Extension of the measurement capabilities of the quadrupole resonator

Junginger, Tobias; Weingarten, W.; Welsch, Carsten

doi:10.1063/1.4725521

Cited by 15 publications

(14 citation statements)

References 17 publications

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“…For a more detailed description of the QPR and of its working principle, in particular, of the calorimetric testing technique for superconducting samples, we refer to Refs. [17,18], and references therein.…”

Section: A the Quadrupole Resonatormentioning

confidence: 99%

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Cryogenic surface resistance of copper: Investigation of the impact of surface treatments for secondary electron yield reduction

Calatroni

Arzeo

Aull

et al. 2019

Phys. Rev. Accel. Beams

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The surface resistance of copper samples with an amorphous carbon (a-C) coating or with laser surface structuring, the surface treatments of choice for electron cloud suppression in critical cryogenic sectors of the high-luminosity upgrade of the Large Hadron Collider (HL-LHC), has been measured for the first time at a cryogenic temperature using the quadrupole resonator at CERN. Three different frequencies of relevance for evaluating beam impedance effects, namely, 400, 800, and 1200 MHz, have been investigated. No significant increase in surface resistance is observed for the a-C coating, compared to plain copper. In the case of laser structuring, the surface resistance depends on the direction of the surface currents relative to the laser-engraved groove pattern. The increase is minimal for parallel patterns, but in the perpendicular case the surface resistance increases considerably. Radio frequency (rf) heating from wake losses would then also increase in the HL-LHC case; however, the reduction in the power deposited onto the cold surfaces thanks to electron cloud suppression would still outweigh this effect.

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Section: A the Quadrupole Resonatormentioning

confidence: 99%

“…In this paper, we report on the measurement of the surface resistance of both a-C-coated and LESS-treated copper using the superconducting quadrupole resonator (QPR) [17,18]. We first describe the measurement system and the sample preparation, followed by the experimental results and their possible implications for the HL-LHC.…”

Section: Introductionmentioning

confidence: 99%

Cryogenic surface resistance of copper: Investigation of the impact of surface treatments for secondary electron yield reduction

Calatroni

Arzeo

Aull

et al. 2019

Phys. Rev. Accel. Beams

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“…The phenomenological fit parameters (also found in Tab. I) correspond to physical meaningful parameters (compare with [7] and quotations therein and [8], [9]) as β * =1, ε r =10, E c − E F =0.05 eV, ∆=1.18 meV, d=1.65 nm and xn T =6.7·10 15…”

Section: A Tesla Type Bulk Niobium Cavitymentioning

confidence: 98%

“…For the sample surface area of the Quadrupole Resonator this is not the case. By the calorimetric (RF-DC compensation) technique explained in detail in [15] one obtains the power dissipated under RF P RF directly. Using the field distribution on the sample and in the entire resonator volume one can derive the magnetic surface resistance R S of the sample using…”

Section: Quadrupole Resonator Measurementsmentioning

confidence: 99%

Experimental Evidence for Electric Surface Resistance in Niobium

Junginger

Aull

Weingarten³

et al. 2017

IEEE Trans. Appl. Supercond.

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Identifying the loss mechanisms of niobium cavities enables an accurate determination of applications for future accelerator projects and points to research topics required to mitigate current limitations. For several cavities an increasing surface resistance above a threshold field, saturating at higher field has been observed. Measurements on samples give evidence that this effect is caused by the surface electric field. The measured temperature and frequency dependence is consistent with a model that accounts for these losses by interface tunnel exchange between localized states in dielectric oxides and the adjacent superconductor.

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“…Hence, for R&D on materials, coatings or surface treatments aiming at application in SRF cavities, precision measurements of the surface resistance are required. The Quadrupole Resonator (QPR) is a dedicated sample-test cavity, providing high resolution measurements in a wide parameter space of temperature and RF field at three different frequencies [1][2][3][4] . With a first operating quadrupole mode at about 415 MHz, R BCS at 2 K is typically smaller than 2 nΩ, enabling direct measurements of R res .…”

Section: Introductionmentioning

confidence: 99%

Mitigation of parasitic losses in the quadrupole resonator enabling direct measurements of low residual resistances of SRF samples

Keckert

Kleindienst

Knobloch

et al. 2021

Preprint

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The quadrupole resonator (QPR) is a dedicated sample-test cavity for the RF characterization of superconducting samples in a wide temperature, RF field and frequency range. Its main purpose are high resolution measurements of the surface resistance with direct access to the residual resistance thanks to the low frequency of the first operating quadrupole mode. Besides the well-known high resolution of the QPR, a bias of measurement data towards higher values has been observed, especially at higher harmonic quadrupole modes. Numerical studies show that this can be explained by parasitic RF losses on the adapter flange used to mount samples into the QPR. Coating several micrometer of niobium on those surfaces of the stainless steel flange that are exposed to the RF fields significantly reduced this bias, enabling a direct measurement of a residual resistance smaller than 5 nΩ at 2 K and 413 MHz. A constant correction based on simulations was not feasible due to deviations from one measurement to another. However, this issue is resolved given these new results.

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Extension of the measurement capabilities of the quadrupole resonator

Cited by 15 publications

References 17 publications

Cryogenic surface resistance of copper: Investigation of the impact of surface treatments for secondary electron yield reduction

Cryogenic surface resistance of copper: Investigation of the impact of surface treatments for secondary electron yield reduction

Experimental Evidence for Electric Surface Resistance in Niobium

Mitigation of parasitic losses in the quadrupole resonator enabling direct measurements of low residual resistances of SRF samples

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