SRF2013 - List of Authors (Zasadzinski, J.)

Paper

Title

Page

Probing Hot Spot and Cold Spot of SRF Cavities with Tunneling and Raman Spectroscopies

466

C. Cao
Illinois Institute of Technology, Chicago, IL, USA
G. Ciovati
JLAB, Newport News, Virginia, USA
L.D. Cooley, A. Grassellino
Fermilab, Batavia, USA
N. Groll, Th. Proslier
ANL, Argonne, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

Point contact tunneling and Raman spectroscopies are presented on high purity Nb samples, including pieces from hot and col spot regions of tested SRF cavities and Nb coupons subject to similar treatment. High quality tunneling spectra were observed on cold spots, revealing the bulk Nb gap, indicating minimal surface contamination. Hot spots exhibit high smearing suggestive of pair breaking along with generally lower superconducting gap. In addition, pronounced zero bias conductance peaks were frequently observed indicative of spin-flip tunneling and thus magnetic impurities in the oxide layer. Optical microscopy reveals higher density of surface blemishes on hot spots. Raman spectra inside those blemishes show clear difference from surrounding areas, exhibiting enhanced intensity peaks identified as either amorphous carbon, hydrocarbons or the ordered NbC phase. The presence of surface NbC is consistent with TEM studies, and these inclusions exhibit enhanced second order phonon response. Such regions with high concentrations of impurities are expected to suppress the local superconductivity and may explain the formation of hot spots.

TUP043

Nanostructural TEM/STEM Studies of Hot and Cold Spots in SRF Cavities

504

Y. Trenikhina, J. Zasadzinski
IIT, Chicago, Illinois, USA
A. Romanenko
Fermilab, Batavia, USA

Direct TEM/STEM imaging and spectroscopic chemical characterization by EELS/EDS of the surface of the SRF cavity cutouts before and after the treatments (e.g. in situ mild vacuum bake and rinsing with hydrofluoric acid) down to subnanometer scale is implemented to correspond the changes in niobium surface to the SRF performance of the cavities. We also report current results of the direct search, using cryogenic TEM stage, for suggested phase transformations in the niobium-hydrogen system* on “hot” and “cold” spot cavity cutouts, which may help clarifying the mechanism of the high field Q slope and its empirical cure.
*A. Romanenko, F. Barkov, L. D. Cooley, A. Grassellino, Supercond. Sci. Technol. 26 (2013) 035003.

WEIOC03

Atomic Layer Deposition of Thin Superconducting Films and Multilayers: Coupons and Cavity Tests

Th. Proslier, N. Groll, J. Klug, M.J. Pellin
ANL, Argonne, USA
G. Ciovati, P. Kneisel, A-M. Valente-Feliciano
JLAB, Newport News, Virginia, USA
A. Grassellino, A. Romanenko
Fermilab, Batavia, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

Funding: DOE-office of Science, High Energy Physics.
I will present a summary of the work done over the last 2 years that encompasses both coupons study of thin superconducting films and multilayers and preliminary superconducting RF cavity tests coated by ALD. I will also present results of Nb onto Copper.

Slides WEIOC03 [25.554 MB]

Paper	Title	Page
TUP019	Probing Hot Spot and Cold Spot of SRF Cavities with Tunneling and Raman Spectroscopies	466
	C. Cao Illinois Institute of Technology, Chicago, IL, USA G. Ciovati JLAB, Newport News, Virginia, USA L.D. Cooley, A. Grassellino Fermilab, Batavia, USA N. Groll, Th. Proslier ANL, Argonne, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Point contact tunneling and Raman spectroscopies are presented on high purity Nb samples, including pieces from hot and col spot regions of tested SRF cavities and Nb coupons subject to similar treatment. High quality tunneling spectra were observed on cold spots, revealing the bulk Nb gap, indicating minimal surface contamination. Hot spots exhibit high smearing suggestive of pair breaking along with generally lower superconducting gap. In addition, pronounced zero bias conductance peaks were frequently observed indicative of spin-flip tunneling and thus magnetic impurities in the oxide layer. Optical microscopy reveals higher density of surface blemishes on hot spots. Raman spectra inside those blemishes show clear difference from surrounding areas, exhibiting enhanced intensity peaks identified as either amorphous carbon, hydrocarbons or the ordered NbC phase. The presence of surface NbC is consistent with TEM studies, and these inclusions exhibit enhanced second order phonon response. Such regions with high concentrations of impurities are expected to suppress the local superconductivity and may explain the formation of hot spots.

TUP043	Nanostructural TEM/STEM Studies of Hot and Cold Spots in SRF Cavities	504
	Y. Trenikhina, J. Zasadzinski IIT, Chicago, Illinois, USA A. Romanenko Fermilab, Batavia, USA
	Direct TEM/STEM imaging and spectroscopic chemical characterization by EELS/EDS of the surface of the SRF cavity cutouts before and after the treatments (e.g. in situ mild vacuum bake and rinsing with hydrofluoric acid) down to subnanometer scale is implemented to correspond the changes in niobium surface to the SRF performance of the cavities. We also report current results of the direct search, using cryogenic TEM stage, for suggested phase transformations in the niobium-hydrogen system* on “hot” and “cold” spot cavity cutouts, which may help clarifying the mechanism of the high field Q slope and its empirical cure. *A. Romanenko, F. Barkov, L. D. Cooley, A. Grassellino, Supercond. Sci. Technol. 26 (2013) 035003.

WEIOC03	Atomic Layer Deposition of Thin Superconducting Films and Multilayers: Coupons and Cavity Tests
	Th. Proslier, N. Groll, J. Klug, M.J. Pellin ANL, Argonne, USA G. Ciovati, P. Kneisel, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA A. Grassellino, A. Romanenko Fermilab, Batavia, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: DOE-office of Science, High Energy Physics. I will present a summary of the work done over the last 2 years that encompasses both coupons study of thin superconducting films and multilayers and preliminary superconducting RF cavity tests coated by ALD. I will also present results of Nb onto Copper.
	Slides WEIOC03 [25.554 MB]