Magnetic properties and hydrides precipitation observation of nitrogen doping niobium used for accelerator applications

Yang, Ziqin; Lu, Xiangyang; He, Yuan; Tan, Weiwei; Huang, Shijie; Guo, Hao

doi:10.1016/j.rinp.2019.02.073

Cited by 3 publications

(4 citation statements)

References 40 publications

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“…there is clear evidence that even extremely low oxygen pressures lead to a substantial oxidation of Nb at temperatures of 900 C. On the other hand, as the vacuum pressure within the newly developed cell is around 2 Â 10 À6 to 3 Â 10 À6 mbar even for temperatures in the range 800-900 C, such an oxide growth can be further suppressed to uncritical values, as discussed in Section 4.1. These results are of special importance for all treatments of niobium at elevated temperatures, in particular for the nitridation of superconducting radiofrequency Nb cavities [N-doping (Grassellino et al, 2013, Gonnella & Liepe, 2014Gonnella et al, 2015;Yang et al, 2019)], where the pre-heating treatments of the cavities should be carried out using best-possible vacuum conditions according to the results presented here.…”

Section: Figurementioning

confidence: 79%

“…Such a nitrogen doping has been proven to be profitable for the superconducting properties of Nb in accelerating structures (see, for example, Grassellino et al, 2013;Gonnella & Liepe, 2014;Gonnella et al, 2015). Recent experiments have shown that extreme care has to be used for such a high-temperature processing of Nb cavity materials, and that, for example, traces of oxygen, carbon contaminations or remaining hydrogen from outgassing of the vacuum system may substantially alter the near-surface structure and thereby also the superconducting properties of heat-treated Nb materials (Yang et al, 2018(Yang et al, , 2019Dhakal et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…In particular for studies of processes employed for thermal treatments of superconducting RF cavities, contaminations such as oxide layers on the surfaces are not tolerable at all, as they substantially degrade the superconducting performance of the devices (see, for example, Malev & Weisser, 1995;Yang et al, 2018;Dhakal et al, 2018;Yang et al, 2019). All preparation steps and protocols have to be highly reliable, and any oxidation has to be avoided in the processing of cavity materials.…”

Section: Introductionmentioning

confidence: 99%

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High-temperature treatments of niobium under high vacuum, dilute air- and nitrogen-atmospheres as investigated by in situ X-ray absorption spectroscopy

Klaes

Rothweiler

Bornmann

et al. 2021

J Synchrotron Radiat

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Niobium metal foils were heat-treated at 900°C under different conditions and in situ investigated with time-resolved X-ray absorption fine-structure (EXAFS and XANES) measurements. The present study aims to mimic the conditions usually applied for heat treatments of Nb materials used for superconducting radiofrequency cavities, in order to better understand the evolving processes during vacuum annealing as well as for heat treatments in controlled dilute gases. Annealing in vacuum in a commercially available cell showed a substantial amount of oxidation, so that a designated new cell was designed and realized, allowing treatments under clean high-vacuum conditions as well as under well controllable gas atmospheres. The experiments performed under vacuum demonstrated that the original structure of the Nb foils is preserved, while a detailed evaluation of the X-ray absorption fine-structure data acquired during treatments in dilute air atmospheres (10−5 mbar to 10−3 mbar) revealed a linear oxidation with the time of the treatment, and an oxidation rate proportional to the oxygen (air) pressure. The structure of the oxide appears to be very similar to that of polycrystalline NbO. The cell also permits controlled exposures to other reactive gases at elevated temperatures; here the Nb foils were exposed to dilute nitrogen atmospheres after a pre-conditioning of the studied Nb material for one hour under high-vacuum conditions, in order to imitate typical conditions used for nitrogen doping of cavity materials. Clear structural changes induced by the N2 exposure were found; however, no evidence for the formation of niobium nitride could be derived from the EXAFS and XANES experiments. The presented results establish the feasibility to study the structural changes of the Nb materials in situ during heat treatments in reactive gases with temporal resolution, which are important to better understand the underlaying mechanisms and the dynamics of phase formation during those heat treatments in more detail.

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Section: Figurementioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

High-temperature treatments of niobium under high vacuum, dilute air- and nitrogen-atmospheres as investigated by in situ X-ray absorption spectroscopy

Klaes

Rothweiler

Bornmann

et al. 2021

J Synchrotron Radiat

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show abstract

“…The measurement showed that Hffp is lowered by ~ 15% due to the nitrogen doping (Fig. 14) [100,101,102] with no significant change in the bulk superconducting properties, confirming that the doping volume is smaller compared to the sample size.…”

Section: DC Magnetization and Ac Susceptibilitymentioning

confidence: 91%

Nitrogen doping and infusion in SRF cavities: A review

Dhakal

2020

Physics Open

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Characterization of dissipative regions of a N-doped superconducting radio-frequency cavity

Lechner

Oli

Makita

et al. 2023

Front. Electron. Mater

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We report radio-frequency measurements of quality factors and temperature mapping of a nitrogen doped Nb superconducting RF cavity. Cavity cutouts of hot and cold spots were studied with low temperature scanning tunneling microscopy and spectroscopy, X-ray photoelectron spectroscopy and secondary electron microscopy. Temperature mapping revealed a substantial reduction of the residual resistance upon cooling the cavity with a greater temperature gradient and hysteretic losses at the quench location, pointing to trapped vortices as the dominant source of residual surface resistance. Analysis of the tunneling spectra in the framework of a proximity effect theory shows that hot spots have a reduced pair potential and a wider distribution of the contact resistance between the Nb and the top Nb oxide. Alone, these degraded superconducting properties account for a much weaker excess dissipation as compared with the vortex contribution. Based on the correlation between the quasiparticle density of states and temperature mapping, we suggest that degraded superconducting properties may facilitate vortex nucleation or settling of trapped flux during cooling the cavity through the critical temperature.

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Magnetic properties and hydrides precipitation observation of nitrogen doping niobium used for accelerator applications

Cited by 3 publications

References 40 publications

High-temperature treatments of niobium under high vacuum, dilute air- and nitrogen-atmospheres as investigated by in situ X-ray absorption spectroscopy

High-temperature treatments of niobium under high vacuum, dilute air- and nitrogen-atmospheres as investigated by in situ X-ray absorption spectroscopy

Nitrogen doping and infusion in SRF cavities: A review

Characterization of dissipative regions of a N-doped superconducting radio-frequency cavity

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