SRF2013 - List of Authors (Chandrasekaran, S.K.)

Paper	Title	Page
MOP013	SRF Developments at MSU for FRIB	106
	K. Saito, N.K. Bultman, F. Casagrande, S. Chouhan, C. Compton, K. Elliott, A. Facco, M.J. Johnson, S. Jones, M. Leitner, S.J. Miller, R. Oweiss, J.P. Ozelis, J. Popielarski, L. Popielarski, S. Shanab, J. Wei, T. Xu, Y. Yamazaki, Y. Zhang, Z. Zheng FRIB, East Lansing, Michigan, USA S.K. Chandrasekaran MSU, East Lansing, USA K. Hosoyama KEK, Ibaraki, Japan
	FRIB has built up a new SRF development group for future SRF research and development at MSU. This paper will report on the present status of development for fundamental couplers, pneumatic tuners for HWR, magnetic shielding and superconducting solenoids, barrel polishing techniques for HWR, a cavity steam cleaning method, and niobium material characterization efforts.

MOP033	Quality Assurance and Acceptance Testing of Niobium Material for Use in the Construction of the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU)	174
	C. Compton, D. Miller FRIB, East Lansing, Michigan, USA T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA S.K. Chandrasekaran, N.T. Wright MSU, East Lansing, USA
	Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University Niobium is the current material of choice for the fabrication of superconducting radio frequency (SRF) cavities used in SRF based accelerators. Although niobium specifications for this application have been well established, material properties of as-received materials can still vary substantially. As required for the FRIB accelerator, large volumes (60,000 lbs) of niobium materials (sheet, tube, and flange) have been contracted to several niobium vendors. The FRIB cavity designs require very large niobium sheets, increasing the difficulty in fabrication and potential for contamination. FRIB has developed and initiated plans to control niobium specifications and perform incoming acceptance checks to ensure quality is maintained. Acceptance results from the first niobium shipment will be presented, looking at several production lots from the same vendor and across multiple vendors. Non-conforming results were observed and will be discussed including follow-up investigations and mitigation strategies to improve quality of future shipments.

TUP067	Hydrogen Saturation and the Thermal Conductivity of Superconducting Niobium	589
	S.K. Chandrasekaran MSU, East Lansing, USA T.R. Bieler Michigan State University, East Lansing, USA C. Compton FRIB, East Lansing, USA N.T. Wright (MSU), East Lansing, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222 The thermal conductivity k of Nb at less than 3 K is dominated by phonon transport. In Nb with sufficiently few lattice imperfections, a maximum in k occurs at 1.8 K, called the phonon peak (PP). A large PP is desired to reduce potential local hot spots and contributes to an increased Q factor. The magnitude of the PP is sensitive to SRF cavity manufacturing processes. The effect of interstitial hydrogen on the magnitude of the PP is examined by subjecting two bicrystal Nb specimens to 300 C for 1 h in a 75% H2, 25% N2 atmosphere at 0.5 atm. Prior to hydrogen infusion, specimen 1 was heated to 800 C for 2 h, while specimen 2 was heated to 1100 C for 4 h. Both specimens displayed a 25% reduction in the PP due to the additional hydrogen, independent of their crystal orientations and heat treatment histories. An 800 C vacuum heating for 2 h was found to be sufficient to recover the PP in specimen 1, while an 1100 C heating for 4 h was required to recover the PP in one of the grains of specimen 2. The results suggest that hydrogen trapped in the Nb lattice will degas when the Nb is heated to at least the temperature to which it was heated at prior to the hydrogen infusion step.

THP046	Magnetic Material Characterization & SC Solenoid Coil Package Design for FRIB	1009
	K. Saito, S. Chouhan, C. Compton, J. DeKamp, M. Leitner, F. Marti, J.P. Ozelis, S. Shanab, G.J. Velianoff, X. Wu, Y. Yamazaki, A. Zeller, Y. Zhang, Q. Zhao FRIB, East Lansing, Michigan, USA S.K. Chandrasekaran MSU, East Lansing, USA K. Hosoyama KEK, Ibaraki, Japan
	To date SRF technology is extending to large scale heavy ion LINACs, where SRF cavities accelerate beams from very low energy to high energy. In this application, superconducting (SC) solenoids are installed inside the cryomodule to provide strong beam focusing with enhanced space efficiency. FRIB will use local magnetic shielding, where magnetic shielding by Cryoperm or A4K is located close to the cavity at 2K. In this scheme rather strong magnetic fringe fields from the SC solenoid expose the shielding material and will magnetize it. An efficient degaussing process is required as cure against such magnetization. Magnetic material characterization of magnetic shielding materials is very important to be able to plan effective degaussing procedures. The paper will also discuss the design of FRIB solenoids optimized for cost, reliability, and robust long-term operation. NbTi wire performance criteria are discussed in addition to solenoid operational margins.

