Evidence for non-linear BCS resistance in SRF cavities

Bauer, P.; Solyak, N.; Ciovati, Gianluigi; Eremeev, Grigory; Gurevich, A.; Lilje, L.; Visentin, B.

doi:10.1016/j.physc.2006.03.056

Cited by 28 publications

(25 citation statements)

References 3 publications

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“…Fortunately, to estimate its magnitude under different conditions, we can use ∆T out (B rf ) = T out − T b directly measured on the outside cavity walls by temperature mapping [32]. Given the surface magnetic field H and the average surface resistance R s = G/Q 0 from rf measurements, and the outside wall temperature T out from temperature mapping (taking into account thermometers efficiency [32] of ∼ 35%), we apply a 1D heat diffusion model with a surface heat source of P = 1/2R s H 2 , and niobium thermal conductivity κ(T ) = 0.7e 1.65T −0.1T 2 W/m·K [33] to calculate the rf surface temperature T rf . An expected increase in R BCS due to heating is then calculated and the results at T = 2 K and T = 1.66 K are shown in Fig.…”

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confidence: 99%

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

Romanenko

2013

Applied Physics Letters

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Utilizing difference in temperature dependencies we decoupled BCS and residual components of the microwave surface resistance of superconducting niobium at all rf fields up to B rf ∼ 110 mT.We reveal that the residual resistance decreases with field at B rf < ∼ 40 mT and strongly increases in chemically treated niobium at B rf > 80 mT. We find that BCS surface resistance is weakly dependent on field in the clean limit, whereas a strong and peculiar field dependence emerges after 120 • C vacuum baking.

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confidence: 99%

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

Romanenko

2013

Applied Physics Letters

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“…The reduction of the mean free path by baking indicates that the surface resistance changes from clean (l > ) to dirty (l < ) limit and therefore the development of a theoretical treatment of the BCS surface resistance at low temperature (T=T c < 0:23) and high rf field (B rf =B c > 0:5) as a function of the mean free path could be very useful, as already pointed out in Ref. [4].…”

Section: Comparison Of Modelsmentioning

confidence: 85%

“…Postpurification of the niobium cavity improves the thermal conductivity of the material, which should reduce the Q drop if it would be caused by the limited heat transfer from the rf surface to the helium bath, as proposed by the so-called thermal feedback model described in Ref. [4].…”

Section: Introductionmentioning

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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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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“…The R s (B p ) dependence predicted by the thermal feedback model is not as strong as is often measured experimentally, particularly for cavities at gigahertz frequency for which R BCS is relatively low compared to S-band cavities [121]. The convenient availability of large Nb crystals has enabled a more precise characterization of the Kapitza resistance at the niobium/superfluid helium interface [128].…”

Section: Medium-field Q-slopementioning

confidence: 93%

Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications

Reece¹,

Ciovati²

2013

Reviews of Accelerator Science and Technology

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Superconducting rf technology (SRF) is evolving rapidly as are its applications. While there is active exploitation of what one may term the current state-of-the-practice, there is also rapid progress expanding in several dimensions the accessible and useful parameter space. While state-of-the-art performance sometimes outpaces thorough understanding, the improving scientific understanding from active SRF research is clarifying routes to obtain optimum performance from present materials and opening avenues beyond the standard bulk niobium. The improving technical basis understanding is enabling process engineering to both improve performance confidence and reliability and also unit implementation costs. Increasing confidence in the technology enables the engineering of new creative application designs. We attempt to survey this landscape to highlight the potential for future accelerator applications.

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Evidence for non-linear BCS resistance in SRF cavities

Cited by 28 publications

References 3 publications

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

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

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

Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications

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