Dislocation arrangement and flux pinning in deformed niobium single crystals

Schlump, W.; Freyhardt, H.C.; Nembach, E.

doi:10.1016/0001-6160(72)90188-5

Cited by 9 publications

(3 citation statements)

References 15 publications

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“…5 is obtained for 10 8 & N d & 5 Â 10 9 cm À2 . These orders of magnitude of N d are in excellent agreement with those found for niobium monocrystals having undergone <15% deformations [7,18]. Our analysis clearly illustrates the important role of dislocations for monocrystalline niobium in the temperature range 1.5-2.5 K. For completeness, we add that undeformed Nb single crystals generally have dislocations densities of 10 5 -10 7 cm À2 after a heat treatment [11].…”

Section: A Thermal Conductivitysupporting

confidence: 86%

“…This aspect requires new systematic experimental investigations. However, it is well known that a heat treatment (annealing) drastically reduces the dislocation density by a factor of 10-100 [11,18]. Consequently, we believe that a mechanically polished Nb single crystal which has under-gone a heat treatment shall have a better efficiency in thermal evacuation than a chemically polished Nb single crystal.…”

Section: B Kapitza Resistancementioning

confidence: 94%

“…However, it is not evident that the effective heat transfer from the Nb crystal to the superfluid helium would be more efficient in the case of mechanically polished samples. This is so because mechanically polished Nb single crystal samples have a high density of dislocations [18] which decreases the thermal conductivity (see curve c in Fig. 5).…”

Section: B Kapitza Resistancementioning

confidence: 99%

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Kapitza resistance cooling of single crystal (111) niobium for superconducting rf cavities

Amrit

Antoine

2010

Phys. Rev. ST Accel. Beams

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The use of large grains or single crystal niobium to improve the Q factor of superconducting rf cavities for particle accelerators, is presently under study. Heat extraction which plays a decisive role in the thermomagnetic stability of these devices depends on the thermal conductivity of niobium K and the thermal boundary (Kapitza) resistance R K at the niobium/superfluid helium interface. Here we present the first measurements of R K performed between 1.5-2.1 K with single crystal (111) niobium, having two different surface morphologies, namely, a surface with a damage layer and a chemically polished surface. The thermal conductivity of the single crystal Nb samples is also simultaneously determined. For monocrystalline niobium we demonstrate that R K is an increasing primary limiting factor with temperature, contrary to the behavior found for polycrystalline cavities. The present investigation reveals for the first time that the presence of impurities (metallic particles and oxygen) within the damage layer leads to a stronger R K , although the effective heat exchange area to the superfluid is increased. We further show the importance of dislocations in the thermal conductivity of monocrystalline niobium.

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Section: A Thermal Conductivitysupporting

confidence: 86%

Section: B Kapitza Resistancementioning

confidence: 94%

Section: B Kapitza Resistancementioning

confidence: 99%

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Kapitza resistance cooling of single crystal (111) niobium for superconducting rf cavities

Amrit

Antoine

2010

Phys. Rev. ST Accel. Beams

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Anisotropic critical currents in heterogeneous lead–sodium alloys

Schultz

Freyhardt

1972

Phys. Stat. Sol. (a)

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Measurements of the transverse critical current densities ic are reported in type II superconducting Pb‐8.4 at% Na alloys containing precipitates of a Pb3Na phase. Small precipitates are randomly distributed, larger ones are aligned in the 〈100〉 directions. The ic versus H curves depend on the crystallographic orientation of the external magnetic field H and show a peak‐effect which can be explained by a geometrical matching of the regular precipitate and flux line arrangements. It appears necessary to take into account proximity effects between the precipitated phase and the matrix.

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Field history effect of the flux gradient in superconducting niobium

1978

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The flux density gradient in a plastically deformed niobium single crystal was measured. The profiles in increasing and decreasing field are not symmetric, and depend on the history of the magnetic field. This effect was observed up to 0.9Hc2, although it was more pronounced at lower fields. These results, as well as an observed asymmetry of minor hysteresis loops, cannot be understood by the critical state model. We suggest that they are related to the creation of dislocations in the flux line lattice.

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Dislocation arrangement and flux pinning in deformed niobium single crystals

Cited by 9 publications

References 15 publications

Kapitza resistance cooling of single crystal (111) niobium for superconducting rf cavities

Kapitza resistance cooling of single crystal (111) niobium for superconducting rf cavities

Anisotropic critical currents in heterogeneous lead–sodium alloys

Field history effect of the flux gradient in superconducting niobium

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