SRF2013 - List of Authors (Groll, N.)

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.

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.

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]