SRF2019 - List of Authors (Guo, H.)

Paper	Title	Page
MOFAB4	Overview and SRF Requirements of the CiADS Project
	Y. He, Q. Chen, Z. Gao, H. Guo, G. Huang, Y.L. Huang, T.C. Jiang, C.L. Li, S.H. Liu, T. Tan, Y.Q. Wan, F.F. Wang, J.Q. Wu, W.M. Yue, B. Zhang, J.H. Zhang, S.H. Zhang, S.X. Zhang IMP/CAS, Lanzhou, People’s Republic of China J.P. Dai, F.S. He, Z.Q. Li, W.M. Pan IHEP, Beijing, People’s Republic of China T.C. Jiang University of Chinese Academy of Sciences, Beijing, People’s Republic of China
	Chinese initiative Accelerator Driven System started constructing in 2018. It consists a superconducting linac with 500 MeV and 5 mA; an LEB coolant fast reactor with 7.5 MW. The first beam coupling with reactor will be in 2024. The sc linac employed 5 families of superconducting resonators, two types of HWRs (β=0.1 and β=0.19), one type of double spokes (β=0.42) and two types of ellipticals (β=0.62 and β=0.82). The whole system will operate in 2 K. A space has been reserved for future upgrading to 1 GeV. As a demo of front-end of ADS, the CAFe (China ADS Front-end demo linac) has been developed and commissioned to verify the SRF techniques, high power CW beam and RAMI. 45 kW proton beam has been delivered to the dump and lasted more than 100 hours at the beginning of 2019. According to the operation experience, the challenge is the stability and performance of cavities under the heavy beam loading, some phenomenas have been observed. Up to now, the design of bulk Nb cavities have been finished and the prototype fabrication is on going. The techniques of Nb/Cu cavity and Nb₃Sn are also developed in IMP for the future project of ADS.
	Slides MOFAB4 [12.465 MB]
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MOP003	Development of Nb₃Sn Cavity Coating at IMP	21
	Z.Q. Yang, H. Guo, Y. He, C.L. Li, Z.Q. Lin, M. Lu, T. Tan, P.R. Xiong, S.H. Zhang, S.X. Zhang IMP/CAS, Lanzhou, People’s Republic of China
	The A15 superconductor Nb₃Sn is one of the most promising alternative materials to standard niobium for SRF applications. In this paper, we report our progress in the development of Nb₃Sn cavity coating by vapor diffusion method at IMP. The evolutionary process of nucleation was analyzed. Influence of S_nCl₂ partial pressure inhomogeneity was studied. Less-nuclear zones were found on the surfaces of nucleation samples. The Nb₃Sn film structure and composition were investigated and analyzed. In light of knowledge obtained above, the coating process was optimized. Finally, both 1.3 GHz and 650 MHz single cell cavities were coated and vertically tested both at 4 K and 2 K. Effect of low temperature baking (1000°C for 48 hs) on the RF performance of Nb₃Sn cavity was studied. After baking, the Q drop in the low field region was eliminated and the Q in the intermediate field region was increased 8 times. The Q was 10 times larger than that of the Nb cavity at 4.2 K even in the case of the ambient field larger than 20 mGs. This study shows that the low temperature baking is an effective enrichment to the post treatment of the Nb₃Sn cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP003
About •	paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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MOP085	The Destructive Effects to the RF Coupler by the Plasma Discharge	285
	A.D. Wu, Q.W. Chu, H. Guo, Y. He, S.C. Huang, T.C. Jiang, C.L. Li, Z.Q. Lin, F. Pan, Y.K. Song, T. Tan, W.M. Yue, S.H. Zhang, H.W. Zhao IMP/CAS, Lanzhou, People’s Republic of China
	The low temperature RF plasma was proved an effec-tive method to clean the niobium surface and relieve the field emission effect for the SRF cavities. In the case of half-wave resonators, these cavities were usually powered via the fundamental coupler with the electric coupling. Thus, coupler antennas were fixed in the intense electric field region, and this region was where the plasma rou-tinely ignited. Therefore, the ceramic window of coupler taken the risk of breakdown under the sputtering of ions and heating loads that may be caused by the plasma drift and diffusion from the electric field region. In this paper, the plasma ignition for surface cleaning on the HWR cavity and its coupler was investigated, and the power transmission, temperature raising and vacuum degradation were tested to characterize the adverse impacts on the ceramic window. Finally, the solution was proposed to figure these issues.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP085
About •	paper received ※ 22 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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TUP075	New Progress for Nb Sputtered 325 MHz QWR Cavities in IMP	621
	F. Pan, H. Guo, Y. He, T.C. Jiang, C.L. Li, M. Lu, T. Tan IMP/CAS, Lanzhou, People’s Republic of China
