SRF2017 - List of Keywords (ECR)

Paper	Title	Other Keywords	Page
MOPB007	Design of the Superconducting Quarter Wave Resonators for HIAF	ion, cavity, linac, heavy-ion	59
	C. Zhang, L. Chen, Q.W. Chu, H. Guo, Y. He, S.C. Huang, Y.L. Huang, T.C. Jiang, L. Li, Y.M. Li, F. Pan, T. Tan, R.X. Wang, A.D. Wu, Q.J. Wu, P.R. Xiong, W.M. Yue, S.H. Zhang, S.X. Zhang IMP/CAS, Lanzhou, People's Republic of China
	A heavy ion accelerator facility (HIAF) is under development in the Institute of Modern Physics. For the low energy superconducting accelerating section, two types of quarter wave resonators with frequency of 81.25 MHz and β of 0.05 and 0.10 have been proposed. The electro-magnetic design has been optimized in order to reach the high accelerating voltage, and the optimization also included the drift tube face tilting to compensate for the beam steering caused by the asymmetry in the quarter wave resonator geometry.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB007
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MOPB089	Characterisation of Magnetic Shielding Material for HL-LHC Crab Cavities	ion, cavity, cryogenics, shielding	273
	K. Eiler, P. Arpaia, M.C.L. Buzio, O. Capatina, S.A.E. Langeslag, A. Parrella CERN, Geneva, Switzerland P. Arpaia, A. Parrella Naples University Federico II, Science and Technology Pole, Napoli, Italy A. Parrella IT, Lisboa, Portugal N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: CERN, 1211 Geneva 23 To guarantee optimum performance, the crab cavities for the high-luminosity upgrade of CERN's LHC need to be shielded from external magnetic fields. Consequently, they will be enclosed by two layers of magnetic shielding, of which the inner is immersed in superfluid helium at 2 K. A Ni-based high-permeability material with a tailored composition and a designated heat treatment is applied. Its magnetic properties at cryogenic temperature are however not yet fully assessed. Especially the effect of deformation on magnetic properties has not been thoroughly investigated, however strain effects may have severe consequences. A magnetic measurement set-up has been developed, and the magnetic permeability at room temperature and at cryogenic temperatures is evaluated, showing that the maximum relative permeability at 4 K exceeds the design criteria of 100, 000. Measurements of the magnetic permeability after introduction of uniaxial plastic deformation between 0% and 3% are conducted by means of an Epstein frame. Results show that deformation induces significant decrease of the magnetic performance, underlining that particular care must be taken during all stages of handling and operation. *konrad.eiler@cern.ch
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB089
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TUYAA02	Advancement in the Understanding of the Field and Frequency Dependent Microwave Surface Resistance of Niobium	ion, cavity, niobium, resonance	364
	M. Martinello, S. Aderhold, S.K. Chandrasekaran, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	The radio-frequency surface resistance of niobium resonators is incredibly reduced when nitrogen impurities are dissolved as interstitial in the material, conferring ultra-high Q-factors at medium values of accelerating field. This effect has been observed in both high and low temperature nitrogen treatments. As a matter of fact, the peculiar anti Q-slope observed in nitrogen doped cavities, i.e. the decreasing of the Q-factor with the increasing of the radio-frequency field, come from the decreasing of the BCS surface resistance component as a function of the field. Such peculiar behavior has been considered consequence of the interstitial nitrogen present in the niobium lattice after the doping treatment. The study here presented show the field dependence of the BCS surface resistance surface of cavities with different resonant frequencies, such as: 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 GHz, and processed with different state-of-the-art surface treatments. These findings show for the first time that the anti Q-slope might be seen at high frequency even for clean Niobium cavities, revealing useful suggestion on the physics underneath the anti Q-slope effect. *M. Martinello, A. Grassellino, M. Checchin, A. Romanenko, O. Melnychuk, D.A. Sergatskov, S. Posen, J. Zasadzinski App. Phys. Lett. 109, 6 (2016)
	Slides TUYAA02 [4.342 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYAA02
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TUPB009	High-frequency SRF Cavities	cavity, ion, cryogenics, SRF	400
	T.E. Oseroff, D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Historically, the frequency of SRF cavities has been limited by cryogenic power dissipation increasing rapidly with frequency, due to the BCS surface resistance having a quadratic dependence on frequency. Now, new SRF surfaces using doped niobium and compound superconductors like Nb3Sn can drastically reduce the BCS part of the surface resistance. The temperature independent part of the surface resistance (residual resistance) can therefore become dominant, and has its own, different frequency dependence. We have developed a model to analyze cryogenic cooling power requirements for SRF cavities as function of operating frequency, temperature, and trapped flux to evaluate the impact of the novel low-loss SRF surfaces on the questions of optimal operating frequency and frequency limit. We show that high-frequency SRF cavities now become a realistic option for future SRF driven accelerators. As the transverse cavity size decreases inversely with respect to its resonant frequency, such high-frequency SRF cavities could greatly reduce cost.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB009
