SRF2023 - Table of Session: TUCXA (SRF Technology II)

Paper	Title	Page
TUCXA01	Study of the Dynamics of Flux Trapping in Different SRF Materials	380
	F. Kramer, S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany T. Kubo KEK, Ibaraki, Japan
	A dedicated experimental setup to measure magnetic flux dynamics and trapped flux in samples is used to precisely map out how trapped flux is influenced by different parameters. The setup allows for rapid thermal cycling of the sample so that effects of cooldown parameters can be investigated in detail. We show how temperature gradient, cooldown rate, and the magnitude of external field influence trapped flux in large grain, fine grain and coated niobium samples. The detailed measurements show unexpected results, namely that too fast cooldowns increase trapped flux, large grain material traps flux only when the external field is larger than a temperature gradient dependent threshold field, and the measured dependence of trapped flux on temperature gradient does not agree with an existing model. Therefore, a new model is presented which agrees better with the measured results.
	Slides TUCXA01 [3.180 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCXA01
About •	Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 June 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUCXA02	RF Vortex Nucleation in Superconductors within Time-Dependent Ginzburg-Landau Theory: Role of Surface Defects
	S.M. Anlage, C.Y. Wang UMD, College Park, Maryland, USA
	Funding: This work is funded by US Department of Energy / High Energy Physics through grant # DE-SC0017931 and the Maryland Quantum Materials Center. We use time-dependent Ginzburg-Landau (TDGL) numerical simulations to study the nucleation of RF vortices in Nb in the presence of surface defects when the material is subjected to an intense RF magnetic field in the GHz regime. In this work, we solve the TDGL equations, and Maxwell¿s equations, for a spatially nonuniform RF magnetic field created by a point RF magnetic dipole above the Nb surface. Here surface defects are notionally modeled as grain boundaries filled with a low-Tc impurity, such as oxidized Nb. The dynamics of RF currents induced in the resulting proximity-coupled superconductor are studied, and it is observed that RF vortex semi-loops penetrate the surface through the grain boundaries. Besides the RF vortex dynamics, the resulting third harmonic nonlinear response of the superconductor is calculated, and is shown to be closely related to RF vortex nucleation. The simulations show that RF vortex nucleation by surface defects can be studied by analyzing the third harmonic response of the superconductor. We make connections between these numerical studies and the results of our scanned near-field microwave microscopy efforts on a variety of SRF materials.
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Study of the Dynamics of Flux Trapping in Different SRF Materials

380

F. Kramer, S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany
T. Kubo
KEK, Ibaraki, Japan

A dedicated experimental setup to measure magnetic flux dynamics and trapped flux in samples is used to precisely map out how trapped flux is influenced by different parameters. The setup allows for rapid thermal cycling of the sample so that effects of cooldown parameters can be investigated in detail. We show how temperature gradient, cooldown rate, and the magnitude of external field influence trapped flux in large grain, fine grain and coated niobium samples. The detailed measurements show unexpected results, namely that too fast cooldowns increase trapped flux, large grain material traps flux only when the external field is larger than a temperature gradient dependent threshold field, and the measured dependence of trapped flux on temperature gradient does not agree with an existing model. Therefore, a new model is presented which agrees better with the measured results.

Slides TUCXA01 [3.180 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCXA01

About •

Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 June 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUCXA02

RF Vortex Nucleation in Superconductors within Time-Dependent Ginzburg-Landau Theory: Role of Surface Defects

S.M. Anlage, C.Y. Wang
UMD, College Park, Maryland, USA

Funding: This work is funded by US Department of Energy / High Energy Physics through grant # DE-SC0017931 and the Maryland Quantum Materials Center.
We use time-dependent Ginzburg-Landau (TDGL) numerical simulations to study the nucleation of RF vortices in Nb in the presence of surface defects when the material is subjected to an intense RF magnetic field in the GHz regime. In this work, we solve the TDGL equations, and Maxwell¿s equations, for a spatially nonuniform RF magnetic field created by a point RF magnetic dipole above the Nb surface. Here surface defects are notionally modeled as grain boundaries filled with a low-Tc impurity, such as oxidized Nb. The dynamics of RF currents induced in the resulting proximity-coupled superconductor are studied, and it is observed that RF vortex semi-loops penetrate the surface through the grain boundaries. Besides the RF vortex dynamics, the resulting third harmonic nonlinear response of the superconductor is calculated, and is shown to be closely related to RF vortex nucleation. The simulations show that RF vortex nucleation by surface defects can be studied by analyzing the third harmonic response of the superconductor. We make connections between these numerical studies and the results of our scanned near-field microwave microscopy efforts on a variety of SRF materials.

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)