TUOFDV —  Tuesday Oral Fundamental Development and Research   (29-Jun-21   08:20—11:10)
Paper Title Page
TUOFDV01
Dynamic Penetration Field of Vortices in a Superconductor Under RF Magnetic Field

ODU, Norfolk, Virginia, USA

Funding: This work was supported by DOE under grant No. DE-SC0010081.
We address the nonlinear dynamics of penetration of vortices in a superconductor subject to a periodic magnetic field H(t)=H0\sinω t parallel to the surface. The time-dependent Ginzburg-Landau equations for a gapped superconductor were simulated numerically to calculate the frequency and temperature dependencies of the field onset Hp(T,ω) of vortex penetration at T≈ Tc. It is shown that Hp(T,ω) can exceed the dc superheating field Hs at which the Meissner state becomes unstable. Here Hp(T,ω) increases with ω and approaches {2}Hs(T) at ωτ≥ 1, where τ(T) is the energy relaxation time of quasiparticles on phonons. We also investigated the effect of surface topographic defects on Hp(T,ω) and showed that they can substantially reduce Hp(T,ω) and cause additional power dissipation. Ultimately, we draw conclusions by comparing the results of our calculations with recent experimental measurements.

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TUOFDV02
Observation of Precise Distribution of Trapped Magnetic Flux Due to Quench by M&T Mapping System

Sokendai, Ibaraki, Japan
• E. Kako, M. Masuzawa, H. Sakai, R. Ueki, K. Umemori
KEK, Ibaraki, Japan
• P. Pizzol, A. Poudel, T. Tajima
LANL, Los Alamos, New Mexico, USA

This study focused on the flux trapping of the superconducting cavity by measuring changes in the spatial magnetic field distribution for the Nb single-cell cavity using the magnetic field and temperature mapping system. The different external magnetic fields were applied when the cavity was vertically tested. The differences of magnetic field distribution were compared before and after flux trapping caused by quenches. The magnetic field mapping measured the magnetic field, including 3 axial directions, outside the equator of the cavity. Moreover, the local heating generated by the magnetic flux trapping was observed locally using temperature mapping. The result shows that the changes in the magnetic field distribution have the magnetic field components towards the quench location. In this presentation, the detail of experiments and results of the change of the magnetic field distribution and the local heating will be presented.
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TUOFDV03 Vacancy-Hydrogen Dynamics and Magnetic Impurities During Mid-T Bake 342

• M. Wenskat, C. Bate, D. Reschke, J. Schaffran, L. Steder, H. Weise
DESY, Hamburg, Germany
• C. Bate, G.D.L. Semione, A. Stierle
University of Hamburg, Hamburg, Germany
• M. Butterling, E. Hirschmann, M.O. Liedke, A. Wagner
HZDR, Dresden, Germany
• J. Cizek
Charles University, Prague, Czech Republic
• W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Positron annihilation measurements allow to study the hydrogen interaction with vacancies in a crystal lattice. Furthermore, the 3/2 ratio of the positronium annihilation can be used to identify local magnetic impurities in thin layers. Dynamic studies of these properties in annealing studies up to 300°C will be presented. The discussion is accompanied by X-ray reflectivity studies performed on single crystal samples to study the niobium oxide dissolution. The dynamics of magnetic impurities during a Mid-T bake will be presented, put into the context of cavity studies and a potential link to rf properties will be discussed.
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUOFDV03
About • Received ※ 23 June 2021 — Revised ※ 12 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 05 December 2021
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TUOFDV04
Evidence of Reduced Magnetic Sensitivities in Low Beta SRF Cavities

• D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
• A. Miyazaki
Uppsala University, Uppsala, Sweden

Dedicated flux trapping experiments have been carried out on different types of low-beta superconducting accelerating cavities. The measured magnetic sensitivities of these complex geometries can be significantly lower than the predicted values calculated by commonly-used material-based models. In this paper, we suggest a new approach beyond the present material based models. Indeed, both the ambient magnetic field orientation and cavity geometry have a significant impact on the cavity performance degradation due to magnetic trapped flux. Experimental data are presented, and a new model to interpret the geometrical effect is introduced, assessed and shows as well very good agreement with data from the literature.
Slides TUOFDV04 [1.265 MB]
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TUOFDV05 Dynamics of RF Dissipation Probed via High-Speed Temperature Mapping 349

• R.D. Porter, N. Banerjee, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Recently, Cornell University has developed a new high-speed, high-resolution temperature mapping system that can resolve the time dynamics of RF dissipation, i.e., provide high-speed videos of the surface heating across the entire surface of the cavity. This new powerful tool allows to observe rapid changes in the local RF dissipation, as well as to resolve the dynamics of quenches, field emission processing, and other cavity events, giving new insights into these. This contribution presents the development of this new high-speed temperature mapping system, discusses its commissioning and extensive performance testing (e.g., demonstrating micro-Kelvin resolution), as well as show intriguing high-speed temperature mapping results from multiple Nb3Sn cavities.
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUOFDV05
About • Received ※ 01 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 06 February 2022
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TUOFDV06
Cavity Performance Limitations Understanding via SIMS Studies of Cavity Cutouts

• A.S. Romanenko
Fermilab, Batavia, Illinois, USA

The performance limitations of the modern SRF cavities are related to the near-surface cavity material structure, including the distribution of interstitial impurities such as hydrogen, oxygen, and nitrogen. The most direct way to connect the observed quality factors and achievable gradients to the material structure is to analyze the cavity cutouts using the most suitable analytical instruments and technique. In this contribution I will present the most recent insight gained from such studies using the state-of-the-art time of flight secondary ion mass spectroscopy (TOF-SIMS) on cutouts from the highest gradient-performing cavities, as well as the cavities prepared with the "mid-T" bake. The origins of the observed cavity behavior will be discussed.
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TUOFDV07 Sample Test Systems for Next-Gen SRF Surfaces 357

• T.E. Oseroff, M. Liepe, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

With the increasing worldwide focus on the development of new surfaces for SRF cavities, exploring alternative materials and multilayer structures, test systems that allow measuring the RF performance of simple sample geometries (e.g., flat samples) become increasingly essential. These systems provide RF performance results that are needed to guide the development of these surfaces. This contribution gives an overview of sample test systems currently available, including the improved Cornell sample host cavity. Recent advances in this important technology, performance specifications, and current limitations are discussed. In addition, an overview is given of interesting recent RF performance results on samples coated with non-niobium bulk and multilayer films.
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUOFDV07
About • Received ※ 08 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 05 September 2021
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TUOFDV08 First \betaNMR Results on SRF Samples at TRIUMF 365

• E. Thoeng, J.R. Adelman, A. Chatzichristos, M. Dehn, D. Fujimoto, V.L. Karner, R. Kiefl, W.A. MacFarlane, J.O. Ticknor
UBC & TRIUMF, Vancouver, British Columbia, Canada