Muon diffusion in niobium in the presence of traps

Niinikoski, T.; Hartmann, O.; Karlsson, E.; Norlin, L. O.; Pernestl, K.; Kehr, K. W.; Richter, D.; Wałker, E.; Schulze, K.

doi:10.1007/bf01028797

Cited by 27 publications

(15 citation statements)

References 5 publications

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“…The total impurity concentration of the samples analyzed here can be estimated to be in the 1000 ppm range [32]. A sample with such a high interstitial impurity concentration has been analyzed in [44]. The depolarization rate found was similar as for material of higher purity at low temperature in accordance with the expectation for static muons.…”

Section: Longitudinal Field Studies Of the Hipims Samplesupporting

confidence: 80%

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A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

Junginger

Calatroni

Sublet

et al. 2017

Supercond. Sci. Technol.

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Point contact tunneling (PCT) and low energy muon spin rotation (LE-µSR) are used to probe, on the same samples, the surface superconducting properties of micrometer thick niobium films deposited onto copper substrates using different sputtering techniques: diode, dc magnetron (dcMS) and HIPIMS. The combined results are compared to radio-frequency tests performances of RF cavities made with the same processes. Degraded surface superconducting properties are found to correlate to lower quality factors and stronger Q slope. In addition, both techniques find evidence for surface paramagnetism on all samples and particularly on Nb films prepared by HIPIMS. I. CURRENT LIMITATIONS OF NIOBIUM ON COPPER CAVITIESSuperconducting cavities prepared by coating a micrometer thick niobium film on a copper substrate enable a lower surface resistance compared to bulk niobium at 4.5 K the operation temperature of several accelerators using this technology, like the LHC or the HIE-Isolde at CERN. Additionally Nb/Cu cavities are more costeffective and do not require magnetic shielding. Thermal stability is enhanced avoiding quenches [1].Despite these advantages, this technology is currently not being considered for accelerators requiring highest accelerating gradient E acc or lowest surface resistance R S at temperatures of 2 K and below. The reason for this is that R S increases strongly with E acc . The origin of this field dependent surface resistance has been the subject of many past and recent studies [2][3][4][5], but is still far from being fully understood. The film thickness of about 1.5 µm is large compared to the London penetration depth λ L of about 32 nm. Differences in the performance (apart from thermal conductivity issues [6]) should therefore be correlated to the manufacturing procedure and the resulting surface structure. Since no single dominant source can be expected, several * Tobias.Junginger@helmholtz-berlin.de † TRIUMF Canada's National Laboratory for Particle and Nuclear Physics, Vancouver hypotheses need to be addressed individually to identify their origin and possibly mitigate their influence on the surface impedance and SRF cavity performances. A. Surface magnetism, a possible source of RF dissipationA possible source of dissipation under RF fields is surface magnetism in the oxide layer; magnetic impurities have a well known deleterious effect on superconductivity, causing inelastic scattering of the Cooper pairs [7] that increase the surface resistance R S and lower the quality factor Q ∝ 1/R S of superconducting RF cavities. The presence of localized magnetic moments on bulk niobium samples was revealed for the first time by Casalbuoni et al. in 2005 [8] by SQUID magnetometry. The AC magnetic susceptibility was measured in an external magnetic field of 0.7 T on Nb samples prepared with standard SRF cavity treatments, i.e. buffered chemical polishing (BCP), electropolishing (EP) and low temperature baking at about 120• C. In all cases, the samples displayed a Curie-Weiss behavior below 50 K indicativ...

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Section: Longitudinal Field Studies Of the Hipims Samplesupporting

confidence: 80%

“…The temperature dependence displayed in Fig. 11 significantly differs from what has been observed in [44] and therefore suggests an additional cause for the muon dynamics in addition to hopping, which might be indeed paramagnetic impurities as suggested from the zero field LE-µSR and the PCT studies.…”

Section: Longitudinal Field Studies Of the Hipims Samplementioning

confidence: 66%

A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

Junginger

Calatroni

Sublet

et al. 2017

Supercond. Sci. Technol.

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show abstract

“…Thus the one-phonon process is not relevant. We note that recent experiments 18 in very pure Nb also show too small a damping at low temperatures to be explained by incoherent processes only.…”

mentioning

confidence: 51%

Studies ofμ+Localization in Cu, Al, and Al Alloys in the Temperature Interval 0.03-100 K

et al. 1980

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“…Ниобий. Релаксации спина мюона в ниобии посвящено большое число работ [28,29,[35][36][37][38][39][40][41], Зависимость наблюдаемой скорости релаксации от концентрации и вида примесей позволила сделать вывод, что релаксация спина мюонов в ниобии (а также в ряде других исследованных металлов, кроме меди) обусловлена наличием ловушек [42]. Совре менные данные о величине для водорода в ниобии [3,4] полностью подтверждают этот вывод.…”

Section: анализ экспериментальных данныхunclassified

“…5. Зависимость скорости релаксации спина мюона от темпе ратуры в ниобии [37]. а -3700 ppm N, О, С. б -Менее 60 ррm N, О, С. в -10-20 ррm N, О, С Рис.…”

Section: анализ экспериментальных данныхunclassified

Muon spin relaxation in crystals with defects

Morozov¹,

Сигов²

1993

Usp. Fiz. Nauk

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Muon diffusion in niobium in the presence of traps

Cited by 27 publications

References 5 publications

A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

Studies ofμ+Localization in Cu, Al, and Al Alloys in the Temperature Interval 0.03-100 K

Muon spin relaxation in crystals with defects

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