NAPAC2022 - List of Authors (Dhakal, P.)

Paper	Title	Page
WEZE5	Magnetic Flux Expulsion in Superconducting Radio-Frequency Niobium Cavities Made from Cold Worked Niobium	611
	B.D. Khanal ODU, Norfolk, Virginia, USA S. Balachandran, P.J. Lee NHMFL, Tallahassee, Florida, USA S. Chetri ASC, Tallahassee, Florida, USA P. Dhakal JLab, Newport News, Virginia, USA
	Trapped residual magnetic field during the cool down of superconducting radio frequency (SRF) cavities is one of the primary sources of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 to 100 µm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during the cool down, and hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and processed along with cavities made from SRF grade Nb. The flux expulsion and flux trapping sensitivity were measured after successive heat treatments in the range 800 to 1000°C. The flux expulsion from cold-worked fine-grain Nb cavities improves after 800°C/3h heat treatments and it becomes similar to that of standard fine-grain Nb cavities when the heat treatment temperature is higher than 900°C.
	Slides WEZE5 [2.029 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE5
About •	Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 31 August 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPA27	Effect of Duration of 120 °C Baking on the Performance of Superconducting Radio Frequency Niobium Cavities	683
	B.D. Khanal ODU, Norfolk, Virginia, USA P. Dhakal JLab, Newport News, Virginia, USA
	Over the last decade much attention was given in increasing the quality factor of superconducting radio frequency (SRF) cavities by impurity doping. Prior to the era of doping, the final cavity processing technique to achieve the high accelerating gradient includes the "in situ" low temperature baking of SRF cavities at temperature ~ 120°C for several hours. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low temperature baking at 120°C up to 96 hours. The experimental data were analyzed with available theory of superconductivity to elucidate the effect of the duration of low temperature baking on the superconducting properties of cavity materials as well as the RF performance. In addition, the RF loss related to the trapping of residual magnetic field refereed as flux trapping sensitivity was measured with respect to the duration of 120°C bake.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA27
About •	Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 19 August 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Magnetic Flux Expulsion in Superconducting Radio-Frequency Niobium Cavities Made from Cold Worked Niobium

611

B.D. Khanal
ODU, Norfolk, Virginia, USA
S. Balachandran, P.J. Lee
NHMFL, Tallahassee, Florida, USA
S. Chetri
ASC, Tallahassee, Florida, USA
P. Dhakal
JLab, Newport News, Virginia, USA

Trapped residual magnetic field during the cool down of superconducting radio frequency (SRF) cavities is one of the primary sources of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 to 100 µm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during the cool down, and hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and processed along with cavities made from SRF grade Nb. The flux expulsion and flux trapping sensitivity were measured after successive heat treatments in the range 800 to 1000°C. The flux expulsion from cold-worked fine-grain Nb cavities improves after 800°C/3h heat treatments and it becomes similar to that of standard fine-grain Nb cavities when the heat treatment temperature is higher than 900°C.

Slides WEZE5 [2.029 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE5

About •

Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 31 August 2022

Cite •

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

WEPA27

Effect of Duration of 120 °C Baking on the Performance of Superconducting Radio Frequency Niobium Cavities

683

B.D. Khanal
ODU, Norfolk, Virginia, USA
P. Dhakal
JLab, Newport News, Virginia, USA

Over the last decade much attention was given in increasing the quality factor of superconducting radio frequency (SRF) cavities by impurity doping. Prior to the era of doping, the final cavity processing technique to achieve the high accelerating gradient includes the "in situ" low temperature baking of SRF cavities at temperature ~ 120°C for several hours. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low temperature baking at 120°C up to 96 hours. The experimental data were analyzed with available theory of superconductivity to elucidate the effect of the duration of low temperature baking on the superconducting properties of cavity materials as well as the RF performance. In addition, the RF loss related to the trapping of residual magnetic field refereed as flux trapping sensitivity was measured with respect to the duration of 120°C bake.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA27

About •

Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 19 August 2022

Cite •

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