF的新设施μ-SRF光束线，在那里可提供高达200mT的与样品表面平行的场强，以复制接近Nb迈斯纳击穿极限的射频场。