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TUPB039	Electropolishing of Niobium from Deep Eutectic Solvents Based on Choline Chloride	ion, cavity, niobium, SRF	475
	Q.W. Chu, H. Guo, Y. He, L. Li, P.R. Xiong, Z.M. You, S.H. Zhang IMP/CAS, Lanzhou, People's Republic of China
	Niobium (Nb) was successfully electropolished from a green ionic liquid, choline chloride/urea deep eutectic solvent (DES). This paper was to investigate the influence of various electropolishing parameters, including electropolishing time, temperature and voltage, on the electropolishing rate, surface roughness, glossiness and microstructure of Nb. The result showed that the electropolishing parameters had a significant impact on the performance of Nb. Based on surface analysis by scanning electron microscope (SEM) and atomic force microscope (AFM), smooth Nb can be achieved under properly controlled conditions.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB039
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TUPB111	R&D Activities on Centrifugal Barrel Polishing of 1.3 GHz Niobium Cavities at DESY/University of Hamburg	ion, cavity, niobium, laser	655
	A.L. Prudnikava, B. Foster, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany A. Ermakov, B. Foster DESY, Hamburg, Germany Y. Tamashevich HZB, Berlin, Germany
	In this paper the status of research activities at ILC-HiGrade Lab (DESY/University of Hamburg) on Centrifugal Barrel Polishing (CBP) of 1.3 GHz Niobium Cavities is presented. We focus on CBP based on the polishing recipe reported by Fermi National Laboratory and Jefferson Lab. The aim is to gain a better understanding of the limitations of this technique, detailed characterization of the treated surface after each polishing step using a "coupon" single cell cavity. Plastic deformations upon initial CBP steps, embedded polishing media and residual damage upon final polishing were investigated at different areas of the cavity. C. A. Cooper, L. D. Cooley, Supercond. Sci. Technol. 26 (2013) 015011
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB111
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THPB019	Simulation of the Thermoelectrically Generated Magnetic Field in a SC Nine-cell Cavity	ion, cavity, simulation, experiment	771
	J.M. Köszegi, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Several studies showed that thermocurrents generate a magnetic field in a horizontal cavity test assembly or cryomodul, which may get trapped during the superconducting phase transition. The trapped flux causes additional dissipation during operation and can therefore significantly degrade the cavity's quality factor. We simulated the distribution of the generated magnetic field for different temperature distributions and compared the results to experimental findings. Furthermore, the impact of a growing superconducting area was investigated. The simulations complement the experimental studies because measurements were only feasible with a limited number of probes and restricted to selected locations and orientations. The simulations allow to analyze this data in the context of the whole system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB019
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THPB037	Cavity Fundamental Mode and Beam Interaction in CEPC Main Ring	ion, cavity, beam-loading, luminosity	825
	D.J. Gong, J. Gao, D. Wang, J.Y. Zhai IHEP, Beijing, People's Republic of China
	Circular electron positron collider (CEPC) is design as a particle factory for Higgs, W and Z. The preliminary study is undertaken for CEPC cavity fundamental mode and beam interaction in this paper. The baseline of CEPC is DR scheme, the alternative is the APDR scheme. Beam loading effects and the corresponding longitudinal beam dynamics of both CEPC DR and APDR are elaborated in this article. The phase shift and voltage decrease are calculated by the analytic formula and the program. Furthermore, the longitudinal coupled-bunch instability is also studied. At last, the RF parameters are calculated for CEPC 100km APDR, in order to match the machine parameters and relieve the beam loading effects.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB037
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THPB061	Effect Of Dislocations On the Thermal Conductivity Of Superconducting Nb	ion, scattering, electron, cavity	886
	P. Xu, N.T. Wright MSU, East Lansing, Michigan, USA T.R. Bieler Michigan State University, East Lansing, Michigan, USA
	Funding: This work is funded by DOE and OHEP through grant number DE-FOA-0001438. The thermal conductivity of Niobium (Nb) often experiences a local maximum (a phonon peak) at a temperature between 1.8 and 3 K. While the magnitude of the phonon peak has been shown to be related to the dislocation density and may be influenced by manufacturing processes, little has been discussed as to the temperature at which the peak occurs. In examining these phenomena, it has been determined that more explicit accounting of phonon–dislocation scattering in a popular model better represents the thermal conductivity at temperatures colder than 3 K. Scaled sensitivity coefficients show this term to have similar influence as the phonon-electron and phonon-boundary scattering terms. Results using the enhanced model also show an apparent threshold of dislocation density below which there is little contribution to the thermal conductivity of Nb.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB061
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Paper

