High gradient studies for ILC with single-cell re-entrant shape and elliptical shape cavities made of fine-grain and large-grain niobium

A circular electron positron collider (CEPC) will adopt hundreds of 650-MHz superconducting cavities with high quality factor (Q) and accelerating gradient (Eacc). Two 650-MHz single-cell cavities made of fine-grain niobium were first treated via buffered chemical polishing (BCP), which was easy and convenient. However, the vertical test results could not meet the specification of the CEPC (4 × 1010 at 22 MV/m). Therefore, electro-polishing (EP) of 650-MHz single-cell cavities was conducted, which was complicated but remarkably effective. Both 650-MHz single-cell cavities achieved state-of-the-art gradients of 35 MV/m after the EP process, which is extremely high for large elliptical cavities (frequency < 1 GHz). One cavity achieved an intrinsic quality factor (Q0) of 4.5 × 1010 at 22.0 MV/m, which was higher than the CEPC spec. The other cavity obtained a lower Q0 of 3.4 × 1010 at 22.0 MV/m, which may have resulted from the cancellation of high-temperature annealing.

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Aspects of microanalysis in a transmission electron microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109690 ◽

1978 ◽

Vol 36 (1) ◽

pp. 510-511

Author(s):

R. Sinclair ◽

B.E. Jacobson

Keyword(s):

Grain Size ◽

Electron Beam ◽

Electron Microscope ◽

Chemical Analysis ◽

Transmission Electron Microscope ◽

Vapor Deposition ◽

Critical Currents ◽

X Ray ◽

Fine Grain ◽

Transmission Electron

INTRODUCTIONThe prospect of performing chemical analysis of thin specimens at any desired level of resolution is particularly appealing to the materials scientist. Commercial TEM-based systems are now available which virtually provide this capability. The purpose of this contribution is to illustrate its application to problems which would have been intractable until recently, pointing out some current limitations.X-RAY ANALYSISIn an attempt to fabricate superconducting materials with high critical currents and temperature, thin Nb3Sn films have been prepared by electron beam vapor deposition [1]. Fine-grain size material is desirable which may be achieved by codeposition with small amounts of Al2O3 . Figure 1 shows the STEM microstructure, with large (∽ 200 Å dia) voids present at the grain boundaries. Higher quality TEM micrographs (e.g. fig. 2) reveal the presence of small voids within the grains which are absent in pure Nb3Sn prepared under identical conditions. The X-ray spectrum from large (∽ lμ dia) or small (∽100 Ǻ dia) areas within the grains indicates only small amounts of A1 (fig.3).

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Superior 2X2 Slides

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100114414 ◽

1975 ◽

Vol 33 ◽

pp. 158-159

Author(s):

Harry Schaefer ◽

Bruce Wetzel

Keyword(s):

New York ◽

High Resolution ◽

Black And White ◽

Fine Grain ◽

White Film

High resolution 24mm X 36mm positive transparencies can be made from original black and white negatives produced by SEM, TEM, and photomicrography with ease, convenience, and little expense. The resulting 2in X 2in slides are superior to 3¼in X 4in lantern slides for storage, transport, and sturdiness, and projection equipment is more readily available. By mating a 35mm camera directly to an enlarger lens board (Fig. 1), one combines many advantages of both. The negative is positioned and illuminated with the enlarger and then focussed and photographed with the camera on a fine grain black and white film.Specifically, a Durst Laborator 138 S 5in by 7in enlarger with 240/200 condensers and a 500 watt Opale bulb (Ehrenreich Photo-Optical Industries, Inc., New York, NY) is rotated to the horizontal and adjusted for comfortable eye level viewing.

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Electron microscopy of keratinocytes cultured on a collagen substrate used as an allograft for the treatment of chronic wounds

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130158 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1104-1105

Author(s):

Debby A. Jennings ◽

Michael J. Morykwas ◽

Louis C. Argenta

Keyword(s):

Electron Microscopy ◽

Cell Suspension ◽

Single Cell ◽

Chronic Wounds ◽

Mechanical Stability ◽

Uv Light ◽

Type I ◽

Single Cell Suspension ◽

Collagen Substrate ◽

Dermal Collagen

Grafts of cultured allogenic or autogenic keratlnocytes have proven to be an effective treatment of chronic wounds and burns. This study utilized a collagen substrate for keratinocyte and fibroblast attachment. The substrate provided mechanical stability and augmented graft manipulation onto the wound bed. Graft integrity was confirmed by light and transmission electron microscopy.Bovine Type I dermal collagen sheets (100 μm thick) were crosslinked with 254 nm UV light (13.5 Joules/cm2) to improve mechanical properties and reduce degradation. A single cell suspension of third passage neonatal foreskin fibroblasts were plated onto the collagen. Five days later, a single cell suspension of first passage neonatal foreskin keratinocytes were plated on the opposite side of the collagen. The grafts were cultured for one month.The grafts were fixed in phosphate buffered 4% formaldehyde/1% glutaraldehyde for 24 hours. Graft pieces were then washed in 0.13 M phosphate buffer, post-fixed in 1% osmium tetroxide, dehydrated, and embedded in Polybed 812.

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Microstructure Development in a High Current Density NbTi Superconducting Composite

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010011790x ◽

1985 ◽

Vol 43 ◽

pp. 186-189

Author(s):

P. J. Lee ◽

D. C. Larbalestier

Keyword(s):

Current Density ◽

High Current Density ◽

Cold Drawing ◽

Heat Treatments ◽

Grain Structure ◽

Fine Grain ◽

Boundary Film ◽

Quantitative Basis ◽

Cold Worked ◽

Very High

Several features of the metallurgy of superconducting composites of Nb-Ti in a Cu matrix are of interest. The cold drawing strains are generally of order 8-10, producing a very fine grain structure of diameter 30-50 nm. Heat treatments of as little as 3 hours at 300 C (∼ 0.27 TM) produce a thin (1-3 nm) Ti-rich grain boundary film, the precipitate later growing out at triple points to 50-100 nm dia. Further plastic deformation of these larger a-Ti precipitates by strains of 3-4 produces an elongated ribbon morphology (of order 3 x 50 nm in transverse section) and it is the thickness and separation of these precipitates which are believed to control the superconducting properties. The present paper describes initial attempts to put our understanding of the metallurgy of these heavily cold-worked composites on a quantitative basis. The composite studied was fabricated in our own laboratory, using six intermediate heat treatments. This process enabled very high critical current density (Jc) values to be obtained. Samples were cut from the composite at many processing stages and a report of the structure of a number of these samples is made here.

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