Frequency Dependence of Superconducting Cavity <i>Q</i> and Magnetic Breakdown Field

Rabinowitz, Mario

doi:10.1063/1.1653827

Cited by 14 publications

(10 citation statements)

References 6 publications

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“…He predicts an exponential dependence of the surface resistance on the peak magnetic field, above the onset of flux penetration, which well describes the experimental data. The data also show that the onset of the Q drop in the TE mode is higher than in the TM mode and this is compatible with the hypothesis of delayed flux penetration by the higher frequency of the rf field [25].…”

Section: Discussionsupporting

confidence: 77%

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Measurement of the high-fieldQdrop in theTM010andTE011modes in a niobium cavity

Ciovati

Kneisel

2006

Phys. Rev. ST Accel. Beams

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In the last few years superconducting radio-frequency (rf) cavities made of high-purity (residual resistivity ratio > 200) niobium achieved accelerating gradients close to the theoretical limits. An obstacle towards achieving reproducibly higher fields is represented by ''anomalous'' losses causing a sharp degradation of the cavity quality factor when the peak surface magnetic field (B p ) is above about 90 mT, in the absence of field emission. This effect, called ''Q drop'' has been measured in many laboratories with single-and multicell cavities mainly in the gigahertz range. In addition, a lowtemperature (100 -140 C) ''in situ'' baking of the cavity was found to be beneficial in reducing the Q drop. In order to gain some understanding of the nature of these losses, a single-cell cavity has been tested in the TM 010 and TE 011 modes at 2 K. The feature of the TE 011 mode is to have zero electric field on the cavity surface, so that electric field effects can be excluded as a source for the Q drop. This article will present some of the experimental results for different cavity treatments and will compare them with existing models.

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Section: Discussionsupporting

confidence: 77%

“…Their size has been determined experimentally by ''trial and error'' and the orientation is such that the plane of the loop is parallel to the cavity equatorial plane. 25 C removing about 20 m of niobium from the inner cavity surface, after initial removal of about 130 m after the cavity fabrication;…”

Section: A Experimental Setupmentioning

confidence: 99%

Measurement of the high-fieldQdrop in theTM010andTE011modes in a niobium cavity

Ciovati

Kneisel

2006

Phys. Rev. ST Accel. Beams

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“…[21][22][23] The bell-shaped trend of sensitivity as a function of mean free path (Fig. 1) may be obtained even from the static contribution alone; 24 however, our preliminary theoretical results suggest that also the dynamic dissipation may lead to the same trend.…”

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confidence: 64%

Effect of interstitial impurities on the field dependent microwave surface resistance of niobium

Martinello

Grassellino

Checchin

et al. 2016

Applied Physics Letters

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Previous work has demonstrated that the radio frequency surface resistance of niobium resonators is dramatically reduced when nitrogen impurities are dissolved as interstitial in the material. This effect is attributed to the lowering of the Mattis-Bardeen surface resistance with increasing accelerating field; however, the microscopic origin of this phenomenon is poorly understood. Meanwhile, an enhancement of the sensitivity to trapped magnetic field is typically observed for such cavities. In this paper, we conduct a systematic study on these different components contributing to the total surface resistance as a function of different levels of dissolved nitrogen, in comparison with standard surface treatments for niobium resonators. Adding these results together, we are able to show which is the optimum surface treatment that maximizes the Q-factor of superconducting niobium resonators as a function of expected trapped magnetic field in the cavity walls. These results also provide insights on the physics behind the change in the field dependence of the Mattis-Bardeen surface resistance, and of the trapped magnetic vortex induced losses in superconducting niobium resonators.

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“…Here we consider trapped fields far below H c2 and, therefore, neglect the interaction between different fluxoids, which is a rapidly decreasing function of the interfluxoid spacing. We also do not include the time-dependent Lorentz force acting between the surface screening currents in the cavity and the trapped flux, as its net effect is the oscillation of the surface segments of the magnetic flux around the stable equilibrium position [21,23,24].…”

Section: Magnetic Flux Migrationmentioning

confidence: 99%

Quench-Induced Degradation of the Quality Factor in Superconducting Resonators

et al. 2016

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Quench of superconducting radio-frequency cavities frequently leads to the lowered quality factor Q 0 , which had been attributed to the additional trapped magnetic flux. Here we demonstrate that the origin of this magnetic flux is purely extrinsic to the cavity by showing no extra dissipation (unchanged Q 0 ) after quenching in zero magnetic field, which allows us to rule out intrinsic mechanisms of flux trapping such as generation of thermal currents or trapping of the rf field. We also show the clear relation of dissipation introduced by quenching to the orientation of the applied magnetic field and the possibility to fully recover the quality factor by requenching in the compensated field. We discover that for larger values of the ambient field, the Q-factor degradation may become irreversible by this technique, likely due to the outward flux migration beyond the normal zone opening during quench. Our findings are of special practical importance for accelerators based on low-and medium-β accelerating structures residing close to focusing magnets, as well as for all high-Q cavity-based accelerators.

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Frequency Dependence of Superconducting Cavity Q and Magnetic Breakdown Field

Cited by 14 publications

References 6 publications

Measurement of the high-fieldQdrop in theTM010andTE011modes in a niobium cavity

Measurement of the high-fieldQdrop in theTM010andTE011modes in a niobium cavity

Effect of interstitial impurities on the field dependent microwave surface resistance of niobium

Quench-Induced Degradation of the Quality Factor in Superconducting Resonators

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