Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

Romanenko, Alexander

doi:10.1063/1.4812665

Cited by 35 publications

(37 citation statements)

References 43 publications

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“…Thus, niobium after the surface treatments exhibits similar defect depth distribution as other metals studied, nevertheless high surface sensitivity to the positron annihilation is a new feature of this metal. This was also observed by Romanenko and Grassellino who measured the microwave surface resistivity of superconducting niobium at RF field [30]. This resistivity strongly increases in chemically treated niobium, presumably due to different roughness.…”

Section: Remarkssupporting

confidence: 79%

Positron Annihilation Studies of the Near-Surface Regions of Niobium before and after Wear Treatment

Dryzek

Horodek

2017

Tribol Lett

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The positron annihilation studies of well-annealed niobium samples after dry sliding or sandblasting are reported. These treatments modify surface and subsurface regions introducing crystalline defects, which are extended beneath the surface of the sample at a depth of about 140 lm for the highest applied load of 50 N. These defects can be identified as dislocations with jogs or vacancies near dislocations. The obtained depth profile of mean positron lifetime reflects the defect depth distribution and exhibits the characteristic plateau near the worn surface, which disappears when lowering of the applied load. A similar depth profile was obtained also for niobium samples after sandblasting. Slow positron beam studies revealed that at the surface of the samples after dry sliding or other treatments some defects that localize positrons are present. Additionally, a large value of positron diffusion length of about 266(33) nm was found for well annealed niobium.

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Section: Remarkssupporting

confidence: 79%

Positron Annihilation Studies of the Near-Surface Regions of Niobium before and after Wear Treatment

Dryzek

Horodek

2017

Tribol Lett

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“…It also plays a role in a systematic improvement of Q at mid and high field, as it is clear from figure 4 and 5. The origin of the improvement in Q stems from both an improvement in residual and BCS surface resistance, as a function of field, as it will be shown from the analysis of the decomposition [6] in the two components as a function of RF field, in figure 6. Fig.4 Effect of nitrogen infusion at 120°C versus standard 120°C bake post oxidation.…”

Section: Fig3mentioning

confidence: 95%

Unprecedented quality factors at accelerating gradients up to 45 MVm⁻¹in niobium superconducting resonators via low temperature nitrogen infusion

Grassellino

Romanenko

Trenikhina

et al. 2017

Supercond. Sci. Technol.

143

125

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We report the finding of new surface treatments that permit to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis-Bardeen surface resistance and residual resistance accordingly. In particular, we find surface "infusion" conditions that systematically a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art surface processing. Cavities subject to the new surface process have larger than two times the state of the art Q at 2K for accelerating fields > 35 MV/m. Moreover, very high accelerating gradients ~ 45 MV/m are repeatedly reached, which correspond to peak magnetic surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity surface.

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“…All of the other cavities out of our large set prepared with different surface treatments (see Table I) exhibited very similar Q saturation behavior at low fields. The drop in Q at higher fields of > ∼ 3 MV/m is due to so-called medium and high field Q slopes [1,9]; non-equilibrium quasiparticle energy distribution driven by the rf field is another possible contributor [29].…”

Section: Time (S)mentioning

confidence: 99%

Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes

Romanenko¹,

Schuster²

2017

Phys. Rev. Lett.

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In niobium superconducting radio frequency (SRF) cavities for particle acceleration, a decrease of the quality factor at lower fields-a so-called low field Q slope or LFQS-has been a long-standing unexplained effect. By extending the high Q measurement techniques to ultralow fields, we discover two previously unknown features of the effect: (i) saturation at rf fields lower than E_{acc}∼0.1 MV/m; (ii) strong degradation enhancement by growing thicker niobium pentoxide. Our findings suggest that the LFQS may be caused by the two level systems in the natural niobium oxide on the inner cavity surface, thereby identifying a new source of residual resistance and providing guidance for potential nonaccelerator low-field applications of SRF cavities.

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Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

Cited by 35 publications

References 43 publications

Positron Annihilation Studies of the Near-Surface Regions of Niobium before and after Wear Treatment

Positron Annihilation Studies of the Near-Surface Regions of Niobium before and after Wear Treatment

Unprecedented quality factors at accelerating gradients up to 45 MVm⁻¹in niobium superconducting resonators via low temperature nitrogen infusion

Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes

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Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

Cited by 35 publications

References 43 publications

Positron Annihilation Studies of the Near-Surface Regions of Niobium before and after Wear Treatment

Positron Annihilation Studies of the Near-Surface Regions of Niobium before and after Wear Treatment

Unprecedented quality factors at accelerating gradients up to 45 MVm−1in niobium superconducting resonators via low temperature nitrogen infusion

Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes

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Unprecedented quality factors at accelerating gradients up to 45 MVm⁻¹in niobium superconducting resonators via low temperature nitrogen infusion