Paper

Title

Page

SRF Developments at MSU for FRIB

106

K. Saito, N.K. Bultman, F. Casagrande, S. Chouhan, C. Compton, K. Elliott, A. Facco, M.J. Johnson, S. Jones, M. Leitner, S.J. Miller, R. Oweiss, J.P. Ozelis, J. Popielarski, L. Popielarski, S. Shanab, J. Wei, T. Xu, Y. Yamazaki, Y. Zhang, Z. Zheng
FRIB, East Lansing, Michigan, USA
S.K. Chandrasekaran
MSU, East Lansing, USA
K. Hosoyama
KEK, Ibaraki, Japan

FRIB has built up a new SRF development group for future SRF research and development at MSU. This paper will report on the present status of development for fundamental couplers, pneumatic tuners for HWR, magnetic shielding and superconducting solenoids, barrel polishing techniques for HWR, a cavity steam cleaning method, and niobium material characterization efforts.

MOP033

Quality Assurance and Acceptance Testing of Niobium Material for Use in the Construction of the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU)

174

C. Compton, D. Miller
FRIB, East Lansing, Michigan, USA
T.R. Bieler, D. Kang
Michigan State University, East Lansing, Michigan, USA
S.K. Chandrasekaran, N.T. Wright
MSU, East Lansing, USA

Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University
Niobium is the current material of choice for the fabrication of superconducting radio frequency (SRF) cavities used in SRF based accelerators. Although niobium specifications for this application have been well established, material properties of as-received materials can still vary substantially. As required for the FRIB accelerator, large volumes (60,000 lbs) of niobium materials (sheet, tube, and flange) have been contracted to several niobium vendors. The FRIB cavity designs require very large niobium sheets, increasing the difficulty in fabrication and potential for contamination. FRIB has developed and initiated plans to control niobium specifications and perform incoming acceptance checks to ensure quality is maintained. Acceptance results from the first niobium shipment will be presented, looking at several production lots from the same vendor and across multiple vendors. Non-conforming results were observed and will be discussed including follow-up investigations and mitigation strategies to improve quality of future shipments.

TUP067

Hydrogen Saturation and the Thermal Conductivity of Superconducting Niobium

589

S.K. Chandrasekaran
MSU, East Lansing, USA
T.R. Bieler
Michigan State University, East Lansing, USA
C. Compton
FRIB, East Lansing, USA
N.T. Wright
(MSU), East Lansing, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222
The thermal conductivity k of Nb at less than 3 K is dominated by phonon transport. In Nb with sufficiently few lattice imperfections, a maximum in k occurs at 1.8 K, called the phonon peak (PP). A large PP is desired to reduce potential local hot spots and contributes to an increased Q factor. The magnitude of the PP is sensitive to SRF cavity manufacturing processes. The effect of interstitial hydrogen on the magnitude of the PP is examined by subjecting two bicrystal Nb specimens to 300 C for 1 h in a 75% H2, 25% N2 atmosphere at 0.5 atm. Prior to hydrogen infusion, specimen 1 was heated to 800 C for 2 h, while specimen 2 was heated to 1100 C for 4 h. Both specimens displayed a 25% reduction in the PP due to the additional hydrogen, independent of their crystal orientations and heat treatment histories. An 800 C vacuum heating for 2 h was found to be sufficient to recover the PP in specimen 1, while an 1100 C heating for 4 h was required to recover the PP in one of the grains of specimen 2. The results suggest that hydrogen trapped in the Nb lattice will degas when the Nb is heated to at least the temperature to which it was heated at prior to the hydrogen infusion step.

THP046

Magnetic Material Characterization & SC Solenoid Coil Package Design for FRIB

1009

K. Saito, S. Chouhan, C. Compton, J. DeKamp, M. Leitner, F. Marti, J.P. Ozelis, S. Shanab, G.J. Velianoff, X. Wu, Y. Yamazaki, A. Zeller, Y. Zhang, Q. Zhao
FRIB, East Lansing, Michigan, USA
S.K. Chandrasekaran
MSU, East Lansing, USA
K. Hosoyama
KEK, Ibaraki, Japan

To date SRF technology is extending to large scale heavy ion LINACs, where SRF cavities accelerate beams from very low energy to high energy. In this application, superconducting (SC) solenoids are installed inside the cryomodule to provide strong beam focusing with enhanced space efficiency. FRIB will use local magnetic shielding, where magnetic shielding by Cryoperm or A4K is located close to the cavity at 2K. In this scheme rather strong magnetic fringe fields from the SC solenoid expose the shielding material and will magnetize it. An efficient degaussing process is required as cure against such magnetization. Magnetic material characterization of magnetic shielding materials is very important to be able to plan effective degaussing procedures. The paper will also discuss the design of FRIB solenoids optimized for cost, reliability, and robust long-term operation. NbTi wire performance criteria are discussed in addition to solenoid operational margins.