SRF2015 - List of Authors (Tajima, T.)

Paper	Title	Page
TUBA06	Increase in Vortex Penetration Field on Nb Ellipsoid Coated With a MbB2 Thin Film	512
	T. Tan, M.A. Wolak, X. Xi Temple University, Philadelphia, USA L. Civale, T. Tajima LANL, Los Alamos, New Mexico, USA
	Funding: DOE Office of Science/High Energy Physics Since SRF2013, there has been a remarkable progress in terms of sample measurement. Instead of measuring a flat film that allows magnetic field on both sides of the film, which does not simulate the situation on a SRF cavity correctly, an ellipsoidal bulk Nb (rugby-ball shape with ~8 mm long axis) was coated with a MgB2 film and its vortex penetration field has been measured with a SQUID magnetometer and compared with uncoated samples. After a number of measurements, vortex penetration field has been consistent with maximum critical RF field, superheating field. Here, we show that 100 nm and 200 nm thick MgB2 coating increases the vortex penetration field by up to ~70 mT, e.g., 240 mT (200 nm MgB2 coated Nb) vs. 170 mT (uncoated Nb) at 2.8 K (lowest measurement temperature) with the trend of increasing as temperature goes down. This is consistent with recent theoretical development saying that the increase is possible even without an insulation layer, which makes the coating easier. In this talk, the thickness dependence of the rise and comparison with theory will be shown.
	Slides TUBA06 [2.088 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB053	Research on MgB2 at LANL for the Application to SRF Structures	700
	T. Tajima, L. Civale, R.K. Schulze LANL, Los Alamos, New Mexico, USA
	Funding: U.S. Department of Energy (DOE) Office of Science Office of Nuclear Physics Early Career Research Program This paper is focused on the development of MgB2 coating technique at LANL. Using boron film samples obtained at a large furnace system, we succeeded in obtaining superconducting MgB2 films (Tc of up to 37 K so far) by reacting them with Mg vapor. The major improvements were 1) confinement of the Mg vapor in a hot zone to mitigate the insufficient Mg pressure due to condensation on low temperature surfaces of the connected vacuum pipes and 2) reduction of cooldown time, i.e., ~13 minutes instead of ~1 day with the large system to prevent MgB2 from decomposing.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA2A02	High Gradient Testing of the Five-Cell Superconducting RF Module With a PBG Coupler Cell	948
	S. Arsenyev MIT/PSFC, Cambridge, Massachusetts, USA C.H. Boulware, T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima LANL, Los Alamos, New Mexico, USA
	Funding: DOE Office of Science/Office of High Energy Physics Superconducting radio-frequency (SRF) accelerating structures allow high-gradient operation in continuous-wave mode. These machines can be limited by beam-breakup instability at high currents because higher-order modes with very high Q factors are easily excited by the beam. Photonic band gap (PBG) structures provide a way to strongly damp higher-order modes without compromising the performance of the structure in the fundamental mode. We first address the design of the structure and issues that arise from incorporating a complex PBG cell into an SRF module. In particular, the module was tuned to have uneven accelerating gradient profile in order to provide equal peak surface magnetic field in every cell. We then cover the fabrication steps and surface treatment of the five-cell niobium structure and report results of the high gradient tests at temperatures of 4 K and 2 K.
	Slides WEA2A02 [7.023 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA04	Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities	1006
	K. Umemori, H. Inoue, T. Kubo, H. Shimizu, Y. Watanabe, M. Yamanaka KEK, Ibaraki, Japan A. Hocker Fermilab, Batavia, Illinois, USA T. Tajima LANL, Los Alamos, New Mexico, USA
	In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented.
	Slides THAA04 [2.810 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB041	Hydroforming SRF Cavities from Seamless Niobium Tubes	1176
	M. Yamanaka, H. Inoue, H. Shimizu, K. Umemori KEK, Ibaraki, Japan A. Hocker Fermilab, Batavia, Illinois, USA T. Tajima LANL, Los Alamos, New Mexico, USA
	The authors are developing the manufacturing method for super conducting radio frequency (SRF) cavities by using a hydroforming instead of an electron beam welding, which is the major manufacturing method. We expect a cost reduction by hiring the hydroforming. To realize this development, getting a high-purity seamless niobium tube with good forming ability and an advancement of hydroforming technique are necessary. We got the seamless niobium tube made by ATI Wah Chang with the cooperation of Fermilab, and succeeded to manufacture the 1-cell cavity by hydroforming. The accelerating gradient attained to 36 MV/m, and we confirmed it was available to use as the SRF cavity.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

