Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>T</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math>

Huang, Shijie; Kubo, Takayuki; Geng, Rongli

doi:10.1103/physrevaccelbeams.19.082001

Cited by 42 publications

(32 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The surface resistance depends on the amplitude H 0 of the RF magnetic field H(t) = H 0 sin ωt and can be significantly altered by the materials treatments. For instance, R s of electropolished Nb cavities 4 at 2 K and 1 GHz increases with the RF field amplitude, consistent with the well-known reduction of a quasiparticle gap and the superfluid density by the RF pairbreaking currents [9][10][11] , grain boundaries and nonsuperconducting precipitates 5 , or trapped vortices [12][13][14][15][16][17][18][19] . However, the Nb cavities doped with nitrogen [20][21][22][23] , titanium 24 or other impurities 25,26 can exhibit a striking reduction of R s (H 0 ) by factors of 2-4 as H 0 increases from 0 to 0.5H c , where H c is the thermodynamic critical field.…”

Section: Introductionsupporting

confidence: 72%

“…If a magnetic field is applied, Abrikosov vortices can penetrate into the sample and modify the local density of states. Hot spots resulting from vortex bundles, trapped during the cavity cooldown through the superconducting critical T c , can essentially limit the performance of SRF cavities [12][13][14][15][16][17][18][19] . Imaging of trapped vortices can give valuable information about the electronic structure of the vortex core in the first few nm at the surface, which plays the key role in RF dissipation.…”

Section: Vorticesmentioning

confidence: 99%

See 1 more Smart Citation

Electron Tunneling and X-Ray Photoelectron Spectroscopy Studies of the Superconducting Properties of Nitrogen-Doped Niobium Resonator Cavities

et al. 2020

View full text Add to dashboard Cite

Scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to investigate the differences between the surface electronic structures and chemical structure of typically prepared and N-doped Nb cutouts from superconducting radio frequency (SRF) cavities. The goal of this work is to get insights into the fundamental physics and materials mechanisms behind the striking decrease of the surface resistance with the radiofrequency magnetic field, which has been observed by many groups on N-doped Nb cavities. In particular, we address the effects of N-doping on the superconducting properties at the surface of SRF cavities. XPS measurements reveal a significantly more oxidized Nb 3d states on the N-doped Nb surfaces which is confirmed by tunneling spectroscopy measurements. Analysis of the tunneling spectra in the framework of a recent model (A. Gurevich and T. Kubo Phys. Rev. B 96, 184515 ( 2017)) shows that the N-doping greatly reduces local distribution of superconducting properties on the surface, causes a significant shrinkage of the metallic suboxide and changes the contact resistance between the metallic suboxide and the bulk niobium toward an optimum value, resulting in a lower surface resistance. Combination of these factors enables one to effectively tune the density of states at the surface and to reveal the decrease of the surface resistance with the radio frequency field which follows from the BCS theory. A slightly reduced average gap and a smaller coherence length, revealed by tunneling spectroscopy in the vortex cores, have been found in the N-doped Nb samples compared to typically prepared Nb samples, indicating a stronger impurity scattering caused by nitrogen doping in a moderately disordered material.

show abstract

Section: Introductionsupporting

confidence: 72%

Section: Vorticesmentioning

confidence: 99%

Electron Tunneling and X-Ray Photoelectron Spectroscopy Studies of the Superconducting Properties of Nitrogen-Doped Niobium Resonator Cavities

et al. 2020

View full text Add to dashboard Cite

show abstract

“…However, there are still significant variations in flux trapping and flux expulsion from Nb cavities that are not well understood, for instance, cavities manufactured from Nb sheet with same material specifications produced by the same vendor, and treated by the same recipe produces cavities that expel flux differently 2 . The increase in residual resistance due to the trapped magnetic field has been studied in several SRF cavities with respect to the starting Nb material 24 , surface preparation 18 , and nitrogen diffusion conditions 25 . Theoretically, a multi-scale collective pinning mechanism is suggested for rf dissipation in SRF cavities 26 , and a recent review indicates pinning possibilities could be related to dislocation structures 27 .…”

