SRF2023 - List of Authors (McMullin, M.W.)

Paper	Title	Page
MOPMB023	Magnetic Flux Expulsion in TRIUMF’s Multi-Mode Coaxial Cavities	135
SUSPB011	use link to see paper's listing under its alternate paper code
	R.R. Gregory, T. Junginger, M.W. McMullin UVIC, Victoria, Canada T. Junginger, P. Kolb, R.E. Laxdal, M.W. McMullin, Z.Y. Yao TRIUMF, Vancouver, Canada
	The external magnetic flux sensitivity of SRF cavities is an important characteristic of SRF accelerator design. Previous studies have shown that n-doped elliptical cavities are very sensitive to external fields, resulting in stringent requirements for residual field and cavity cool-down speed. Few such studies have been done on HWRs and QWRs. The impact of applied field direction and cool-down speed of flux expulsion for these cavities is poorly understood. This study explores the effect of these cool-down characteristics on TRIUMF¿s QWR using COMSOL ® simulations and experimental results. This study seeks to maximize the flux expulsion that occurs when a cavity is cooled down through its superconducting temperature. Flux expulsion is affected by the cool-down speed, temperature gradient, and orientation of the cavity relative to an applied magnetic field. It was found that for a vertically applied magnetic field the cool-down speed and temperature gradient did not have a significant effect on flux expulsion. Contrarily, a horizontal magnetic field can be nearly completely expelled by a fast, high temperature gradient cool-down.
	Poster MOPMB023 [2.191 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB023
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 30 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMB050	Thermal Feedback in Coaxial SRF Cavities	224
SUSPB020	use link to see paper's listing under its alternate paper code
	M.W. McMullin, P. Kolb, R.E. Laxdal, Z.Y. Yao TRIUMF, Vancouver, Canada T. Junginger UVIC, Victoria, Canada
	Funding: Natural Sciences and Engineering Research Council of Canada The phenomenon of Q-slope in SRF cavities is caused by a combination of thermal feedback and field-dependent surface resistance. There is currently no commonly accepted model of field-dependent surface resistance, and studies of Q-slope generally treat thermal feedback as a correction to whichever surface resistance model is being used. In the present study, we treat thermal feedback as a distinct physical effect whose effect on Q-slope is calculated using a novel finite-element code. We performed direct measurements of liquid helium pool boiling from niobium surfaces to obtain input parameters for the finite-element code. This code was used to analyze data from TRIUMF’s coaxial test cavity program, which has provided a rich dataset of Q-curves at temperatures between 1.7 K and 4.4 K at five different frequencies. Preliminary results show that thermal feedback makes only a small contribution to Q-slope at temperatures near 4.2 K, but has stronger effects as the bath temperature is lowered.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB050
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 August 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

MOPMB023

Magnetic Flux Expulsion in TRIUMF’s Multi-Mode Coaxial Cavities

135

SUSPB011

use link to see paper's listing under its alternate paper code

R.R. Gregory, T. Junginger, M.W. McMullin
UVIC, Victoria, Canada
T. Junginger, P. Kolb, R.E. Laxdal, M.W. McMullin, Z.Y. Yao
TRIUMF, Vancouver, Canada

The external magnetic flux sensitivity of SRF cavities is an important characteristic of SRF accelerator design. Previous studies have shown that n-doped elliptical cavities are very sensitive to external fields, resulting in stringent requirements for residual field and cavity cool-down speed. Few such studies have been done on HWRs and QWRs. The impact of applied field direction and cool-down speed of flux expulsion for these cavities is poorly understood. This study explores the effect of these cool-down characteristics on TRIUMF¿s QWR using COMSOL ® simulations and experimental results. This study seeks to maximize the flux expulsion that occurs when a cavity is cooled down through its superconducting temperature. Flux expulsion is affected by the cool-down speed, temperature gradient, and orientation of the cavity relative to an applied magnetic field. It was found that for a vertically applied magnetic field the cool-down speed and temperature gradient did not have a significant effect on flux expulsion. Contrarily, a horizontal magnetic field can be nearly completely expelled by a fast, high temperature gradient cool-down.

Poster MOPMB023 [2.191 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB023

About •

Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 30 July 2023

Cite •

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

MOPMB050

Thermal Feedback in Coaxial SRF Cavities

224

SUSPB020

use link to see paper's listing under its alternate paper code

M.W. McMullin, P. Kolb, R.E. Laxdal, Z.Y. Yao
TRIUMF, Vancouver, Canada
T. Junginger
UVIC, Victoria, Canada

Funding: Natural Sciences and Engineering Research Council of Canada
The phenomenon of Q-slope in SRF cavities is caused by a combination of thermal feedback and field-dependent surface resistance. There is currently no commonly accepted model of field-dependent surface resistance, and studies of Q-slope generally treat thermal feedback as a correction to whichever surface resistance model is being used. In the present study, we treat thermal feedback as a distinct physical effect whose effect on Q-slope is calculated using a novel finite-element code. We performed direct measurements of liquid helium pool boiling from niobium surfaces to obtain input parameters for the finite-element code. This code was used to analyze data from TRIUMF’s coaxial test cavity program, which has provided a rich dataset of Q-curves at temperatures between 1.7 K and 4.4 K at five different frequencies. Preliminary results show that thermal feedback makes only a small contribution to Q-slope at temperatures near 4.2 K, but has stronger effects as the bath temperature is lowered.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB050

About •

Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 August 2023

Cite •

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