| Paper | Title | Page |
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| TUPOTK006 | Systematic Investigation of Flux Trapping Dynamics in Niobium Samples | 1200 |
| SUSPMF103 | use link to see paper's listing under its alternate paper code | |
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| Trapped magnetic flux in superconducting cavities can significantly increase surface resistance, and, thereby, limits the cavities’ performance. To reduce trapped flux in cavities, a better understanding of the fundamental mechanism of flux trapping is vital. We develop a new experimental design: measuring magnetic flux density at 15 points just above a niobium sheet of dimensions (100 x 60 x 3) mm with a time resolution of up to 2 ms and a flux resolution better than 0.5 µT. This setup allows us to control the temperature gradient and cooldown rate, both independently of each other, as well as the magnitude and direction of an external magnetic field. We present data gathered on a large-grain sample as well as on a fine-grain sample. Our data suggests that not only the temperature gradient but also the cooldown rate affects trapped flux. Additionally, we detect a non-trivial relationship between trapped flux and magnitude of applied field. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK006 | |
| About • | Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 16 June 2022 | |
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| TUPOTK005 | Mitigation of Parasitic Losses in the Quadrupole Resonator Enabling Direct Measurements of Low Residual Resistances of SRF Samples | 1196 |
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| The quadrupole resonator (QPR) is a dedicated sample-test cavity for the RF characterization of superconducting samples in a wide temperature, RF field and frequency range. Its main purpose are high resolution measurements of the surface resistance with direct access to the residual resistance thanks to the low frequency of the first operating quadrupole mode. Besides the well-known high resolution of the QPR, a bias of measurement data towards higher values has been observed, especially at higher harmonic quadrupole modes. Numerical studies show that this can be explained by parasitic RF losses on the adapter flange used to mount samples into the QPR. Coating several micrometer of niobium on those surfaces of the stainless steel flange that are exposed to the RF fields significantly reduced this bias, enabling a direct measurement of a residual resistance smaller than 5 nano-Ohm at 2 K and 413 MHz. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK005 | |
| About • | Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 28 June 2022 | |
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| TUPOTK016 | HiPIMS-Coated Novel S(I)S Multilayers for SRF Cavities | 1234 |
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Funding: Material syntheses and characterizations via SMART, BMBF, Germany (05K19PSA). Superconducting characterizations via iFAST, H2020, EU (101004730). Part of this work via the MNaF, University of Siegen. Pushing beyond the existing bulk niobium SRF cavities is indispensable along the path towards obtaining more sustainable next generation compact particle accelerators. One of the promising candidates to push the limits of the bulk niobium is thin film-based multilayer structures in the form of superconductor-insulator-superconductor (SIS). In this work, S(I)S multilayer structures were coated by high power impulse magnetron sputtering (HiPIMS), having industrial upscaling potential along with provid-ing higher quality films with respect to conventional magnetron sputtering techniques (e.g., DCMS), combined with (PE)-ALD techniques for deposition of the ex-situ insulating layers. On the path towards formulating opti-mized recipes for these materials to be coated on the inner walls of (S)RF cavities, the research focuses on innovat-ing the best performing S(I)S multilayer structures con-sisting of alternating superconducting thin films (e.g., NbN) with insulating layers of metal nitrides (e.g., AlN) and/or metal oxides (e.g., AlxOy) on niobium lay-ers/substrates (i.e., Nb/AlN/NbN) in comparison to the so-called SS multilayer structures (i.e., Nb/NbN). This con-tribution presents the initial materials and superconduct-ing and RF characterization results of the aforementioned multilayer systems on flat samples. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK016 | |
| About • | Received ※ 11 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 18 June 2022 | |
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| THPOST025 | Operational Experience with the Improved VSR DEMO Collimating Shielded Bellow in BESSY II | 2497 |
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Funding: Work supported by grants of the Helmholtz Association The Collimating Shielded Bellow (CsB) is designed to serve both as a flexible beam pipe connection between two adjacent superconducting cavities as foreseen in VSR DEMO and as a synchrotron light collimator to shield the down-stream cavity from synchrotron radiation. A convoluted inner RF shield was applied to prevent fundamental mode heating of the stainless-steel-made bellow in the cryogenic environment, making the such captured inner volume very difficult to access for inspection and cleaning. A first version of the device was successfully tested as part of the beam pipe of the synchrotron light source BESSY II under regular operation for more than a year. It suffered from an unfavorable long outgassing commissioning. Therefore a detachable design, allowing for rigorous inner surface preparation and cleaning, was built and recently installed in BESSY II. CsB version 2 design and experimental outcomes are described in the paper. First results indicated a significantly improved vacuum commissioning performance, which was confirmed later on. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOST025 | |
| About • | Received ※ 14 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 10 July 2022 | |
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| THPOST026 | Design of the Magnetic Shield for VSR DEMO | 2501 |
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Funding: Work supported by grants of the Helmholtz Association The VSR DEMO module, recently under development at HZB, will house two 4-cell 1.5 GHz superconducting RF cavities with a particularly powerful HOM damping scheme based on five waveguide HOM absorbers per cavity. A magnetic shield made of high-permeable material is needed around the cavities in order to prevent the ambient magnetic field exceeding very few µT thereby causing considerable unwanted RF losses. The shield needs to accommodate the waveguides, the fundamental power coupler, two beam pipes, two He feed / return lines, the tuner and the support structures, whilst being manufacturable and mountable. The paper discusses those difficulties and presents the matured magnetic shield design. Numerical simulations are used to evaluate the efficacy of the shield. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOST026 | |
| About • | Received ※ 14 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 22 June 2022 — Issue date ※ 22 June 2022 | |
| Cite • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |