SRF2021 - List of Authors (Grassellino, A.)

Paper	Title	Page
MOPFDV009	On the Nature of Surface Defects Found in 2/0 N-Doped 9-Cell Cavities	336
	A. Cano, D. Bafia, A. Grassellino, J. Lee, M. Martinello, A.S. Romanenko, T. Spina, Z-H. Sung Fermilab, Batavia, Illinois, USA
	In this contribution, we present a systematic study on the microstructure of 1.3 GHz 9-cell TESLA type SRF cavity, processed with 2/0 Nitrogen-doping surface treatment, to explain the premature quench phenomena commonly observed in N-doping treated cavities. The microstructure characterization was carried out using Secondary electron images, advanced metallurgical techniques such as EBSD in parallel with chemical information obtained from spectroscopic techniques. The most remarkable difference is observed in the ends-cavities (1 and 9), which showed roughening of the surface, revealing a series of morphologies associated with Nb cubic phase. The cell-to-cell analysis also showed standard features such as pits with different geometry and distribution, located in grains and grain boundaries. The defects found in this system suggest that the standard electropolishing chemical etching was insufficient to eliminate history defects produced during the manufacture of the cavity, without discarding the role of the impurities, N and O, that could have induced the growth of these morphologies. H. Padamsee, RF superconductivity (Wiley-VCH Verlag GmbH and Co., KGaA, Weinheim, 2009)
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPFDV009
About •	Received ※ 29 June 2021 — Revised ※ 11 March 2022 — Accepted ※ 10 May 2022 — Issue date ※ 11 May 2022
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MOPFDV010	Microstructure Changes Observed in the Near-Surface Region of SRF Nb Cavities Cutouts upon Cooling/Heating Cycles Using GI-Synchrotron XRD	339
	A. Cano, D. Bafia, A. Grassellino, J. Lee, M. Martinello, A.S. Romanenko, T. Spina, Z-H. Sung Fermilab, Batavia, Illinois, USA E.A. Karapetrova ANL, Lemont, Illinois, USA
	We have mapped microstructural changes in the near-surface region of Nb from SRF cavity-cutouts upon thermal cycles in the range from 300 to 30 K using grazing incidence synchrotron X-Ray diffraction (GIXRD). Segregation of secondary phases was observed after the thermal cycle, and their nature has been clarified and discussed in view of previous studies on hydrides formation in SRF bulk Nb cavities. The temperature dependence of the relative population of these formed phases was obtained from GIXRD patterns profile fitting. Both, Nb bulk matrix and the new phases formed after cool-down show specific structural features as thermal contraction/expansion, structural transitions, and Nb lattice variation due to the induced strain by precipitates formation. The information derived from this structural study can explain some phenomena as the dissipation at high accelerating field (i.e. High Field Q Slope, HFQS) in the Nb SRF performance as well as new mechanisms never addressed in previous studies. A Romanenko, F Barkov, LD Cooley, A Grassellino, Proximity breakdown of hydrides in superconducting niobium cavities, Superconductor Science and Technology, 2013
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPFDV010
About •	Received ※ 28 June 2021 — Revised ※ 12 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 23 September 2021
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THPTEV016	The Role of Oxygen Concentration in Enabling High Gradients in Niobium SRF Cavities	871
	D. Bafia, A. Grassellino, A.S. Romanenko Fermilab, Batavia, Illinois, USA
	We studied the role of O concentration with depth in the performance of Nb SRF cavities. An ensemble of electropolished 1.3 GHz cavities, which initially showed high field Q-slope (HFQS), was subjected to sequential testing and treatment with in-situ low temperature baking at various temperatures. We find that increasing the bake duration causes (i) an increase in the onset of HFQS until it is absent up to quench (ii) a non-monotonic relationship with the quench field (iii) an evolution of the RBCS toward a non-equilibrium behavior that drives anti-Q slope. Our data is qualitatively explained by assuming an O diffusion model and suggests that the mitigation of HFQS that arises from 120°C in-situ LTB is mediated by the diffusion of O from the native oxide which prevents the precipitation of proximity-coupled Nb nano-hydrides, in turn enabling higher quench fields. The decrease in quench field for cavities in which O has been diffused >90 nm from the RF surface may be due to a reduction of the field limit in the SS bilayer structure. We also suggest that the evolution of the RBCS occurs due to the absence of proximity coupled inclusions, bringing about non-equilibrium effects.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-THPTEV016
About •	Received ※ 22 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 13 October 2021 — Issue date ※ 23 November 2021
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FROFDV03	Investigating the Anomalous Frequency Variations Near Tc of Nb SRF Cavities	885
	D. Bafia, M. Checchin, A. Grassellino, A.S. Romanenko Fermilab, Batavia, Illinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	We report recent studies on the anomalous frequency variations of 1.3 GHz Nb SRF cavities near the transition temperature Tc and use them to investigate the underlying physics of state-of-the-art surface treatments. One such feature, a dip in frequency, correlates directly with the quality factor at 16 MV/m and the anti-Q slope that arise in cavities with dilute concentrations of N interstitial in the RF layer achieved via N-doping and mid temperature baking. For N interstitial, we find that the dip magnitude and Tc follow exponential relationships with the electronic mean free path. We present the first observation of the frequency dip near Tc in a cavity baked at 200 C in-situ for 11 hours, which is concurrent with the anti-Q slope, and may be driven by oxygen diffused from the native oxide, thus suggesting the possibility of ‘‘O-doping.’’ We also investigate the conductivities of two cavities that display different resonant frequency behaviors near Tc and suggest that the anti-Q slope and frequency dip phenomena may occur in the presence of interstitial N or possibly O that inhibit the formation of proximity coupled Nb nano-hydrides.
	Slides FROFDV03 [0.835 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-FROFDV03
About •	Received ※ 25 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 18 December 2021 — Issue date ※ 28 April 2022
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FROFDV04	9MeV Electron Irradiation on Nb Samples and 1.3GHz SRF Cavity
	T. Spina, A. Grassellino, A.S. Romanenko Fermilab, Batavia, Illinois, USA
	To enhance bulk Nb RF cavity performances at high accelerating field it is important to prevent precipitates formation. Doping and heat treatments can mitigate such effect and the most accredited theory is based on the presence of proximity-coupled niobium hydrides []. Irradiation can induce vacancy-2H complexes [] and in this study, the effects of 9MeV electrons on Nb samples and cavity up to fluences of 1.8x1021e/m2 are investigated. The size and density changes of micro-hydrides before and after irradiation was measured by cryo-laser confocal microscopy and a new analytic technique based on computer vision has been used. A strong reduction in hydrides size was found after irradiation and the hydrides formation temperature was shifted to lower values suggesting a reduction in both the activation energy barrier and the critical radius. We conclude that electron irradiation can indeed prevent the formation of large hydrides in H-loaded Nb bulk sample. 1.3GHz Nb cavity has also been submitted to electron irradiation treatment in stationary mode and Q vs E curves and T-map measurements before and after irradiations recorded the changes induced by radiation on cavity performance. [] A. Romanenko et al., Supercond. Sci. Technol. 26 (2013) 035003 [**]J. CíÅ¾ek et al. PHYSICAL REVIEW B 79 (2009) 054108
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FROKNV01	Will SRF Technology Revolutionize Quantum Computing?
	A. Grassellino Fermilab, Batavia, Illinois, USA
	Fermilab has been recently awarded a $115M National Quantum Center (Superconducting Quantum Materials and Systems Center, SQMS) for producing dramatic advancements in quantum technologies for computing and sensing. The center encompasses 20 partner institutions from the US and Italy including national labs, academia and industry, and will have as a main goal to build the first quantum computer at Fermilab, which will be based on SRF technology. Thanks to the long coherence time of SRF cavities in the quantum regime, the quantum computer prototype may be far superior than any quantum processors so far existing and enable new type of caluclations and simulations. This talk will explain the importance that SRF will play in the international quantum arena, highlight the National Quantum Initiative effort and the new SQMS Center activities, and in particular focus on explaining how the first quantum computer based on the SRF technology will come to life.
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

On the Nature of Surface Defects Found in 2/0 N-Doped 9-Cell Cavities

336

A. Cano, D. Bafia, A. Grassellino, J. Lee, M. Martinello, A.S. Romanenko, T. Spina, Z-H. Sung
Fermilab, Batavia, Illinois, USA

In this contribution, we present a systematic study on the microstructure of 1.3 GHz 9-cell TESLA type SRF cavity, processed with 2/0 Nitrogen-doping surface treatment, to explain the premature quench phenomena commonly observed in N-doping treated cavities. The microstructure characterization was carried out using Secondary electron images, advanced metallurgical techniques such as EBSD in parallel with chemical information obtained from spectroscopic techniques. The most remarkable difference is observed in the ends-cavities (1 and 9), which showed roughening of the surface, revealing a series of morphologies associated with Nb cubic phase. The cell-to-cell analysis also showed standard features such as pits with different geometry and distribution, located in grains and grain boundaries. The defects found in this system suggest that the standard electropolishing chemical etching was insufficient to eliminate history defects produced during the manufacture of the cavity, without discarding the role of the impurities, N and O, that could have induced the growth of these morphologies.
H. Padamsee, RF superconductivity (Wiley-VCH Verlag GmbH and Co., KGaA, Weinheim, 2009)

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPFDV009

About •

Received ※ 29 June 2021 — Revised ※ 11 March 2022 — Accepted ※ 10 May 2022 — Issue date ※ 11 May 2022

Cite •

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

MOPFDV010

Microstructure Changes Observed in the Near-Surface Region of SRF Nb Cavities Cutouts upon Cooling/Heating Cycles Using GI-Synchrotron XRD

339

A. Cano, D. Bafia, A. Grassellino, J. Lee, M. Martinello, A.S. Romanenko, T. Spina, Z-H. Sung
Fermilab, Batavia, Illinois, USA
E.A. Karapetrova
ANL, Lemont, Illinois, USA

We have mapped microstructural changes in the near-surface region of Nb from SRF cavity-cutouts upon thermal cycles in the range from 300 to 30 K using grazing incidence synchrotron X-Ray diffraction (GIXRD). Segregation of secondary phases was observed after the thermal cycle, and their nature has been clarified and discussed in view of previous studies on hydrides formation in SRF bulk Nb cavities. The temperature dependence of the relative population of these formed phases was obtained from GIXRD patterns profile fitting. Both, Nb bulk matrix and the new phases formed after cool-down show specific structural features as thermal contraction/expansion, structural transitions, and Nb lattice variation due to the induced strain by precipitates formation. The information derived from this structural study can explain some phenomena as the dissipation at high accelerating field (i.e. High Field Q Slope, HFQS) in the Nb SRF performance as well as new mechanisms never addressed in previous studies.
A Romanenko, F Barkov, LD Cooley, A Grassellino, Proximity breakdown of hydrides in superconducting niobium cavities, Superconductor Science and Technology, 2013

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPFDV010

About •

Received ※ 28 June 2021 — Revised ※ 12 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 23 September 2021

Cite •

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

THPTEV016

The Role of Oxygen Concentration in Enabling High Gradients in Niobium SRF Cavities

871

D. Bafia, A. Grassellino, A.S. Romanenko
Fermilab, Batavia, Illinois, USA

We studied the role of O concentration with depth in the performance of Nb SRF cavities. An ensemble of electropolished 1.3 GHz cavities, which initially showed high field Q-slope (HFQS), was subjected to sequential testing and treatment with in-situ low temperature baking at various temperatures. We find that increasing the bake duration causes (i) an increase in the onset of HFQS until it is absent up to quench (ii) a non-monotonic relationship with the quench field (iii) an evolution of the RBCS toward a non-equilibrium behavior that drives anti-Q slope. Our data is qualitatively explained by assuming an O diffusion model and suggests that the mitigation of HFQS that arises from 120°C in-situ LTB is mediated by the diffusion of O from the native oxide which prevents the precipitation of proximity-coupled Nb nano-hydrides, in turn enabling higher quench fields. The decrease in quench field for cavities in which O has been diffused >90 nm from the RF surface may be due to a reduction of the field limit in the SS bilayer structure. We also suggest that the evolution of the RBCS occurs due to the absence of proximity coupled inclusions, bringing about non-equilibrium effects.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-THPTEV016

