A rotatable cryogenic target for use with molecular beams

Bentley, P.D.; Hands, B.A.

doi:10.1088/0022-3735/6/9/015

Cited by 3 publications

(4 citation statements)

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“…The highest resolution kernel in figure 11, with σ x = 0.7 mm, was achieved with bare 0.2 mm diameter type K wire scanned in MSLs dual heat-pipe scanner [26]. The lowest resolution kernel, with σ x = 28.5 mm, was achieved using a type S thermocouple in 4 mm twin-bore alumina in a furnace [45]. Also marked on figure 11(b) and listed in table 2 are the points in the responses corresponding to the frequency 1/(2πσ x ), which is suggested as a measure of the bandwidth by the equality of (10).…”

Section: Performance Of Real Scannersmentioning

confidence: 98%

“…Media with a high heat capacity and a high thermal conductivity are best. The dual heat-pipe scanner at MSL, which exploits a change of state by using direct immersion into the vapour space of a heat pipe [20,26], is superior to direct immersion in liquids such as water, oil or salt [11,15,25], which is, in turn, better than air-coupled scanning systems employing furnaces [45], fixed points [46], and thermowells [18,24]. Air coupling is usually required for the low-temperature zone, and made better with the use of forced air convection to improve the thermal contact with the air.…”

Section: Factors Affecting Resolutionmentioning

confidence: 99%

“…Figure 8 shows the frequency response for a range of beta pdfs with a constant spatial resolution, σ x , but varying symmetry. The curvature components α and β were chosen to be representative of the values calculated in section 4.5 [11] 2.9 2.4 70 3.8 0.0418 Tamba [18] 446 768 160 18.1 0.0088 Bentley [24] 81 787 250 19.0 0.0084 Bentley [45] 1412 217 450 28.5 0.0056 from least-squares fits of measured kernels. For comparison purposes, a Gaussian pdf having the same resolution is also plotted.…”

Section: Kernel Symmetrymentioning

confidence: 99%

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Thermocouple homogeneity scanning

Webster

White

2015

Metrologia

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The inhomogeneities within a thermocouple influence the measured temperature and contribute the largest component to uncertainty. Currently there is no accepted best practice for measuring the inhomogeneities or for forecasting their effects on real-world measurements. The aim of this paper is to provide guidance on the design and performance assessment of thermocouple inhomogeneity scanners by characterizing the qualitative performance of the various designs reported in the literature, and developing a quantitative measure of scanner resolution. Numerical simulations incorporating Fourier transforms and convolutions are used to gauge the levels of attenuation and distortion present in single-and double-gradient scanners. Single-gradient scanners are found to be far superior to double-gradient scanners, which are unsuitable for quantitative measurements due to their blindness to inhomogeneities at many spatial frequencies and severe attenuation of signals at other frequencies. It is recommended that the standard deviation of the temperature gradient within the scanner is used as a measure of the scanner resolution and spatial bandwidth. Recommendations for the design of scanners are presented, and include advice on the basic design of scanners, the media employed, operating temperature, scan rates, construction of survey probes, data processing, gradient symmetry, and the spatial resolution required for research and calibration applications.

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Section: Performance Of Real Scannersmentioning

confidence: 98%

Section: Factors Affecting Resolutionmentioning

confidence: 99%

Section: Kernel Symmetrymentioning

confidence: 99%

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Thermocouple homogeneity scanning

Webster

White

2015

Metrologia

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“…The apparatus, full details of which are available elsewhere (Hands & Bentley 1977;Bentley 1974), is shown schematically in figure 1. An aerodynamic molecular beam source was used in preference to an effusive source not only because the resulting beam is more nearly monoenergetic, but also because much higher intensi ties can be obtained.…”

Section: Introductionmentioning

confidence: 99%

The condensation of atmospheric gases on cold surfaces

Bentley

Hands

1978

Proc. R. Soc. Lond. A

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Data for the deposition of argon, nitrogen and carbon dioxide on cold, metal surfaces are considered in detail. It is concluded that argon and nitrogen deposit when the incident gas pressure equals the sublimation pressure at the respective surface temperature, and growth therefore proceeds without any significant intermediate nucleation barrier. Carbon dioxide, however, requires considerable supersaturation of the gaseous phase and consequently bulk deposition is inhibited by a nucleation barrier. The results are analysed with a view to determining the critical nucleus size and the adsorption energy. The ‘classical’ method of analysis gives unsatisfactory and inconclusive results. In contrast, the ‘atomistic’ approach is found to give a good account of the critical deposition phenomenon. The onset of gross deposition is found to be due entirely to capture of single molecules by stable nuclei, rather than by the formation of critical nuclei as the ‘ classical ’ theory wrongly assumes. The number of molecules in the critical nucleus is found to be about nine and a value of 9.4 kJ mol -1 is obtained for the adsorption energy, suggesting that nucleation occurs on top of a strongly bound adsorbed layer of contaminants or carbon dioxide itself, rather than on bare metal.

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The use of printed circuits in cryogenics as heat sinks for electrical temperature sensor leads

Bentley

Wooster

1977

Cryogenics

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A rotatable cryogenic target for use with molecular beams

Cited by 3 publications

References 0 publications

Thermocouple homogeneity scanning

Thermocouple homogeneity scanning

The condensation of atmospheric gases on cold surfaces

The use of printed circuits in cryogenics as heat sinks for electrical temperature sensor leads

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