SRF2013 - List of Authors (Proslier, Th.)

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.

TUP079

ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy

631

A-M. Valente-Feliciano, G.V. Eremeev, H.L. Phillips, C.E. Reece
JLAB, Newport News, Virginia, USA
C. Cao
Illinois Institute of Technology, Chicago, IL, USA
Th. Proslier
ANL, Argonne, USA
J.K. Spradlin
JLab, Newport News, Virginia, USA
T. Tao
UIC, Chicago, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favorable template for growing the final surface exposed to SRF fields. The influence of the deposition energy for both hetero-epitaxial and fiber growth modes on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance.

TUP086

Cryogen-Free RF System Studies Using Cryocooler-Cooled Magnesium Diboride-Coated Copper RF Cavities

663

A. Nassiri, R. Kustom, Th. Proslier
ANL, Argonne, USA
T. Tan, X. Xi
TU, Philadelphia, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06H11357.
Studies on the application of magnesium diboride(MgB2)high-Tc superconducting films have shown promise for use with rf cavities. Studies are directed towards applying the films to niobium cavities with the goal to increase accelerating gradients to greater than 50 MeV/m. However, studies also have shown that MgB2 films, with a critical temperature over four times higher than Nb, have surface resistances equal, or nearly equal, at 8-12 K, to what is achieved with niobium at 4 K. It might be possible to design and operate cavity systems in the 8-12K temperature range with cryocoolers that are currently available. The current cryocoolers can remove as much as 20 watts per unit in the range of 8-12K. This suggests that helium-free superconducting RF systems are possible for future light sources and possible industrial and medical linear accelerators. Our current research is directed towards depositing MgB2 films onto copper, or other high thermal conductivity metal, substrates which would allow future cavities to be fabricated as film coated copper structures. We have started atomic layer deposition and Hybrid chemical vapor deposition studies of MgB2 on 2-inch copper coupons.

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.

TUP079	ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy	631
	A-M. Valente-Feliciano, G.V. Eremeev, H.L. Phillips, C.E. Reece JLAB, Newport News, Virginia, USA C. Cao Illinois Institute of Technology, Chicago, IL, USA Th. Proslier ANL, Argonne, USA J.K. Spradlin JLab, Newport News, Virginia, USA T. Tao UIC, Chicago, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favorable template for growing the final surface exposed to SRF fields. The influence of the deposition energy for both hetero-epitaxial and fiber growth modes on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance.

TUP086	Cryogen-Free RF System Studies Using Cryocooler-Cooled Magnesium Diboride-Coated Copper RF Cavities	663
	A. Nassiri, R. Kustom, Th. Proslier ANL, Argonne, USA T. Tan, X. Xi TU, Philadelphia, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06H11357. Studies on the application of magnesium diboride(MgB2)high-Tc superconducting films have shown promise for use with rf cavities. Studies are directed towards applying the films to niobium cavities with the goal to increase accelerating gradients to greater than 50 MeV/m. However, studies also have shown that MgB2 films, with a critical temperature over four times higher than Nb, have surface resistances equal, or nearly equal, at 8-12 K, to what is achieved with niobium at 4 K. It might be possible to design and operate cavity systems in the 8-12K temperature range with cryocoolers that are currently available. The current cryocoolers can remove as much as 20 watts per unit in the range of 8-12K. This suggests that helium-free superconducting RF systems are possible for future light sources and possible industrial and medical linear accelerators. Our current research is directed towards depositing MgB2 films onto copper, or other high thermal conductivity metal, substrates which would allow future cavities to be fabricated as film coated copper structures. We have started atomic layer deposition and Hybrid chemical vapor deposition studies of MgB2 on 2-inch copper coupons.

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]