Optimum sensitivity of an externally shielded cryogenic current comparator

Early, M.D.; Jones, K. L.

doi:10.1109/19.571884

Cited by 17 publications

(16 citation statements)

References 4 publications

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“…The specifications to prevent the system against any large loss of sensitivity are well described in the literature. 12,13 In particular, the pick-up coil self-inductance has to be matched with the input inductance L SQ of the SQUID. As the selfinductance of this pick-up coil is completely screened by the superconducting torus, only the calculation of the effective self-inductance L CCC of the superconducting torus is required.…”

Section: B Coupling Between CCC and Squidmentioning

confidence: 99%

Ultralow noise current amplifier based on a cryogenic current comparator

Gay

Piquemal

Genevès

2000

Review of Scientific Instruments

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This article describes the development of a current amplifier operating at 4.2 K designed for very low current measurements. A cryogenic current comparator with a winding ratio of 10 000/1, a low noise dc superconducting quantum interference device, and a very efficient magnetic shield are combined to reach an equivalent input noise of 4 fA/√Hz in the signal bandwidth and a flicker noise corner around 0.5 Hz.

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Section: B Coupling Between CCC and Squidmentioning

confidence: 99%

Ultralow noise current amplifier based on a cryogenic current comparator

Gay

Piquemal

Genevès

2000

Review of Scientific Instruments

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“…A simplified calculation (with a claimed accuracy of about 20 %) for the sensitivity of an externally shielded CCC, recently published [4], made a substantial contribution. Nevertheless, using a standard, discrete, fast Fourier-transform method for calculating only the current distribution of the external open-ended cylindrical shield, this calculation was based on a number of approximations and still left some questions unanswered.…”

Section: Introductionmentioning

confidence: 99%

On forward estimate of the sensitivity of a cryogenic current comparator

Frantsuz

1998

Metrologia

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“…By solving the Fredholm integral equation we have obtained an analytic expression for the current distribution on the outer surface. These findings will be useful for the sensitivity analysis of an HTS CCC similar to those developed for a low-temperature superconducting CCC [12,13].…”

Section: Discussionmentioning

confidence: 92%

“…In that way, the effect of the cut can be screened by increasing the overlapping region, so that for large-enough overlap the SQUID detects only the magnetic field of the equilibrium supercurrents flowing on the outside surface of the shield [11]. Aspects of the LTS CCC design have been considered for example in [12] and [13].…”

Section: Introductionmentioning

confidence: 98%

Magnetic-field calculation for a high-temperature superconducting cryogenic current comparator

Bubanja¹

2006

J Eng Math

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The problem considered in this paper arises in the design of a high-temperature superconducting cryogenic current comparator (CCC). The CCC consists of two currents flowing in opposite directions inside a toroidal superconducting shield. The shield has a radial cut, necessary for the measurement of the current ratio, but causing an error in the obtained ratio. The problem of interest is the dependence of the error on the geometric parameters of the device: the major and minor radii of the shield, the cut width, the material thickness, and the location of the currents. In the first part of the paper, a toroidal shield with an infinitesimal cut is considered and analytic expressions are derived for the magnetic field and the surface-current distribution. In the second part, a cut of finite width is introduced. Since all the perturbing currents are present in the narrow region around the cut, a shield of cylindrical shape is assumed. Expressions are derived for the flux through the cut and the magnetic field around the cut. Analytical results are in good agreement with the numerical results obtained by a finite-element method. In the final part, the expression for the ratio error is derived, which shows that in order to minimize the error, currents should be concentrated around the shield axis, the major radius of the shield should be maximized and the bore radius minimized. The error depends logarithmically on the cut width.

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Optimum sensitivity of an externally shielded cryogenic current comparator

Cited by 17 publications

References 4 publications

Ultralow noise current amplifier based on a cryogenic current comparator

Ultralow noise current amplifier based on a cryogenic current comparator

On forward estimate of the sensitivity of a cryogenic current comparator

Magnetic-field calculation for a high-temperature superconducting cryogenic current comparator

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