Performance assessment of condensation pumping

Chubb, JN

doi:10.1016/s0042-207x(96)90029-9

Cited by 6 publications

(5 citation statements)

References 4 publications

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“…This value agrees fairly well with other measurements we made at much higher incidence rates and up to much higher coverages by studying the reflection of molecules from liquid-helium-cooled surfaces (Chubb andPollard 1965, 1966).…”

Section: Sticking Coeficient Obsevcationssupporting

confidence: 91%

“…The performance characteristics of condensation pumping, in common with other surface absorption techniques, need to be expressed in terms of events occurring at the pumping surface (Chubb 1966)-the probability of incident molecules sticking to the surface (the sticking coefficient) and the probability of molecules already on the surface leaving (the desorption rate). From a knowledge of these performance features under various condensation conditions, the pumping effect of any geometry of extended condensing surface in any defined vacuum system may be predicted by the Monte Carlo technique of analysing free molecular gas flow (Chubb 1965).…”

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

“…From a knowledge of these performance features under various condensation conditions, the pumping effect of any geometry of extended condensing surface in any defined vacuum system may be predicted by the Monte Carlo technique of analysing free molecular gas flow (Chubb 1965).…”

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

“…This can conveniently be done by the Monte Carlo technique of studying free molecular gas flow. The Monte Carlo program we have developed (Chubb 1965) allows direct calculation at any chosen position in the vacuum structure of the rate of incidence of molecules per molecule introduced into the system for chosen values of sticking coefficient at the condensing surface. A graph can then be constructed, as shown in figure 2, relating the impact probability, at chosen ion gauge or mass spectrometer locations, to the sticking coefficient.…”

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

“…A gas flow rate of 3 x 1014 molecules s-1 could be injected into the 60 1. volume of the chamber for times down to about 0-5 s to provide calibrating gas densities down to about 3 x lo9 molecules cm-3 (equivalent to about 100 ntorr). The use of the same gas flow system for calibration as for the condensation studies made the measurements of sticking coefficients independent of the absolute calibration of the gauges and mass spectrometers, and also independent of the absolute value of the gas flow rate (Chubb 1966).…”

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

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Vertical Coherence Measurements of Ambient Noise in Shallow Water off the East Coast of Korea

Cho¹,

Choi²

2011

Jpn. J. Appl. Phys.

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The condensation of hydrogen and deuterium on to liquid-helium-cooled surfaces is being studied for high-efficiency contamination-free pumping applications in plasma physics experiments.The present experimental studies show that the sticking coefficient of hydrogen and deuterium at room temperature increases during initial coverage of a liquid-heliumcooled condensing surface from around 0.5 at about 1013 molecules cm-2 to between 0.7 and 0.95 at 1016 molecules cm-2, and then remains essentially independent of further coverage. The sticking coefficient tends to increase with increasing gas incidence rate, but is only susceptible to surface temperature at the higher end of the range 2.1-3.7"~ for very low gas inflow rates.During initial coverage of the condensing surface the desorption rate of gas molecules increases with surface coverage and reaches a steady value for coverages of about 3 x 1016 molecules cm-2. This desorption rate does not decrease as rapidly with surface temperature as expected from published hydrogen and deuterium vapourpressure curves. Experiments show that this is due to thermal-radiation desorption effects. The application of condensation pumping in practice to maintain gas densities below about 5 x 108 molecules cm-3 (about 10 ntorr) thus requires some restriction of the thermal-radiation loading at the condensing surface.

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Section: Sticking Coeficient Obsevcationssupporting

confidence: 91%

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

Section: Experimental Techniques Of Performance Assessmentmentioning

confidence: 99%

See 3 more Smart Citations

Vertical Coherence Measurements of Ambient Noise in Shallow Water off the East Coast of Korea

Cho¹,

Choi²

2011

Jpn. J. Appl. Phys.

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Experience with a pulsed gas flow technique for calibrating vacuum gauges

Chubb

Gowland

1967

Vacuum

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Study of Some of the Parameters Affecting Knudsen Effusion. VI. Monte Carlo Analyses of Channel Orifices

Ward

Fraser

1969

The Journal of Chemical Physics

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Techniques for Monte Carlo simulation of real particle behavior have been extended to study the performance of channel orifices. Transmission coefficient calculations and wall-flux gradient behavior are considered. For the particular case L / R = 4.0, functions are derived to allow for variable orifice-to-collimator distances when the target collection method is used. A “state-of-the-art” discussion on orifice behavior is included to help delineate the purposes of this study. It is concluded that use of both knife-edged and channel orifices is sometimes necessary to establish the cell-orifice behavior of some systems; information derived from experimental studies, and from Monte Carlo analysis of flux relationships appropriate to the geometry of the system, seems to indicate that the channel orifice is a better choice for most effusion work.

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Performance assessment of condensation pumping

Cited by 6 publications

References 4 publications

Vertical Coherence Measurements of Ambient Noise in Shallow Water off the East Coast of Korea

Vertical Coherence Measurements of Ambient Noise in Shallow Water off the East Coast of Korea

Experience with a pulsed gas flow technique for calibrating vacuum gauges

Study of Some of the Parameters Affecting Knudsen Effusion. VI. Monte Carlo Analyses of Channel Orifices

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