About •

Received ※ 22 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 13 October 2021 — Issue date ※ 23 November 2021

Cite •

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

FROFDV03

Investigating the Anomalous Frequency Variations Near Tc of Nb SRF Cavities

885

D. Bafia, M. Checchin, A. Grassellino, A.S. Romanenko
Fermilab, Batavia, Illinois, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

We report recent studies on the anomalous frequency variations of 1.3 GHz Nb SRF cavities near the transition temperature Tc and use them to investigate the underlying physics of state-of-the-art surface treatments. One such feature, a dip in frequency, correlates directly with the quality factor at 16 MV/m and the anti-Q slope that arise in cavities with dilute concentrations of N interstitial in the RF layer achieved via N-doping and mid temperature baking. For N interstitial, we find that the dip magnitude and Tc follow exponential relationships with the electronic mean free path. We present the first observation of the frequency dip near Tc in a cavity baked at 200 C in-situ for 11 hours, which is concurrent with the anti-Q slope, and may be driven by oxygen diffused from the native oxide, thus suggesting the possibility of ‘‘O-doping.’’ We also investigate the conductivities of two cavities that display different resonant frequency behaviors near Tc and suggest that the anti-Q slope and frequency dip phenomena may occur in the presence of interstitial N or possibly O that inhibit the formation of proximity coupled Nb nano-hydrides.

Slides FROFDV03 [0.835 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-FROFDV03

About •

Received ※ 25 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 18 December 2021 — Issue date ※ 28 April 2022

Cite •

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

FROFDV04

9MeV Electron Irradiation on Nb Samples and 1.3GHz SRF Cavity

T. Spina, A. Grassellino, A.S. Romanenko
Fermilab, Batavia, Illinois, USA

To enhance bulk Nb RF cavity performances at high accelerating field it is important to prevent precipitates formation. Doping and heat treatments can mitigate such effect and the most accredited theory is based on the presence of proximity-coupled niobium hydrides [*]. Irradiation can induce vacancy-2H complexes [**] and in this study, the effects of 9MeV electrons on Nb samples and cavity up to fluences of 1.8x1021e/m2 are investigated. The size and density changes of micro-hydrides before and after irradiation was measured by cryo-laser confocal microscopy and a new analytic technique based on computer vision has been used. A strong reduction in hydrides size was found after irradiation and the hydrides formation temperature was shifted to lower values suggesting a reduction in both the activation energy barrier and the critical radius. We conclude that electron irradiation can indeed prevent the formation of large hydrides in H-loaded Nb bulk sample. 1.3GHz Nb cavity has also been submitted to electron irradiation treatment in stationary mode and Q vs E curves and T-map measurements before and after irradiations recorded the changes induced by radiation on cavity performance.
[*] A. Romanenko et al., Supercond. Sci. Technol. 26 (2013) 035003
[**]J. CíÅ¾ek et al. PHYSICAL REVIEW B 79 (2009) 054108

Cite •

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

FROKNV01

Will SRF Technology Revolutionize Quantum Computing?

A. Grassellino
Fermilab, Batavia, Illinois, USA

Fermilab has been recently awarded a $115M National Quantum Center (Superconducting Quantum Materials and Systems Center, SQMS) for producing dramatic advancements in quantum technologies for computing and sensing. The center encompasses 20 partner institutions from the US and Italy including national labs, academia and industry, and will have as a main goal to build the first quantum computer at Fermilab, which will be based on SRF technology. Thanks to the long coherence time of SRF cavities in the quantum regime, the quantum computer prototype may be far superior than any quantum processors so far existing and enable new type of caluclations and simulations. This talk will explain the importance that SRF will play in the international quantum arena, highlight the National Quantum Initiative effort and the new SQMS Center activities, and in particular focus on explaining how the first quantum computer based on the SRF technology will come to life.

Cite •

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