Title

Other Keywords

Page

MOPB007

Design of the Superconducting Quarter Wave Resonators for HIAF

ion, cavity, linac, heavy-ion

59

C. Zhang, L. Chen, Q.W. Chu, H. Guo, Y. He, S.C. Huang, Y.L. Huang, T.C. Jiang, L. Li, Y.M. Li, F. Pan, T. Tan, R.X. Wang, A.D. Wu, Q.J. Wu, P.R. Xiong, W.M. Yue, S.H. Zhang, S.X. Zhang
IMP/CAS, Lanzhou, People's Republic of China

A heavy ion accelerator facility (HIAF) is under development in the Institute of Modern Physics. For the low energy superconducting accelerating section, two types of quarter wave resonators with frequency of 81.25 MHz and β of 0.05 and 0.10 have been proposed. The electro-magnetic design has been optimized in order to reach the high accelerating voltage, and the optimization also included the drift tube face tilting to compensate for the beam steering caused by the asymmetry in the quarter wave resonator geometry.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB007

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MOPB089

Characterisation of Magnetic Shielding Material for HL-LHC Crab Cavities

ion, cavity, cryogenics, shielding

273

K. Eiler, P. Arpaia, M.C.L. Buzio, O. Capatina, S.A.E. Langeslag, A. Parrella
CERN, Geneva, Switzerland
P. Arpaia, A. Parrella
Naples University Federico II, Science and Technology Pole, Napoli, Italy
A. Parrella
IT, Lisboa, Portugal
N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

Funding: CERN, 1211 Geneva 23
To guarantee optimum performance, the crab cavities for the high-luminosity upgrade of CERN's LHC need to be shielded from external magnetic fields. Consequently, they will be enclosed by two layers of magnetic shielding, of which the inner is immersed in superfluid helium at 2 K. A Ni-based high-permeability material with a tailored composition and a designated heat treatment is applied. Its magnetic properties at cryogenic temperature are however not yet fully assessed. Especially the effect of deformation on magnetic properties has not been thoroughly investigated, however strain effects may have severe consequences. A magnetic measurement set-up has been developed, and the magnetic permeability at room temperature and at cryogenic temperatures is evaluated, showing that the maximum relative permeability at 4 K exceeds the design criteria of 100, 000. Measurements of the magnetic permeability after introduction of uniaxial plastic deformation between 0% and 3% are conducted by means of an Epstein frame. Results show that deformation induces significant decrease of the magnetic performance, underlining that particular care must be taken during all stages of handling and operation.
*konrad.eiler@cern.ch

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB089

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

TUYAA02

Advancement in the Understanding of the Field and Frequency Dependent Microwave Surface Resistance of Niobium

ion, cavity, niobium, resonance

364

M. Martinello, S. Aderhold, S.K. Chandrasekaran, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

The radio-frequency surface resistance of niobium resonators is incredibly reduced when nitrogen impurities are dissolved as interstitial in the material, conferring ultra-high Q-factors at medium values of accelerating field. This effect has been observed in both high and low temperature nitrogen treatments. As a matter of fact, the peculiar anti Q-slope observed in nitrogen doped cavities, i.e. the decreasing of the Q-factor with the increasing of the radio-frequency field, come from the decreasing of the BCS surface resistance component as a function of the field. Such peculiar behavior has been considered consequence of the interstitial nitrogen present in the niobium lattice after the doping treatment. The study here presented show the field dependence of the BCS surface resistance surface of cavities with different resonant frequencies, such as: 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 GHz, and processed with different state-of-the-art surface treatments. These findings show for the first time that the anti Q-slope might be seen at high frequency even for clean Niobium cavities, revealing useful suggestion on the physics underneath the anti Q-slope effect.
*M. Martinello, A. Grassellino, M. Checchin, A. Romanenko, O. Melnychuk, D.A. Sergatskov, S. Posen, J. Zasadzinski App. Phys. Lett. 109, 6 (2016)

Slides TUYAA02 [4.342 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYAA02

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TUPB009

High-frequency SRF Cavities

cavity, ion, cryogenics, SRF

400

T.E. Oseroff, D.L. Hall, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Historically, the frequency of SRF cavities has been limited by cryogenic power dissipation increasing rapidly with frequency, due to the BCS surface resistance having a quadratic dependence on frequency. Now, new SRF surfaces using doped niobium and compound superconductors like Nb3Sn can drastically reduce the BCS part of the surface resistance. The temperature independent part of the surface resistance (residual resistance) can therefore become dominant, and has its own, different frequency dependence. We have developed a model to analyze cryogenic cooling power requirements for SRF cavities as function of operating frequency, temperature, and trapped flux to evaluate the impact of the novel low-loss SRF surfaces on the questions of optimal operating frequency and frequency limit. We show that high-frequency SRF cavities now become a realistic option for future SRF driven accelerators. As the transverse cavity size decreases inversely with respect to its resonant frequency, such high-frequency SRF cavities could greatly reduce cost.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB009