	Comparing with bulk niobium cavities, the Nb/Cu cavities feature a much better stability at 4.5 K. Last year, two 325 MHz QWR copper cavities coated with biased DC diode sputterred Nb for CiADS has been accomplished at IMP. But vertical tests showed the cavities had low Q₀ at 4 K. To solve the issue, a new coating system was designed and built. The sputtering target was redesigned and manufactured. The coating parameters were selected again and auxiliary heating was used to control the coating temperature in the process of sputtering. The power and Ar pressure during coating were also carefully selected. The paper covers resulting film characters, vertical tests with the evolution of the sputtering process, and improvements we made since last year.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP075
About •	paper received ※ 22 June 2019 paper accepted ※ 14 August 2019 issue date ※ 14 August 2019
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THP010	The Mechanism of Electropolishing of Niobium from Choline Chloride-based Deep Eutectic Solvents	852
	Q.W. Chu, H. Guo, S.C. Huang, A.D. Wu, Z.M. You IMP/CAS, Lanzhou, People’s Republic of China
	Funding: National Natural Science Foundation (11705252) The mechanism of electropolishing of niobium (Nb) from choline chloride-based deep eutectic solvent (DES) was studied by anodic polarization tests and electrochemical impedance spectroscopy (EIS) using a Nb rotating disk electrode (RDE). Based on the results of an anodic polarisation test, the electropolishing of Nb is mass transport controlled. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in this electrolyte. The influence of rotation rate, applied potential and electrolyte temperature on the electropolishing mechanism of Nb was investigated. As the applied potential positively shift, Rct, Rp and L increase, CPE decrease and Rs unchanged. The increase in rotation rate and electrolyte temperature leads to a decrease of Rs, Rct, Rp and L, and an increase of CPE.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP010
About •	paper received ※ 18 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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THP064	The Cryostat Results of Carbon Contamination and Plasma Cleaning for the Field Emission on the SRF Cavity	1038
	A.D. Wu, Q.W. Chu, H. Guo, Y. He, S.C. Huang, C.L. Li, F. Pan, Y.K. Song, T. Tan, P.R. Xiong, W.M. Yue, S.H. Zhang, H.W. Zhao IMP/CAS, Lanzhou, People’s Republic of China
	The field emission effect is the mainly limitation for the operating of SRF cavities in higher gradient with stability. In this paper, the experiments were performed to evaluate the impact of the carbon contaminants and plasma cleaning on the performance of SRF cavity. Contamination mechanism was classified into cryogenic adsorption with weak strength and chemical deposition with strong strength. For the weak strength condition, the methane was injected into the SRF cavity during vertical test to make a cryogenic adsorption layer on the inner surface of the cavity. The results revealed that the performance of SRF cavity degraded by methane physical adsorption, but the performance can be recovered by thermal cycle the cavity to 300K and pump methane out. For the strong strength condition, the chemical deposited dirty layer of carbon contamination was produced by using of Ar/CH₄ mixed PECVD method, and the SRF cavity performance was deteriorated by the severe field emission. Finally, carbon deposited cavity was treated by the Ar/O2 plasma, and its results revealed that the field emission removed greatly and the gradient was increased.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP064
About •	paper received ※ 20 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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FRCAB3	The Design of an Automated High-Pressure Rinsing System for SRF Cavity and the Outlook for Future Automated Cleanroom on Strings Assembly	1216
	H. Guo, Q.W. Chu, Y. He, C.L. Li, Y.K. Song, T. Tan, Z.M. You IMP/CAS, Lanzhou, People’s Republic of China
	High-pressure rinsing (HPR) and cavity assembly are two critical steps in cavity post-processing. Traditionally, high-pressure rinsing processing is based on ultra pure water system, pump, rinsing wand and simple-functional control system; cavity assembly processing is based on simple fixtures, wrenches, bolts and nuts. Beside the equipments, at least two operators are required in either of these two processing. Operators and their actions could bring mistakes and cause extra airborne particle contamination in cleanroom. To avoid the risk from labors, a robot has been introduced in IMP cleanroom for HPR assisting and assembly assisting. Labor cost and cavity RF test results are compared between the circumstances with and without robot assisting. In this work, an automated HPR system that has been designed and will be installed in IMP cleanroom will be presented. In addition, a future automated cleanroom on strings assembly will be discussed as well.
	Slides FRCAB3 [6.203 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-FRCAB3
About •	paper received ※ 03 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

