IPAC2018 - List of Authors (Romanenko, A.S.)

Paper	Title	Page
WEYGBF2	Pathway to High Gradients in Superconducting rf Cavities by Avoiding Flux Dissipation
	A.S. Romanenko Fermilab, Batavia, Illinois, USA
	Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. It is currently believed in the field of SRF that the limit of the achievable accelerating gradients is set by the DC superheating field value, which guides most of the theoretical and experimental studies in this direction. However, it was recently proposed* that another mechanism is currently enabling both the existing SRF cavities with the quench field in excess of niobium Hc1, and providing the path forward to higher gradients, namely the vortex nucleation time slower than the rf period. If true, differently from currently pursued higher DC Hsh materials (e.g. Nb3Sn, MgB2 etc) or multi-layered structures, the new proposed directions are doping of the top niobium surface with special types of inelastic electron-phonon scattering "slowing down" impurities, or coating with thin layers of LOW (and not high) Tc superconductors. Both experimental and theoretical progress at Fermilab in this new area will be presented. *A. Romanenko, TTC Topical Workshop - RF Superconductivity: Pushing Cavity Performance Limits, Fermilab, Batavia, IL, 2017, https://indico.fnal.gov/event/15177/session/3/contribution/27
	Slides WEYGBF2 [3.780 MB]
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WEPMK016	New Insight on Nitrogen Infusion Revealed by Successive Nanometric Material Removal	2665
	M. Checchin, A. Grassellino, M. Martinello, O.S. Melnychuk, S. Posen, A.S. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	In this study we present new insight on low temperature nitrogen infusion on bulk niobium superconducting radio-frequency (SRF) cavities. Nitrogen infusion is a thermal treatment recently discovered at Fermilab that allows to reach high accelerating gradients, of the order of 45MV/m, with high Q-factors, of the order of 2 · 10¹⁰. Detailed depth dependent RF studies (by means of subsequent HF rinses) and comparisonwith SIMS results pinpointed interstitial nitrogen as the responsible for the improved performance and uncovered the extension of its profile inside the material.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK016
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WEPML013	Anti-Q-slope enhancement in high-frequency niobium cavities	2707
	M. Martinello, S. Aderhold, S.K. Chandrasekaran, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A.S. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	N-doped 1.3 GHz niobium cavities showed for the first time the so-called anti-Q-slope, i.e. the increasing of the Q-factor as a function of the accelerating field. It was verified that the anti-Q-slope is consequence of the decreasing of the temperature-dependent component of the surface resistance as a function of the field. This trend is opposite compared to the increasing of the surface resistance previously observed in 1.3 GHz standard (EP, BCP, 120 C baked) niobium cavities. The effect of the different state-of-the-art surface treatments on the field dependence of the surface resistance is studied for 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 Ghz cavities. This proceeding shows that the field dependence of the temperature-dependent component of the surface resistance has a strong frequency dependence and that the anti-Q-slope may appear even in clean niobium cavities if the resonant frequency is high enough, suggesting new routes toward the understanding of the anti-Q-slope effect.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML013
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Paper

Title

Page

WEYGBF2

Pathway to High Gradients in Superconducting rf Cavities by Avoiding Flux Dissipation

A.S. Romanenko
Fermilab, Batavia, Illinois, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
It is currently believed in the field of SRF that the limit of the achievable accelerating gradients is set by the DC superheating field value, which guides most of the theoretical and experimental studies in this direction. However, it was recently proposed* that another mechanism is currently enabling both the existing SRF cavities with the quench field in excess of niobium Hc1, and providing the path forward to higher gradients, namely the vortex nucleation time slower than the rf period. If true, differently from currently pursued higher DC Hsh materials (e.g. Nb3Sn, MgB2 etc) or multi-layered structures, the new proposed directions are doping of the top niobium surface with special types of inelastic electron-phonon scattering "slowing down" impurities, or coating with thin layers of LOW (and not high) Tc superconductors. Both experimental and theoretical progress at Fermilab in this new area will be presented.
*A. Romanenko, TTC Topical Workshop - RF Superconductivity: Pushing Cavity Performance Limits, Fermilab, Batavia, IL, 2017, https://indico.fnal.gov/event/15177/session/3/contribution/27

Slides WEYGBF2 [3.780 MB]

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WEPMK016

New Insight on Nitrogen Infusion Revealed by Successive Nanometric Material Removal

2665

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

In this study we present new insight on low temperature nitrogen infusion on bulk niobium superconducting radio-frequency (SRF) cavities. Nitrogen infusion is a thermal treatment recently discovered at Fermilab that allows to reach high accelerating gradients, of the order of 45MV/m, with high Q-factors, of the order of 2 · 10¹⁰. Detailed depth dependent RF studies (by means of subsequent HF rinses) and comparisonwith SIMS results pinpointed interstitial nitrogen as the responsible for the improved performance and uncovered the extension of its profile inside the material.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK016

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WEPML013

Anti-Q-slope enhancement in high-frequency niobium cavities

2707

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

N-doped 1.3 GHz niobium cavities showed for the first time the so-called anti-Q-slope, i.e. the increasing of the Q-factor as a function of the accelerating field. It was verified that the anti-Q-slope is consequence of the decreasing of the temperature-dependent component of the surface resistance as a function of the field. This trend is opposite compared to the increasing of the surface resistance previously observed in 1.3 GHz standard (EP, BCP, 120 C baked) niobium cavities. The effect of the different state-of-the-art surface treatments on the field dependence of the surface resistance is studied for 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 Ghz cavities. This proceeding shows that the field dependence of the temperature-dependent component of the surface resistance has a strong frequency dependence and that the anti-Q-slope may appear even in clean niobium cavities if the resonant frequency is high enough, suggesting new routes toward the understanding of the anti-Q-slope effect.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML013

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