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Al alloy-ceramic ultrahigh vacuum and cryogenic feedthrough useful from dc to 6.5 GHz
Classified
abstracts
5914-5922
diagnostic system of plasma fusion experiments is described. Special emphasis is given to the behaviour of such pumps under the specific conditions of these experiments. The impact of tritium and a radioactive environment and the presence of strong magnetic fields requires the use of selected materials within the pump. The necessary modifications of a standard turbomolecular pump are described in detail. Such a modified turbomolecular pump is capable of pumping tritium and withstand a radiation dose of 10’ rad. (West Germany) Dieter G Goetz, Vucuum, 32 (10/l l), 1982, 703-706. 21 5914. Experimental performance of an open structure cryopump. (GB) The Joint European Torus (JET) will utilize neutral injection as a form of additional heating. One important aspect of the neutral injector is the requirement of a large scale pumping system to handle c 250 torr I s- ’ of H, and D, gas with pumping speeds of up to 10’ I ss’. With existing technology, the only economical way to provide the necessary pumping speed is by means of liquid helium condensation cryopumps. A major problem in the design ofcryopumps is that of reducing thermal loading on the helium surfaces whilst maintaining adequate conductance for gas molecules. To achieve the required pumping speed within the space limitations of the JET injector, a ‘Serial Open Structure (Four Stage)’ pump has been designed and is at present being manufactured. The design aims to provide roughly twice the speed of the conventional chevron pump. The compact Open Structure concept, which also lends itself to ease of fabrication, has been checked experimentally on a single stage model cryopump (pumping speed for H, _ 60,000 I s i. In this paper we describe this experimental work, the results of which, together with theoretical design calculations, formed the design basis for the final JET Serial Open Structure. A relative comparison of pumping speed, thermal loading and also performance in the presence of an energetic particle beam (7 amps at 50 keV) has been made with a conventional chevron pump under identical test conditons. J R Coupland et al, Vacuum, 32 (10/l I), 1982, 613618. 22. GAUGES
AND MEASUREMENT
OF LOW PRESSURES
22 5915. Methods of pumping speed and gas release measurement in ionization gauge heads--A review. (GB) The problems associated with the change of both the equilibrium and composition of the residual gas within ionization gauge heads during measurements are presented. The phenomena which contribute to the specific shape of the plot (log P,t) are discussed in some detail as a basis for understanding the behavior of gauge heads as sinks and/or sources of gas. A critical analysis of the physical principles underlying the methods for the determination of a gas removed/or re-emitted is given. Understanding of the processes discussed will permit the selection of the most adequate method for the measurement of the pumping and gas release in an ionization gauge head during its operation. By using suitable experimental methods, accurate determination of these characteristics is possible. The results obtained can be used to correct the pressure readings taken with gauge heads in which ionized gas is used as a means of determining gas density. (Israel) A Berman, Vucuum, 32 (8) 1982, 497-508. 22 5916. Spinning rotor vacuum gauges. (GB) The decay of a freely rotating body immersed in a rarified gas can be used for quantitative determination of specific gas parameters such as molecular weight, rate of impingement, pressure, viscosity, etc. Instruments based upon this mechanism are described and discussed. Special attention is paid to measurement stability and accuracy which are particularly dependent on the geometrical structure and on the surface conditions of the rotating body. (Germany) J K Fremerey, Vacuum, 32 (IO/l I), 1982. 685690. 23. PLUMBING,
VACUUM
VALVES,
BAFFLES
AND TRAPS
5917. Guidelines for construction of low-pressure gas manifolds. (USAF5 Expressions are obtained for the outflow pattern from the orifices of a gas manifold in the molecular flow regime. The example considered in detail is a section oftubing with identical holes equally spaced along the tube. The manifold is characterized by k, the number of holes, and n, a conductance ratio. Example of outflow patterns for various values of n and k are given. The quantity kn- ‘I’ emerges as a figure of merit for uniform discharge. A simple experiment supports the usefulness of the model used. T C Paulick, J Vuc Sci Technol, 21 (4). 1982, 1032-1036.
23 5918. The effect of the inlet valve on the ultimate vacua above integrated pumping groups. (GB) The influence of the inlet valve on the ultimate vacua of integrated pumping groups, each consisting of a vapour pump, watercooled baffle and an inlet valve mounted in the same casing, is discussed. The difference in the mass spectra above the pumping groups when using various inlet valve lubricants are given. A quartz crystal microbalance is used to show the effect on system cleanliness of both the speed of operation of the inlet valve and the chamber pressure when the valve is operated. Awareness of the influence of these valve parameters on the ultimate vacuum and system cleanliness makes it possible to select the arrangement and operational mode that will give the best high vacuum performance. N T M Dennis et al, Vacuum, 32 (lO/il), 1982, 631633. 23 5919. Specimen manipulators for high resolution in ultra-high vacuum. (GB) A number of specimen manipulators have been designed for use in a variety of surface science studies including electron energy-loss scattering and atom scattering from surfaces. Provision is made for three orthogonal translations (X, Y, 2) as well as angular rotations about three independent axes. These high precision manipulators are suitable for use in an ultrahigh vacuum environment. Particular attention has been paid to the elimination of the stray magnetic fields that are normally encountered in such complex mechanisms. P V Head et al, Vacuum, 32 (lO/ll), 1982, 64644. 23 5920. Al alloy-ceramic ultrahigh vacuum and cryogenic feedthrough useful from dc to 6.5 GHz. (GB) A bakeable (150°C). Coolable (~2.17 K) SMA coaxial vacuum feedthrough is described. The VSWR is less than 1.5 from dc to 6.5 GHz. An aluminium alloy outer shield and ceramic insulator are brazed with aluminium alloy solder in a vacuum furnace. The feedthrough can be welded directly to an aluminium alloy flange with an electron beam.
