Outgassing rate comparison of seven geometrically similar vacuum chambers of different materials and heat treatments

The 3 GeV electron storage ring of the MAX IV laboratory is the first storage-ring-based synchrotron radiation facility with the inner surface of almost all the vacuum chambers along its circumference coated with non-evaporable getter (NEG) thin film. The coating provides a low dynamic outgassing rate and pumping of active gases. As the NEG coating was applied on an unprecedented scale, there were doubts concerning the storage ring performance. Fast conditioning of the vacuum system and over five years of reliable accelerator operation have demonstrated that the chosen design proved to be good and does not impose limits on the operation. The vacuum system performance is comparable with or better than that of other similar facilities around the world, where conventional designs were implemented. Observed pressure levels are low, and the electron beam lifetime is long and not limited by residual gas density. A summary of the vacuum performance is presented.

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Influence of Heat Treatments on Microstructures in an Fe-Co-V Alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052572 ◽

1974 ◽

Vol 32 ◽

pp. 512-513

Author(s):

S. Mahajan ◽

M. R. Pinnel ◽

J. E. Bennett

Keyword(s):

Single Phase ◽

Alloy Composition ◽

Supersaturated Solid Solution ◽

Cell Formation ◽

Heat Treatments ◽

Air Cooling ◽

Iced Brine ◽

Transmission Electron ◽

The Matrix ◽

Bcc Structure

The microstructural changes in an Fe-Co-V alloy (composition by wt.%: 2.97 V, 48.70 Co, 47.34 Fe and balance impurities, such as C, P and Ni) resulting from different heat treatments have been evaluated by optical metallography and transmission electron microscopy. Results indicate that, on air cooling or quenching into iced-brine from the high temperature single phase ϒ (fcc) field, vanadium can be retained in a supersaturated solid solution (α2) which has bcc structure. For the range of cooling rates employed, a portion of the material appears to undergo the γ-α2 transformation massively and the remainder martensitically. Figure 1 shows dislocation topology in a region that may have transformed martensitically. Dislocations are homogeneously distributed throughout the matrix, and there is no evidence for cell formation. The majority of the dislocations project along the projections of <111> vectors onto the (111) plane, implying that they are predominantly of screw character.

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Microstructural Development in Nb-Ti Multifilamentary Superconductors During Processing

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117911 ◽

1985 ◽

Vol 43 ◽

pp. 190-191

Author(s):

A. W. West

Keyword(s):

Heat Treatment ◽

Critical Current Density ◽

Copper Matrix ◽

Wire Drawing ◽

Heat Treatments ◽

Microstructural Development ◽

Final Size ◽

Density Values ◽

The Wire ◽

Multifilamentary Superconductors

The influence of the filament microstructure on the critical current density values, Jc, of Nb-Ti multifilamentary superconducting composites has been well documented. However the development of these microstructures during composite processing is still under investigation.During manufacture, the multifilamentary composite is given several heat treatments interspersed in the wire-drawing schedule. Typically, these heat treatments are for 5 to 80 hours at temperatures between 523 and 573K. A short heat treatment of approximately 3 hours at 573K is usually given to the wire at final size. Originally this heat treatment was given to soften the copper matrix, but recent work has shown that it can markedly change both the Jc value and microstructure of the composite.

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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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