Flux pinning by symmetrical grain boundaries in niobium bicrystals

Cai, Bin; Chou, Y. T.; Gupta, Amit

doi:10.1080/13642818708211256

Cited by 14 publications

(8 citation statements)

References 13 publications

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“…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%

“…This irregular spacing results into lattice distortion that strongly depends on the relative orientations of the grains. GB are usually expected to be effective vortex traps [4,12]. Note that only a few relative orientations give rise to high disorder [58].…”

Section: B Grain Boundariesmentioning

confidence: 99%

“…Several experiments demonstrated indeed some weakening of superconductivity at GB. In particular early field penetration can be observed in GB when exposed to magnetic field, forming Josephson vortices with penetration field ∼1=3 of the bulk value [12,[60][61][62][63], the effect being maximum when the field is parallel to the field plane [3,60,63]. Grain boundary pinning has been observed and measured on Nb [12,64], and appears to depend on the grain size.…”

Section: B Grain Boundariesmentioning

confidence: 99%

“…In particular early field penetration can be observed in GB when exposed to magnetic field, forming Josephson vortices with penetration field ∼1=3 of the bulk value [12,[60][61][62][63], the effect being maximum when the field is parallel to the field plane [3,60,63]. Grain boundary pinning has been observed and measured on Nb [12,64], and appears to depend on the grain size. It is believed that large grain material tends to exhibit a slightly higher medium field Q value than fine grain material [24,[65][66][67], because it has less GB.…”

Section: B Grain Boundariesmentioning

confidence: 99%

“…The elementary pinning force per unit length of flux line f P has been measured in Nb bicrystals of various relative orientations and it is about 7 × 10 −6 N=m when the field is aligned parallel to the GB [12], to be compared to values for GB pinning in Nb 3 Sn that range between 6 × 10 −5 and 10 −4 N=m [64], up to 4 × 10 −4 N=m for MgB 2 [4] and 9.1 × 10 −4 N=m for a normal conducting precipitate [4]. The difference in the pinning forces between GB and normal conducting precipitates arises mainly from the fact that in GB the main mechanism is electron scattering whereas in normal conducting areas, the dominant mechanism is the savings in condensation energy [4].…”

Section: B Grain Boundariesmentioning

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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