(Japan) Hajime Ishimaru, 24. LEAK
Vacuum, 32 (12) 1982, 753-755.
DETECTORS
AND LEAK DETECTION
24 5921. problems in monitoring partial pressures in industrial vacuum plant. (GB) A simple pressure divider arrangement comprising calibrated conductances, quadrupole and total pressure monitors and a pump having a restricted orifice is described for use when sampling gases in industrial processes at pressures of up to I mbar. Preliminary results indicate that use of such a system presents many problems. The monitor system behaves inconsistently for water vapour, giving low readings by 25-50% and, for hydrocarbons. the results are completely unreliable. S Darling and J H Leek, Vacuum, 32 (3). 1982, 183-184.
III. Vacuum
applications
30. EVAPORATION
AND DEPOSITION
IN VACUO
30 5922. The electrical resistivity of thin metal films with unlike surfaces. (GB) The variation of the resistivity with thickness d and bulk electron mean free path i, of thin metal films with unlike surfaces is calculated using Soffer’s angularly dependent surface scattering model. Tabular values for the resistivity enhancement due to a range of surface roughness combinations are presented. It is shown that in the limit of one very smooth and one very rough surface, the effect, as expected, is simply an apparent doubling in the sample thickness. This contrasts with the much more likely situation of one relatively rough surface and one smooth surface. For this case it is shown that at high h’ values (~=d/,l.,) the dependence of the resistivity on K varies approximately as the rougher surface limit, while at low K values the variation approaches the limit of a sample ofdouble thickness having, on both surfaces, the higher roughness. The overall effect in this case is that the resistivity appears to vary in the manner expected from an intermediate value of surface roughness with a changed Q .E., value, p, being the bulk resistivity. It is demonstrated that only in the limit of identical surfaces, or one very smooth and one very rough surface, with in either case no, or at least known and quantifiable, grain boundary scattering, will the determination of p,l, values be meaningful. Consequently p =i, values determined in the past from the measurement of the variation with thickness of the resistivity of thin films are often substantially in error. J R Sambles and KC Elsom, J Phys D: Appl Phys, 15 (8), 1982,1459-1467. 329
abstracts
5914-5922
diagnostic system of plasma fusion experiments is described. Special emphasis is given to the behaviour of such pumps under the specific conditions of these experiments. The impact of tritium and a radioactive environment and the presence of strong magnetic fields requires the use of selected materials within the pump. The necessary modifications of a standard turbomolecular pump are described in detail. Such a modified turbomolecular pump is capable of pumping tritium and withstand a radiation dose of 10’ rad. (West Germany) Dieter G Goetz, Vucuum, 32 (10/l l), 1982, 703-706. 21 5914. Experimental performance of an open structure cryopump. (GB) The Joint European Torus (JET) will utilize neutral injection as a form of additional heating. One important aspect of the neutral injector is the requirement of a large scale pumping system to handle c 250 torr I s- ’ of H, and D, gas with pumping speeds of up to 10’ I ss’. With existing technology, the only economical way to provide the necessary pumping speed is by means of liquid helium condensation cryopumps. A major problem in the design ofcryopumps is that of reducing thermal loading on the helium surfaces whilst maintaining adequate conductance for gas molecules. To achieve the required pumping speed within the space limitations of the JET injector, a ‘Serial Open Structure (Four Stage)’ pump has been designed and is at present being manufactured. The design aims to provide roughly twice the speed of the conventional chevron pump. The compact Open Structure concept, which also lends itself to ease of fabrication, has been checked experimentally on a single stage model cryopump (pumping speed for H, _ 60,000 I s i. In this paper we describe this experimental work, the results of which, together with theoretical design calculations, formed the design basis for the final JET Serial Open Structure. A relative comparison of pumping speed, thermal loading and also performance in the presence of an energetic particle beam (7 amps at 50 keV) has been made with a conventional chevron pump under identical test conditons. J R Coupland et al, Vacuum, 32 (10/l I), 1982, 613618. 22. GAUGES
AND MEASUREMENT
OF LOW PRESSURES