Section: Introductionmentioning

confidence: 99%

Direct evidence of microstructure dependence of magnetic flux trapping in niobium

Balachandran¹,

Polyanskii²,

Chetri³

et al. 2021

Sci Rep

View full text Add to dashboard Cite

Elemental type-II superconducting niobium is the material of choice for superconducting radiofrequency cavities used in modern particle accelerators, light sources, detectors, sensors, and quantum computing architecture. An essential challenge to increasing energy efficiency in rf applications is the power dissipation due to residual magnetic field that is trapped during the cool down process due to incomplete magnetic field expulsion. New SRF cavity processing recipes that use surface doping techniques have significantly increased their cryogenic efficiency. However, the performance of SRF Nb accelerators still shows vulnerability to a trapped magnetic field. In this manuscript, we report the observation of a direct link between flux trapping and incomplete flux expulsion with spatial variations in microstructure within the niobium. Fine-grain recrystallized microstructure with an average grain size of 10–50 µm leads to flux trapping even with a lack of dislocation structures in grain interiors. Larger grain sizes beyond 100–400 µm do not lead to preferential flux trapping, as observed directly by magneto-optical imaging. While local magnetic flux variations imaged by magneto-optics provide clarity on a microstructure level, bulk variations are also indicated by variations in pinning force curves with sequential heat treatment studies. The key results indicate that complete control of the niobium microstructure will help produce higher performance superconducting resonators with reduced rf losses1 related to the magnetic flux trapping.

show abstract

“…Reduction of R s (or improvement of Q) has been the primary interest of researchers of resonant cavities over the last decades. Vortex-free Nb cavities [50][51][52][53][54][55] exhibit huge quality factor Q ∼ 10 10 -10 12 at T < 2 K [56][57][58][59] even under the strong rf current [60][61][62][63] close to the depairing current density. The depairing current density J d is related to the bias current of SSPD and is the maximum current that SRF cavities and superconducting cables can support.…”

Section: Introductionmentioning

confidence: 99%

Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor and depairing current density

Kubo

2021

Preprint

Self Cite

View full text Add to dashboard Cite

We investigate how a combination of a nonmagnetic-impurity scattering rate γ and finite subgap states parametrized by Dynes Γ affects various physical quantities relevant to to superconducting devices: kinetic inductance L k , complex conductivity σ, surface resistance Rs, quality factor Q, and depairing current density J d . All the calculations are based on the Eilenberger formalism of the BCS theory. We assume the device materials are extreme type-II s-wave superconductors. It is well known that the optimum impurity concentration (γ/∆0 ∼ 1) minimizes Rs. Here, ∆0 is the pair potential for the idealized (Γ → 0) superconductor for the temperature T → 0. We find the optimum Γ can also reduce Rs by one order of magnitude for a clean superconductor (γ/∆0 < 1) and a few tens % for a dirty superconductor (γ/∆0 > 1). Also, we find a nearly-ideal (Γ/∆0 ≪ 1) clean-limit superconductor exhibits a frequency-independent Rs for a broad range of frequency ω, which can significantly improve Q of a very compact cavity with a few tens of GHz frequency. As Γ or γ increases, the plateau disappears, and Rs obeys the ω 2 dependence. The subgap-state-induced residual surface resistance Rres is also studied, which can be detected by an SRF-grade high-Q 3D resonator. We calculate L k (γ, Γ, T ) and J d (γ, Γ, T ), which are monotonic increasing and decreasing functions of (γ, Γ, T ), respectively. Measurements of (γ, Γ) of device materials can give helpful information on engineering (γ, Γ) via materials processing, by which it would be possible to improve Q, engineer L k , and ameliorate J d .

show abstract

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown throughTc

Cited by 42 publications

References 21 publications

Electron Tunneling and X-Ray Photoelectron Spectroscopy Studies of the Superconducting Properties of Nitrogen-Doped Niobium Resonator Cavities

Electron Tunneling and X-Ray Photoelectron Spectroscopy Studies of the Superconducting Properties of Nitrogen-Doped Niobium Resonator Cavities

Direct evidence of microstructure dependence of magnetic flux trapping in niobium

Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor and depairing current density

Contact Info

Product

Resources

About