SRF2017 - List of Authors (Grassellino, A.)

Paper

Title

Page

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

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]

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

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TUYAA03

Electron Mean Free Path Dependence of the Vortex Surface Impedance

M. Checchin, A. Grassellino, M. Martinello, A. Romanenko
Fermilab, Batavia, Illinois, USA

In the present study the radio-frequency complex response of trapped vortices in superconductors is calculated. The motion equation for a magnetic flux line is solved assuming a bi-dimensional and mean-free-path-dependent Lorentzian-shaped pinning potential. The resulting surface resistance shows the unprecedented bell-shaped trend as a function of the mean-free-path observed in our previous experimental work. We demonstrate that such bell-shaped trend of the surface resistance, as a function of the mean-free-path, may be described as the interplay of the two limiting regimes of the surface resistance, for low and large mean-free-path values: pinning and flux-flow regimes respectively. By tackling the frequency dependence of the surface resistance, we also demonstrate that the separation between pinning- and flux-flow-dominated regimes cannot be determined only by the depinning frequency. The dissipation regime can be indeed tuned either by acting on the frequency or on the mean-free-path value.

Slides TUYAA03 [6.144 MB]

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TUPB071

Test Result of 650 MHz, Beta 0.61 Single-cell Niobium Cavity

553

S. Seth, P. Bhattacharyya, A. Dutta Gupta, S. Ghosh, S. Ghosh, A. Mandal, S. Som
VECC, Kolkata, India
A. Grassellino, T.N. Khabiboulline, O.S. Melnychuk, C.S. Mishra, T.H. Nicol, A.M. Rowe, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA
M.P. Kelly, T. Reid
ANL, Argonne, Illinois, USA
K.K. Mistri, P.N. Prakash
IUAC, New Delhi, India

VECC has been involved in the design, analysis and development of 650 MHz, beta 0.61 (LB650), elliptical Superconducting RF linac cavity, as part of research and development activities on SRF cavities and associated technologies under Indian Institutions Fermilab Collaboration (IIFC). A single-cell niobium cavity has been indigenously designed and developed at VECC, with the help of Electron Beam Welding (EBW) facility at IUAC, New Delhi. Various measurements, processing and testing at 2K in Vertical Test Stand (VTS) of the single-cell cavity was carried out at ANL and Fermilab, USA, with active participation of VECC engineers. It achieved a maximum accelerating gradient(Eacc) of 34.5 MV/m with Quality Factor of 2·10⁹ and 30 MV/m with Quality Factor of 1.5·10¹⁰. This is probably the highest accelerating gradient achieved so far in the world for LB650 cavities. This paper describes the design, fabrication and measurement of the single cell niobium cavity. Cavity processing and test results of Vertical Test of the single-cell niobium cavity are also presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB071

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FRXAA03

Performance of the High Q CW Prototype Cryomodule for LCLS-II at FNAL

G. Wu, A. Grassellino, E.R. Harms, N. Solyak
Fermilab, Batavia, Illinois, USA

Funding: Work is supported under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
Continuous wave (CW) operation of LCLS-II cryomodules require substantial design changes to previously designed 1.3 GHz ILC type cryomodule. The new design uses innovative nitrogen doped cavities together with a helium vessel that provides high thermal gradient on the cavities during a fast cool down. Magnetic shielding uses two layers outside of helium vessel and a single layer that completely encapsulates the end groups except the beam apertures. Sophisticated magnetic hygiene includes vacuum vessel demagnetization, magnetic screening of the components and final demagnetization to the assembled cryomodule. Fermilab successfully assembled a preproduction LCLS-II cryomodule that achieved unprecedented cavity quality factors of 3.0·10¹⁰ at a nominal cryomodule voltage. The ambient fields in the cavities were near zero. This article describes historic cavity performance under various cool down parameters. Cavity performance retained very well compared to that of vertical tests.