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

TUPB039

Electropolishing of Niobium from Deep Eutectic Solvents Based on Choline Chloride

ion, cavity, niobium, SRF

475

Q.W. Chu, H. Guo, Y. He, L. Li, P.R. Xiong, Z.M. You, S.H. Zhang
IMP/CAS, Lanzhou, People's Republic of China

Niobium (Nb) was successfully electropolished from a green ionic liquid, choline chloride/urea deep eutectic solvent (DES). This paper was to investigate the influence of various electropolishing parameters, including electropolishing time, temperature and voltage, on the electropolishing rate, surface roughness, glossiness and microstructure of Nb. The result showed that the electropolishing parameters had a significant impact on the performance of Nb. Based on surface analysis by scanning electron microscope (SEM) and atomic force microscope (AFM), smooth Nb can be achieved under properly controlled conditions.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB039

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

TUPB111

R&D Activities on Centrifugal Barrel Polishing of 1.3 GHz Niobium Cavities at DESY/University of Hamburg

ion, cavity, niobium, laser

655

A.L. Prudnikava, B. Foster, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
A. Ermakov, B. Foster
DESY, Hamburg, Germany
Y. Tamashevich
HZB, Berlin, Germany

In this paper the status of research activities at ILC-HiGrade Lab (DESY/University of Hamburg) on Centrifugal Barrel Polishing (CBP) of 1.3 GHz Niobium Cavities is presented. We focus on CBP based on the polishing recipe reported by Fermi National Laboratory and Jefferson Lab*. The aim is to gain a better understanding of the limitations of this technique, detailed characterization of the treated surface after each polishing step using a "coupon" single cell cavity. Plastic deformations upon initial CBP steps, embedded polishing media and residual damage upon final polishing were investigated at different areas of the cavity.
* C. A. Cooper, L. D. Cooley, Supercond. Sci. Technol. 26 (2013) 015011

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB111

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THPB019

Simulation of the Thermoelectrically Generated Magnetic Field in a SC Nine-cell Cavity

ion, cavity, simulation, experiment

771

J.M. Köszegi, J. Knobloch, O. Kugeler
HZB, Berlin, Germany

Several studies showed that thermocurrents generate a magnetic field in a horizontal cavity test assembly or cryomodul, which may get trapped during the superconducting phase transition. The trapped flux causes additional dissipation during operation and can therefore significantly degrade the cavity's quality factor. We simulated the distribution of the generated magnetic field for different temperature distributions and compared the results to experimental findings. Furthermore, the impact of a growing superconducting area was investigated. The simulations complement the experimental studies because measurements were only feasible with a limited number of probes and restricted to selected locations and orientations. The simulations allow to analyze this data in the context of the whole system.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB019

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THPB037

Cavity Fundamental Mode and Beam Interaction in CEPC Main Ring

ion, cavity, beam-loading, luminosity

825

D.J. Gong, J. Gao, D. Wang, J.Y. Zhai
IHEP, Beijing, People's Republic of China

Circular electron positron collider (CEPC) is design as a particle factory for Higgs, W and Z. The preliminary study is undertaken for CEPC cavity fundamental mode and beam interaction in this paper. The baseline of CEPC is DR scheme, the alternative is the APDR scheme. Beam loading effects and the corresponding longitudinal beam dynamics of both CEPC DR and APDR are elaborated in this article. The phase shift and voltage decrease are calculated by the analytic formula and the program. Furthermore, the longitudinal coupled-bunch instability is also studied. At last, the RF parameters are calculated for CEPC 100km APDR, in order to match the machine parameters and relieve the beam loading effects.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB037

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

THPB061

Effect Of Dislocations On the Thermal Conductivity Of Superconducting Nb

ion, scattering, electron, cavity

886

P. Xu, N.T. Wright
MSU, East Lansing, Michigan, USA
T.R. Bieler
Michigan State University, East Lansing, Michigan, USA

Funding: This work is funded by DOE and OHEP through grant number DE-FOA-0001438.
The thermal conductivity of Niobium (Nb) often experiences a local maximum (a phonon peak) at a temperature between 1.8 and 3 K. While the magnitude of the phonon peak has been shown to be related to the dislocation density and may be influenced by manufacturing processes, little has been discussed as to the temperature at which the peak occurs. In examining these phenomena, it has been determined that more explicit accounting of phonon–dislocation scattering in a popular model better represents the thermal conductivity at temperatures colder than 3 K. Scaled sensitivity coefficients show this term to have similar influence as the phonon-electron and phonon-boundary scattering terms. Results using the enhanced model also show an apparent threshold of dislocation density below which there is little contribution to the thermal conductivity of Nb.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB061

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