Precipitation of hydrides in high purity niobium after different treatments

Barkov, F. L.; Romanenko, Alexander; Trenikhina, Yulia; Grassellino, Anna

doi:10.1063/1.4826901

Cited by 39 publications

(48 citation statements)

References 28 publications

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“…Small nanoscale hydrides have been lately proposed to be the cause of the anomalous high field dissipa-tion [30], and the 120 ○ C baking effect attributed to the injection of vacancies [31]. Preliminary structural investigations [32,33] are also consistent with this picture. Within this model hydrides remain superconducting by proximity effect up to the high field dissipation onset (B rf ∼100 mT), which is consistent with the clean limit Pippard/BCS description at B ≤ 25 mT of LE-µSR data for the hot region (100-6).…”

mentioning

confidence: 80%

Strong Meissner screening change in superconducting radio frequency cavities due to mild baking

Romanenko

Grassellino

Barkov

et al. 2014

Applied Physics Letters

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We investigate "hot" regions with anomalous high field dissipation in bulk niobium superconducting radio frequency cavities for particle accelerators by using low energy muon spin rotation (LE-µSR) on corresponding cavity cutouts. We demonstrate that superconducting properties at the hot region are well described by the non-local Pippard/BCS model for niobium in the clean limit with a London penetration depth λ L = 23 ± 2 nm. In contrast, a cutout sample from the 120 ○ C baked cavity shows a much larger λ > 100 nm and a depth dependent mean free path, likely due to gradient in vacancy concentration. We suggest that these vacancies can efficiently trap hydrogen and hence prevent the formation of hydrides responsible for rf losses in hot regions.

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confidence: 80%

Strong Meissner screening change in superconducting radio frequency cavities due to mild baking

Romanenko

Grassellino

Barkov

et al. 2014

Applied Physics Letters

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“…7,13,20 At this stage, it is not yet possible to definitively say, if it is the volume density or the size of the nanohydrides, which is affected. However, the removal of the HFQS suggests that it is likely the size.…”

Section: Discussionmentioning

confidence: 99%

“…SRF cavities have operational temperatures in the range of 1.2-4.2 K, while all hydride precipitation happens during the cool-down at much higher temperatures of 100-150 K as follows from NbH phase diagram 19 and confirmed by recent direct optical investigations. 20 Thus observing at 94 K is fully representative of the hydride state inside niobium at lower temperatures.…”

Section: -2mentioning

confidence: 99%

Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by transmission electron microscopy and electron energy loss spectroscopy

Trenikhina

Romanenko

Kwon

et al. 2015

Journal of Applied Physics

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Nanoscale defect structure within the magnetic penetration depth of ∼100 nm is key to the performance limitations of niobium superconducting radio frequency (SRF) cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls, we discover the existence of nanoscale hydrides in electropolished cavities limited by the high field Q slope, and show the decreased hydride formation in the electropolished cavity after 120 • C baking. Furthermore, we demonstrate that adding 800 • C hydrogen degassing followed by light buffered chemical polishing restores the hydride formation to the pre-120 • C bake level. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120 • C bake.

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“…Nevertheless, annealed cavities are much less sensitive to hydrogen uptake during subsequent chemical polishing. This is probably related to the fact that the annealing allows the lattice to recrystallize and/or recover, and thus the quantity of crystalline defects, in particular dislocations are tremendously reduced, leaving less preferential sites for segregation [136,137]. One argument that supports further the recrystallization hypothesis is that the couples "times þ temperature" observed to remove Q-disease are typically those known for recrystallization: the relationship between time (t R ) and temperature (T R ) to achieve a given recrystallization state R is in the form of [138] log…”

Section: B Heat Treatments: Necessary But Not Fully Efficientmentioning

confidence: 99%

“…Nevertheless, even if heat treatment gets rid of heavy Q-disease, experimental facts described in the previous sections indicate that it is not possible to eliminate all the crystalline defects, and some hydrogen remains. There are some indications that different kinds of hydrides form depending on whether the H content is low or high and on the crystalline state of the surface [136].…”

Section: B Heat Treatments: Necessary But Not Fully Efficientmentioning

confidence: 99%

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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Precipitation of hydrides in high purity niobium after different treatments

Cited by 39 publications

References 28 publications

Strong Meissner screening change in superconducting radio frequency cavities due to mild baking

Strong Meissner screening change in superconducting radio frequency cavities due to mild baking

Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by transmission electron microscopy and electron energy loss spectroscopy

Influence of crystalline structure on rf dissipation in superconducting niobium

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