MOFAB4

Overview and SRF Requirements of the CiADS Project

Y. He, Q. Chen, Z. Gao, H. Guo, G. Huang, Y.L. Huang, T.C. Jiang, C.L. Li, S.H. Liu, T. Tan, Y.Q. Wan, F.F. Wang, J.Q. Wu, W.M. Yue, B. Zhang, J.H. Zhang, S.H. Zhang, S.X. Zhang
IMP/CAS, Lanzhou, People’s Republic of China
J.P. Dai, F.S. He, Z.Q. Li, W.M. Pan
IHEP, Beijing, People’s Republic of China
T.C. Jiang
University of Chinese Academy of Sciences, Beijing, People’s Republic of China

Chinese initiative Accelerator Driven System started constructing in 2018. It consists a superconducting linac with 500 MeV and 5 mA; an LEB coolant fast reactor with 7.5 MW. The first beam coupling with reactor will be in 2024. The sc linac employed 5 families of superconducting resonators, two types of HWRs (β=0.1 and β=0.19), one type of double spokes (β=0.42) and two types of ellipticals (β=0.62 and β=0.82). The whole system will operate in 2 K. A space has been reserved for future upgrading to 1 GeV. As a demo of front-end of ADS, the CAFe (China ADS Front-end demo linac) has been developed and commissioned to verify the SRF techniques, high power CW beam and RAMI. 45 kW proton beam has been delivered to the dump and lasted more than 100 hours at the beginning of 2019. According to the operation experience, the challenge is the stability and performance of cavities under the heavy beam loading, some phenomenas have been observed. Up to now, the design of bulk Nb cavities have been finished and the prototype fabrication is on going. The techniques of Nb/Cu cavity and Nb₃Sn are also developed in IMP for the future project of ADS.

Slides MOFAB4 [12.465 MB]

Export •

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

MOP003

Development of Nb₃Sn Cavity Coating at IMP

21

Z.Q. Yang, H. Guo, Y. He, C.L. Li, Z.Q. Lin, M. Lu, T. Tan, P.R. Xiong, S.H. Zhang, S.X. Zhang
IMP/CAS, Lanzhou, People’s Republic of China

The A15 superconductor Nb₃Sn is one of the most promising alternative materials to standard niobium for SRF applications. In this paper, we report our progress in the development of Nb₃Sn cavity coating by vapor diffusion method at IMP. The evolutionary process of nucleation was analyzed. Influence of S_nCl₂ partial pressure inhomogeneity was studied. Less-nuclear zones were found on the surfaces of nucleation samples. The Nb₃Sn film structure and composition were investigated and analyzed. In light of knowledge obtained above, the coating process was optimized. Finally, both 1.3 GHz and 650 MHz single cell cavities were coated and vertically tested both at 4 K and 2 K. Effect of low temperature baking (1000°C for 48 hs) on the RF performance of Nb₃Sn cavity was studied. After baking, the Q drop in the low field region was eliminated and the Q in the intermediate field region was increased 8 times. The Q was 10 times larger than that of the Nb cavity at 4.2 K even in the case of the ambient field larger than 20 mGs. This study shows that the low temperature baking is an effective enrichment to the post treatment of the Nb₃Sn cavity.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP003

About •

paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

Export •

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

MOP085

The Destructive Effects to the RF Coupler by the Plasma Discharge

285

A.D. Wu, Q.W. Chu, H. Guo, Y. He, S.C. Huang, T.C. Jiang, C.L. Li, Z.Q. Lin, F. Pan, Y.K. Song, T. Tan, W.M. Yue, S.H. Zhang, H.W. Zhao
IMP/CAS, Lanzhou, People’s Republic of China

The low temperature RF plasma was proved an effec-tive method to clean the niobium surface and relieve the field emission effect for the SRF cavities. In the case of half-wave resonators, these cavities were usually powered via the fundamental coupler with the electric coupling. Thus, coupler antennas were fixed in the intense electric field region, and this region was where the plasma rou-tinely ignited. Therefore, the ceramic window of coupler taken the risk of breakdown under the sputtering of ions and heating loads that may be caused by the plasma drift and diffusion from the electric field region. In this paper, the plasma ignition for surface cleaning on the HWR cavity and its coupler was investigated, and the power transmission, temperature raising and vacuum degradation were tested to characterize the adverse impacts on the ceramic window. Finally, the solution was proposed to figure these issues.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP085

