| Paper | Title | Page |
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| TUP082 | Materials Analysis of CED Nb Films Being Coated on Bulk Nb Single Cell SRF Cavities | 638 |
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Funding: This research is supported at AASC by DOE via Grant No. DE-FG02-08ER85162 and Grant No. DE-SC0004994 and by Jefferson Science Associates, LLC under U.S. DOE Contract No. DEAC05- 06OR23177 This study is an on-going research on depositing a Nb film on the internal wall of bulk Nb single cell SRF cavities, via an coaxial energetic condensation (CED) facility at AASC company. The motivation is to firstly create a homoepitaxy-like Nb/Nb film in a scale of a ~1.5GHz RF single cell cavity. Next, through SRF measurement and materials analysis, it might reveal the baseline properties of the CED-type homoepitaxy Nb films. Such knowledge of Nb-Nb homo-epitaxy is useful to create future realistic SRF cavity film coatings, such as hetero-epitaxy Nb/Cu Films, or template-layer-mitigated Nb films. One large-grain, and three fine grain bulk Nb cavity were coated. They went through cryogenic RF measurement. Preliminary results show that the Q0 of a Nb film at 2 K and low rf field, produced by CED, could be close to that of the pre-coated bulk Nb surface (being CBP'ed plus a light EP); but the quality drops rapidly for increasing rf field. We are investigating if the severe Q0-slope is caused by hydrogen incorporation before deposition, or is determined by some structural defects during Nb film growth. |
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| TUP083 | Film Deposition, Cryogenic RF Testing and Materials Analysis of a Nb/Cu Single Cell SRF Cavity | 642 |
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Funding: The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DEAC05- 06OR23177. In this study, we present preliminary results on using a cathodic-arc-discharge Nb plasma ion source to establish a Nb film-coated single-cell Cu cavity for SRF research. The polycrystalline Cu cavity was fabricated and mirror-surface-finished by a centrifugal barrel polishing (CBP) process at Jefferson Lab. Special pre-coating processes were conducted, in order to create a template-layer for follow-on Nb grain thickening. A sequence of cryogenic RF testing demonstrated that the Nb film does show superconductivity. But the quality factor of this Nb/Cu cavity is low as a result of high residual surface resistance. We are conducting a thorough materials characterization to explore if some microstructural defects or hydrogen impurities, led to such a low quality factor. |
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| TUP084 | Reciprocal Space XRD Mapping with Varied Incident Angle as a Probe of Structure Variation within Surface Depth | 651 |
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Funding: This research is supported at AASC by DOE via Grant No. DE-FG02-08ER85162 and Grant No. DE-SC0004994 and by Jefferson Science Associates, LLC under U.S. DOE Contract No. DEAC05- 06OR23177 In this study, we used a differential-depth X-Ray diffraction Reciprocal Spacing Mapping (XRD RSM) technique to investigate the crystal quality of a variety of SRF-relevant Nb film and bulk materials. By choosing different X-ray probing depths, the RSM study successfully revealed the materials’ microstructure evolutions after different materials processes, such as energetic condensation or surface polishing. The RSM data clearly measured the materials’ crystal quality at different thickness. Through a novel differential-depth RSM technique, this study found: I. for a heteroepitaxy Nb film Nb(100)/MgO(100), the film thickening process, via a cathodic arc-discharge Nb ion deposition, created a near-perfect single crystal Nb on the surface’s top-layer; II. for a mechanic polished single-crystal bulk Nb material, the microstructure on the top surface layer is more disordered than that in-grain. |
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