Flux-pinning in multifilament niobium by dislocation cell boundaries

Santhanam, A. T.

doi:10.1007/bf02396644

Cited by 14 publications

(7 citation statements)

References 7 publications

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“…All vortice lines at a short distance from the wall get attracted there. Similar effects have been observed in [14,82]. In [14], Sathanam draws a correlation between J C (which is proportional to the pinning force F P ) and the mean size of dislocation cells.…”

Section: Dislocationssupporting

confidence: 67%

“…Similar effects have been observed in [14,82]. In [14], Sathanam draws a correlation between J C (which is proportional to the pinning force F P ) and the mean size of dislocation cells. He found that F P is maximum for dislocation cells about 100 nm, which is precisely the same order of magnitude as 2ξ.…”

Section: Dislocationssupporting

confidence: 67%

“…Pinning behavior of crystalline defects has been thoroughly studied from the theoretical point of view during the development of SC cable (see textbooks, e.g., [3,4,11]); a lot of data can be found on Nb, bulk as well as thin films in the literature (e.g., [12][13][14][15][16]). The detail of the physical phenomena implied in the pinning behavior can also be used to explain the very type of behavior observed on cavities, such as hydride precipitates or lab to lab performance variability.…”

Section: B Generalities On Pinningmentioning

confidence: 99%

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Influence of crystalline structure on rf dissipation in superconducting niobium

Antoine

2019

Phys. Rev. Accel. Beams

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Bulk niobium is the most common material used in the fabrication of rf superconducting cavities for accelerators. Predicting and reducing the rf surface dissipation in these cavity structures is mandatory, since it has a tremendous cost impact on the large accelerator projects. In this paper the author hopes to demonstrate that sources of dissipation usually attributed to external causes (mainly flux trapping during cooldown and hydrides precipitates) are related to the same type of crystalline defects that affect the local superconducting properties and can be at the source of early vortex penetration at the surface. We also want to show how these types of defects can explain some of the discrepancies observed from other laboratories in niobium cavity doping experiments. Understanding the origin and the role of these defects could provide direction for improving material specifications as well as improving fabrication control from sheet material to completed cavity. In particular, we will demonstrate that dislocation entanglements, due to the fabrication damage layer, have the strongest impact for the pinning behavior of trapped flux, as well as hydrogen segregation in cavity niobium. The author wishes to present to the superconducting radio frequency (SRF) accelerator community the synthesis of experimental results scattered in the literature, completed with some personal results. The results of this effort provide a new perspective on recently published work in the domain of SRF cavity doping and sensitivity to trapped flux during cooldown. I will also try to draw whenever possible, some conclusions about other types of superconductors used for SRF applications including Nb=Cu thin films and to discuss their possible change of behavior with field or frequency. I will concentrate on surface and material science aspects since the experimental results on rf cavities have already been treated elsewhere.

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Section: Dislocationssupporting

confidence: 67%

Section: Dislocationssupporting

confidence: 67%

Section: B Generalities On Pinningmentioning

confidence: 99%

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Influence of crystalline structure on rf dissipation in superconducting niobium

Antoine

2019

Phys. Rev. Accel. Beams

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“…Material with larger grains appeared to have higher expulsion, which is consistent with the results in Figure 3, as well as with previous studies of high field pinning. 12,13 However, even in single crystal niobium samples, heat treatment appeared to improve expulsion, suggesting that crystal properties other than grain boundaries (e.g., dislocations) play an important role. 25 We can apply a simple model to attempt to predict the quality factor that would be achieved in the cavities from production groups 1 and 2, depending on the temperature gradient applied during cooldown (converting from DT using the approximate distance between thermometers of 20 cm).…”

Section: -4mentioning

confidence: 99%

“…The goal of the study was to determine whether flux trapping behavior is determined by bulk properties (e.g. grain boundaries, as in [11,12]) or surface properties (e.g. nitrides from the nitrogen-doping process) and then to find a treatment that improves expulsion.…”

mentioning

confidence: 99%

Efficient expulsion of magnetic flux in superconducting radiofrequency cavities for high Q applications

Posen

Checchin

Crawford

et al. 2016

Journal of Applied Physics

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Even when cooled through its transition temperature in the presence of an external magnetic field, a superconductor can expel nearly all external magnetic flux. This Letter presents an experimental study to identify the parameters that most strongly influence flux trapping in high purity niobium during cooldown. This is critical to the operation of superconducting radiofrequency cavities, in which trapped flux degrades the quality factor and therefore cryogenic efficiency. Flux expulsion was measured on a large survey of 1.3 GHz cavities prepared in various ways. It is shown that both spatial thermal gradient and high temperature treatment are critical to expelling external magnetic fields, while surface treatment has minimal effect. For the first time, it is shown that a cavity can be converted from poor expulsion behavior to strong expulsion behavior after furnace treatment, resulting in a substantial improvement in quality factor. Future plans are described to build on this result in order to optimize treatment for future cavities.

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30Mei1 - 73Kit1

Flükiger¹,

Wolf²

Landolt-Börnstein - Group III Condensed Matter

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Flux-pinning in multifilament niobium by dislocation cell boundaries

Cited by 14 publications

References 7 publications

Influence of crystalline structure on rf dissipation in superconducting niobium

Influence of crystalline structure on rf dissipation in superconducting niobium

Efficient expulsion of magnetic flux in superconducting radiofrequency cavities for high Q applications

30Mei1 - 73Kit1

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