About •

paper received ※ 22 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

Export •

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

TUP075

New Progress for Nb Sputtered 325 MHz QWR Cavities in IMP

621

F. Pan, H. Guo, Y. He, T.C. Jiang, C.L. Li, M. Lu, T. Tan
IMP/CAS, Lanzhou, People’s Republic of China

Comparing with bulk niobium cavities, the Nb/Cu cavities feature a much better stability at 4.5 K. Last year, two 325 MHz QWR copper cavities coated with biased DC diode sputterred Nb for CiADS has been accomplished at IMP. But vertical tests showed the cavities had low Q₀ at 4 K. To solve the issue, a new coating system was designed and built. The sputtering target was redesigned and manufactured. The coating parameters were selected again and auxiliary heating was used to control the coating temperature in the process of sputtering. The power and Ar pressure during coating were also carefully selected. The paper covers resulting film characters, vertical tests with the evolution of the sputtering process, and improvements we made since last year.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP075

About •

paper received ※ 22 June 2019 paper accepted ※ 14 August 2019 issue date ※ 14 August 2019

Export •

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

THP010

The Mechanism of Electropolishing of Niobium from Choline Chloride-based Deep Eutectic Solvents

852

Q.W. Chu, H. Guo, S.C. Huang, A.D. Wu, Z.M. You
IMP/CAS, Lanzhou, People’s Republic of China

Funding: National Natural Science Foundation (11705252)
The mechanism of electropolishing of niobium (Nb) from choline chloride-based deep eutectic solvent (DES) was studied by anodic polarization tests and electrochemical impedance spectroscopy (EIS) using a Nb rotating disk electrode (RDE). Based on the results of an anodic polarisation test, the electropolishing of Nb is mass transport controlled. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in this electrolyte. The influence of rotation rate, applied potential and electrolyte temperature on the electropolishing mechanism of Nb was investigated. As the applied potential positively shift, Rct, Rp and L increase, CPE decrease and Rs unchanged. The increase in rotation rate and electrolyte temperature leads to a decrease of Rs, Rct, Rp and L, and an increase of CPE.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP010

About •

paper received ※ 18 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

Export •

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

THP064

The Cryostat Results of Carbon Contamination and Plasma Cleaning for the Field Emission on the SRF Cavity

1038

A.D. Wu, Q.W. Chu, H. Guo, Y. He, S.C. Huang, C.L. Li, F. Pan, Y.K. Song, T. Tan, P.R. Xiong, W.M. Yue, S.H. Zhang, H.W. Zhao
IMP/CAS, Lanzhou, People’s Republic of China

The field emission effect is the mainly limitation for the operating of SRF cavities in higher gradient with stability. In this paper, the experiments were performed to evaluate the impact of the carbon contaminants and plasma cleaning on the performance of SRF cavity. Contamination mechanism was classified into cryogenic adsorption with weak strength and chemical deposition with strong strength. For the weak strength condition, the methane was injected into the SRF cavity during vertical test to make a cryogenic adsorption layer on the inner surface of the cavity. The results revealed that the performance of SRF cavity degraded by methane physical adsorption, but the performance can be recovered by thermal cycle the cavity to 300K and pump methane out. For the strong strength condition, the chemical deposited dirty layer of carbon contamination was produced by using of Ar/CH₄ mixed PECVD method, and the SRF cavity performance was deteriorated by the severe field emission. Finally, carbon deposited cavity was treated by the Ar/O2 plasma, and its results revealed that the field emission removed greatly and the gradient was increased.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP064

About •

paper received ※ 20 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

Export •

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

FRCAB3

The Design of an Automated High-Pressure Rinsing System for SRF Cavity and the Outlook for Future Automated Cleanroom on Strings Assembly

1216

H. Guo, Q.W. Chu, Y. He, C.L. Li, Y.K. Song, T. Tan, Z.M. You
IMP/CAS, Lanzhou, People’s Republic of China

High-pressure rinsing (HPR) and cavity assembly are two critical steps in cavity post-processing. Traditionally, high-pressure rinsing processing is based on ultra pure water system, pump, rinsing wand and simple-functional control system; cavity assembly processing is based on simple fixtures, wrenches, bolts and nuts. Beside the equipments, at least two operators are required in either of these two processing. Operators and their actions could bring mistakes and cause extra airborne particle contamination in cleanroom. To avoid the risk from labors, a robot has been introduced in IMP cleanroom for HPR assisting and assembly assisting. Labor cost and cavity RF test results are compared between the circumstances with and without robot assisting. In this work, an automated HPR system that has been designed and will be installed in IMP cleanroom will be presented. In addition, a future automated cleanroom on strings assembly will be discussed as well.

Slides FRCAB3 [6.203 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-FRCAB3

About •

paper received ※ 03 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019

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