IPAC2015 - List of Authors (Reece, C.E.)

Paper	Title	Page
WEPWI016	Investigation of Differential Surface Removal due to Electropolishing at JLab	3525
	F. Marhauser, J. Follkie, C.E. Reece JLab, Newport News, Virginia, USA
	Surface chemistry carried out for Superconducting Radio Frequency (SRF) cavities such as Buffered Chemical Polishing (BCP) and Electropolishing (EP) aims to uniformly remove the internal surface of a cavity along the entire structure and within each cell from equator to iris in order to obtain an equally etched surface. A uniform removal however is not readily achievable due to the complex fluid flow and varying temperatures of the acid mixture, which can lead to differential etching. This needs to be considered when envisaging a certain surface damage removal throughout the interior. The process-specific differential etching influences the target frequency set at the manufacturing stage as well as the field flatness and length of the as-built cavity. We report on analyses of JLab's present EP system using experimental data for six nine-cell cavities that have been processed recently in the frame of the LCLS-II high-Q development plan. In conjunction with numerical simulations, the differential etching and the impact on field flatness is assessed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI016
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WEPWI019	Quench Studies of Six High Temperature Nitrogen Doped 9 Cell Cavities for Use in the LCLS-II Baseline Prototype Cryo-module at Jefferson Laboratory	3528
	A.D. Palczewski, G.V. Eremeev, R.L. Geng, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Jefferson Lab (JLab) processed six nine-cell cavities as part of a small-scale production for LCLS-II cavity processing development utilizing the promising nitrogen-doping process. [1] Various nitrogen-doping recipes have been scrutinized to optimize process parameters with the aim to guarantee an unloaded quality factor (Q 0) of 2.7·10¹⁰ at an accelerating field (Eacc) of 16 MV/m at 2.0 K in the cryomodule. During the R&D phase the characteristic Q0 vs. Eacc performance curve of the cavities has been measured in JLab’s vertical test area at 2 K. The findings showed the characteristic rise of the Q0 with Eacc as expected from nitrogen-doping. Initially, five cavities achieved an average Q0 of 3.3·10¹⁰ at the limiting Eacc averaging to 16.8 MV/m, while one cavity experienced an early quench accompanied by an unusual Q 0 vs. Eacc curve. The project accounts for a cavity performance loss from the vertical dewar test (with or without the helium vessel) to the horizontal performance in a cryomodule, such that these results leave no save margin to the cryomodule specification. Consequently, a refinement of the nitrogen-doping has been initiated to guarantee an average quench field above 20 MV/m without impeding the Q 0. This paper covers the refinement work performed for each cavity, which depends on the initial results, as well as a quench analysis carried out before and after the rework during the vertical RF tests as far as applicable.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI019
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WEPWI021	An Analysis of the Temperature and Field Dependence of the RF Surface Resistance of Nitrogen-Doped Niobium SRF Cavities with Respect to Existing Theoretical Models	3532
	C.E. Reece, A.D. Palczewski JLab, Newport News, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 Recent progress with the reduction of rf surface resistance (Rs) of niobium SRF cavities via the use of high temperature surface doping by nitrogen has opened a new regime for energy efficient accelerator applications. For particular doping conditions one observes dramatic decreases in Rs with increasing surface magnetic fields. The observed variations as a function of temperature may be analyzed in the context of recent theoretical treatments in hopes of gaining insight into the underlying beneficial mechanism of the nitrogen treatment. Systematic data sets of Q0 vs. Eacc vs. temperature acquired during the high Q0 R&D work of the past year will be compared with theoretical model predictions. * * B. P. Xiao et al., Physica C: Superconductivity 490 (0), 26-31 (2013) and A. Gurevich, PRL 113 (8), 087001 (2014)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI021
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Paper

Title

Page

Investigation of Differential Surface Removal due to Electropolishing at JLab

3525

F. Marhauser, J. Follkie, C.E. Reece
JLab, Newport News, Virginia, USA

Surface chemistry carried out for Superconducting Radio Frequency (SRF) cavities such as Buffered Chemical Polishing (BCP) and Electropolishing (EP) aims to uniformly remove the internal surface of a cavity along the entire structure and within each cell from equator to iris in order to obtain an equally etched surface. A uniform removal however is not readily achievable due to the complex fluid flow and varying temperatures of the acid mixture, which can lead to differential etching. This needs to be considered when envisaging a certain surface damage removal throughout the interior. The process-specific differential etching influences the target frequency set at the manufacturing stage as well as the field flatness and length of the as-built cavity. We report on analyses of JLab's present EP system using experimental data for six nine-cell cavities that have been processed recently in the frame of the LCLS-II high-Q development plan. In conjunction with numerical simulations, the differential etching and the impact on field flatness is assessed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI016

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

WEPWI019

Quench Studies of Six High Temperature Nitrogen Doped 9 Cell Cavities for Use in the LCLS-II Baseline Prototype Cryo-module at Jefferson Laboratory

3528

A.D. Palczewski, G.V. Eremeev, R.L. Geng, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Jefferson Lab (JLab) processed six nine-cell cavities as part of a small-scale production for LCLS-II cavity processing development utilizing the promising nitrogen-doping process. [1] Various nitrogen-doping recipes have been scrutinized to optimize process parameters with the aim to guarantee an unloaded quality factor (Q 0) of 2.7·10¹⁰ at an accelerating field (Eacc) of 16 MV/m at 2.0 K in the cryomodule. During the R&D phase the characteristic Q0 vs. Eacc performance curve of the cavities has been measured in JLab’s vertical test area at 2 K. The findings showed the characteristic rise of the Q0 with Eacc as expected from nitrogen-doping. Initially, five cavities achieved an average Q0 of 3.3·10¹⁰ at the limiting Eacc averaging to 16.8 MV/m, while one cavity experienced an early quench accompanied by an unusual Q 0 vs. Eacc curve. The project accounts for a cavity performance loss from the vertical dewar test (with or without the helium vessel) to the horizontal performance in a cryomodule, such that these results leave no save margin to the cryomodule specification. Consequently, a refinement of the nitrogen-doping has been initiated to guarantee an average quench field above 20 MV/m without impeding the Q 0. This paper covers the refinement work performed for each cavity, which depends on the initial results, as well as a quench analysis carried out before and after the rework during the vertical RF tests as far as applicable.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI019

Export •

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

WEPWI021

An Analysis of the Temperature and Field Dependence of the RF Surface Resistance of Nitrogen-Doped Niobium SRF Cavities with Respect to Existing Theoretical Models

3532

C.E. Reece, A.D. Palczewski
JLab, Newport News, Virginia, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177
Recent progress with the reduction of rf surface resistance (Rs) of niobium SRF cavities via the use of high temperature surface doping by nitrogen has opened a new regime for energy efficient accelerator applications. For particular doping conditions one observes dramatic decreases in Rs with increasing surface magnetic fields. The observed variations as a function of temperature may be analyzed in the context of recent theoretical treatments in hopes of gaining insight into the underlying beneficial mechanism of the nitrogen treatment. Systematic data sets of Q0 vs. Eacc vs. temperature acquired during the high Q0 R&D work of the past year will be compared with theoretical model predictions. *
* B. P. Xiao et al., Physica C: Superconductivity 490 (0), 26-31 (2013) and
A. Gurevich, PRL 113 (8), 087001 (2014)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI021

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