Paper

Title

Page

Increase in Vortex Penetration Field on Nb Ellipsoid Coated With a MbB2 Thin Film

512

T. Tan, M.A. Wolak, X. Xi
Temple University, Philadelphia, USA
L. Civale, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: DOE Office of Science/High Energy Physics
Since SRF2013, there has been a remarkable progress in terms of sample measurement. Instead of measuring a flat film that allows magnetic field on both sides of the film, which does not simulate the situation on a SRF cavity correctly, an ellipsoidal bulk Nb (rugby-ball shape with ~8 mm long axis) was coated with a MgB2 film and its vortex penetration field has been measured with a SQUID magnetometer and compared with uncoated samples. After a number of measurements, vortex penetration field has been consistent with maximum critical RF field, superheating field. Here, we show that 100 nm and 200 nm thick MgB2 coating increases the vortex penetration field by up to ~70 mT, e.g., 240 mT (200 nm MgB2 coated Nb) vs. 170 mT (uncoated Nb) at 2.8 K (lowest measurement temperature) with the trend of increasing as temperature goes down. This is consistent with recent theoretical development saying that the increase is possible even without an insulation layer, which makes the coating easier. In this talk, the thickness dependence of the rise and comparison with theory will be shown.

Slides TUBA06 [2.088 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB053

Research on MgB2 at LANL for the Application to SRF Structures

700

T. Tajima, L. Civale, R.K. Schulze
LANL, Los Alamos, New Mexico, USA

Funding: U.S. Department of Energy (DOE) Office of Science Office of Nuclear Physics Early Career Research Program
This paper is focused on the development of MgB2 coating technique at LANL. Using boron film samples obtained at a large furnace system, we succeeded in obtaining superconducting MgB2 films (Tc of up to 37 K so far) by reacting them with Mg vapor. The major improvements were 1) confinement of the Mg vapor in a hot zone to mitigate the insufficient Mg pressure due to condensation on low temperature surfaces of the connected vacuum pipes and 2) reduction of cooldown time, i.e., ~13 minutes instead of ~1 day with the large system to prevent MgB2 from decomposing.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA2A02

High Gradient Testing of the Five-Cell Superconducting RF Module With a PBG Coupler Cell

948

S. Arsenyev
MIT/PSFC, Cambridge, Massachusetts, USA
C.H. Boulware, T.L. Grimm, A. Rogacki
Niowave, Inc., Lansing, Michigan, USA
W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: DOE Office of Science/Office of High Energy Physics
Superconducting radio-frequency (SRF) accelerating structures allow high-gradient operation in continuous-wave mode. These machines can be limited by beam-breakup instability at high currents because higher-order modes with very high Q factors are easily excited by the beam. Photonic band gap (PBG) structures provide a way to strongly damp higher-order modes without compromising the performance of the structure in the fundamental mode. We first address the design of the structure and issues that arise from incorporating a complex PBG cell into an SRF module. In particular, the module was tuned to have uneven accelerating gradient profile in order to provide equal peak surface magnetic field in every cell. We then cover the fabrication steps and surface treatment of the five-cell niobium structure and report results of the high gradient tests at temperatures of 4 K and 2 K.

Slides WEA2A02 [7.023 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA04

Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities

1006

K. Umemori, H. Inoue, T. Kubo, H. Shimizu, Y. Watanabe, M. Yamanaka
KEK, Ibaraki, Japan
A. Hocker
Fermilab, Batavia, Illinois, USA
T. Tajima
LANL, Los Alamos, New Mexico, USA

In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented.

Slides THAA04 [2.810 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB041

Hydroforming SRF Cavities from Seamless Niobium Tubes

1176

M. Yamanaka, H. Inoue, H. Shimizu, K. Umemori
KEK, Ibaraki, Japan
A. Hocker
Fermilab, Batavia, Illinois, USA
T. Tajima
LANL, Los Alamos, New Mexico, USA

The authors are developing the manufacturing method for super conducting radio frequency (SRF) cavities by using a hydroforming instead of an electron beam welding, which is the major manufacturing method. We expect a cost reduction by hiring the hydroforming. To realize this development, getting a high-purity seamless niobium tube with good forming ability and an advancement of hydroforming technique are necessary. We got the seamless niobium tube made by ATI Wah Chang with the cooperation of Fermilab, and succeeded to manufacture the 1-cell cavity by hydroforming. The accelerating gradient attained to 36 MV/m, and we confirmed it was available to use as the SRF cavity.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)