Slides FRXAA03 [3.700 MB]

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Paper	Title	Page
TUYAA02	Advancement in the Understanding of the Field and Frequency Dependent Microwave Surface Resistance of Niobium	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
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUYAA03	Electron Mean Free Path Dependence of the Vortex Surface Impedance
	M. Checchin, A. Grassellino, M. Martinello, A. Romanenko Fermilab, Batavia, Illinois, USA
	In the present study the radio-frequency complex response of trapped vortices in superconductors is calculated. The motion equation for a magnetic flux line is solved assuming a bi-dimensional and mean-free-path-dependent Lorentzian-shaped pinning potential. The resulting surface resistance shows the unprecedented bell-shaped trend as a function of the mean-free-path observed in our previous experimental work. We demonstrate that such bell-shaped trend of the surface resistance, as a function of the mean-free-path, may be described as the interplay of the two limiting regimes of the surface resistance, for low and large mean-free-path values: pinning and flux-flow regimes respectively. By tackling the frequency dependence of the surface resistance, we also demonstrate that the separation between pinning- and flux-flow-dominated regimes cannot be determined only by the depinning frequency. The dissipation regime can be indeed tuned either by acting on the frequency or on the mean-free-path value.
	Slides TUYAA03 [6.144 MB]
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPB071	Test Result of 650 MHz, Beta 0.61 Single-cell Niobium Cavity	553
	S. Seth, P. Bhattacharyya, A. Dutta Gupta, S. Ghosh, S. Ghosh, A. Mandal, S. Som VECC, Kolkata, India A. Grassellino, T.N. Khabiboulline, O.S. Melnychuk, C.S. Mishra, T.H. Nicol, A.M. Rowe, D.A. Sergatskov Fermilab, Batavia, Illinois, USA M.P. Kelly, T. Reid ANL, Argonne, Illinois, USA K.K. Mistri, P.N. Prakash IUAC, New Delhi, India
	VECC has been involved in the design, analysis and development of 650 MHz, beta 0.61 (LB650), elliptical Superconducting RF linac cavity, as part of research and development activities on SRF cavities and associated technologies under Indian Institutions Fermilab Collaboration (IIFC). A single-cell niobium cavity has been indigenously designed and developed at VECC, with the help of Electron Beam Welding (EBW) facility at IUAC, New Delhi. Various measurements, processing and testing at 2K in Vertical Test Stand (VTS) of the single-cell cavity was carried out at ANL and Fermilab, USA, with active participation of VECC engineers. It achieved a maximum accelerating gradient(Eacc) of 34.5 MV/m with Quality Factor of 2·10⁹ and 30 MV/m with Quality Factor of 1.5·10¹⁰. This is probably the highest accelerating gradient achieved so far in the world for LB650 cavities. This paper describes the design, fabrication and measurement of the single cell niobium cavity. Cavity processing and test results of Vertical Test of the single-cell niobium cavity are also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB071
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FRXAA03	Performance of the High Q CW Prototype Cryomodule for LCLS-II at FNAL
	G. Wu, A. Grassellino, E.R. Harms, N. Solyak Fermilab, Batavia, Illinois, USA
	Funding: Work is supported under Contract No. De-AC02-07CH11359 with the United States Department of Energy. Continuous wave (CW) operation of LCLS-II cryomodules require substantial design changes to previously designed 1.3 GHz ILC type cryomodule. The new design uses innovative nitrogen doped cavities together with a helium vessel that provides high thermal gradient on the cavities during a fast cool down. Magnetic shielding uses two layers outside of helium vessel and a single layer that completely encapsulates the end groups except the beam apertures. Sophisticated magnetic hygiene includes vacuum vessel demagnetization, magnetic screening of the components and final demagnetization to the assembled cryomodule. Fermilab successfully assembled a preproduction LCLS-II cryomodule that achieved unprecedented cavity quality factors of 3.0·10¹⁰ at a nominal cryomodule voltage. The ambient fields in the cavities were near zero. This article describes historic cavity performance under various cool down parameters. Cavity performance retained very well compared to that of vertical tests.
	Slides FRXAA03 [3.700 MB]
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)