22 5915. Methods of pumping speed and gas release measurement in ionization gauge heads--A review. (GB) The problems associated with the change of both the equilibrium and composition of the residual gas within ionization gauge heads during measurements are presented. The phenomena which contribute to the specific shape of the plot (log P,t) are discussed in some detail as a basis for understanding the behavior of gauge heads as sinks and/or sources of gas. A critical analysis of the physical principles underlying the methods for the determination of a gas removed/or re-emitted is given. Understanding of the processes discussed will permit the selection of the most adequate method for the measurement of the pumping and gas release in an ionization gauge head during its operation. By using suitable experimental methods, accurate determination of these characteristics is possible. The results obtained can be used to correct the pressure readings taken with gauge heads in which ionized gas is used as a means of determining gas density. (Israel) A Berman, Vucuum, 32 (8) 1982, 497-508. 22 5916. Spinning rotor vacuum gauges. (GB) The decay of a freely rotating body immersed in a rarified gas can be used for quantitative determination of specific gas parameters such as molecular weight, rate of impingement, pressure, viscosity, etc. Instruments based upon this mechanism are described and discussed. Special attention is paid to measurement stability and accuracy which are particularly dependent on the geometrical structure and on the surface conditions of the rotating body. (Germany) J K Fremerey, Vacuum, 32 (IO/l I), 1982. 685690. 23. PLUMBING,
VACUUM
VALVES,
BAFFLES
AND TRAPS
5917. Guidelines for construction of low-pressure gas manifolds. (USAF5 Expressions are obtained for the outflow pattern from the orifices of a gas manifold in the molecular flow regime. The example considered in detail is a section oftubing with identical holes equally spaced along the tube. The manifold is characterized by k, the number of holes, and n, a conductance ratio. Example of outflow patterns for various values of n and k are given. The quantity kn- ‘I’ emerges as a figure of merit for uniform discharge. A simple experiment supports the usefulness of the model used. T C Paulick, J Vuc Sci Technol, 21 (4). 1982, 1032-1036.
23 5918. The effect of the inlet valve on the ultimate vacua above integrated pumping groups. (GB) The influence of the inlet valve on the ultimate vacua of integrated pumping groups, each consisting of a vapour pump, watercooled baffle and an inlet valve mounted in the same casing, is discussed. The difference in the mass spectra above the pumping groups when using various inlet valve lubricants are given. A quartz crystal microbalance is used to show the effect on system cleanliness of both the speed of operation of the inlet valve and the chamber pressure when the valve is operated. Awareness of the influence of these valve parameters on the ultimate vacuum and system cleanliness makes it possible to select the arrangement and operational mode that will give the best high vacuum performance. N T M Dennis et al, Vacuum, 32 (lO/il), 1982, 631633. 23 5919. Specimen manipulators for high resolution in ultra-high vacuum. (GB) A number of specimen manipulators have been designed for use in a variety of surface science studies including electron energy-loss scattering and atom scattering from surfaces. Provision is made for three orthogonal translations (X, Y, 2) as well as angular rotations about three independent axes. These high precision manipulators are suitable for use in an ultrahigh vacuum environment. Particular attention has been paid to the elimination of the stray magnetic fields that are normally encountered in such complex mechanisms. P V Head et al, Vacuum, 32 (lO/ll), 1982, 64644. 23 5920. Al alloy-ceramic ultrahigh vacuum and cryogenic feedthrough useful from dc to 6.5 GHz. (GB) A bakeable (150°C). Coolable (~2.17 K) SMA coaxial vacuum feedthrough is described. The VSWR is less than 1.5 from dc to 6.5 GHz. An aluminium alloy outer shield and ceramic insulator are brazed with aluminium alloy solder in a vacuum furnace. The feedthrough can be welded directly to an aluminium alloy flange with an electron beam.
(Japan) Hajime Ishimaru, 24. LEAK
Vacuum, 32 (12) 1982, 753-755.
DETECTORS
AND LEAK DETECTION
24 5921. problems in monitoring partial pressures in industrial vacuum plant. (GB) A simple pressure divider arrangement comprising calibrated conductances, quadrupole and total pressure monitors and a pump having a restricted orifice is described for use when sampling gases in industrial processes at pressures of up to I mbar. Preliminary results indicate that use of such a system presents many problems. The monitor system behaves inconsistently for water vapour, giving low readings by 25-50% and, for hydrocarbons. the results are completely unreliable. S Darling and J H Leek, Vacuum, 32 (3). 1982, 183-184.
III. Vacuum
applications
30. EVAPORATION
AND DEPOSITION
IN VACUO
30 5922. The electrical resistivity of thin metal films with unlike surfaces. (GB) The variation of the resistivity with thickness d and bulk electron mean free path i, of thin metal films with unlike surfaces is calculated using Soffer’s angularly dependent surface scattering model. Tabular values for the resistivity enhancement due to a range of surface roughness combinations are presented. It is shown that in the limit of one very smooth and one very rough surface, the effect, as expected, is simply an apparent doubling in the sample thickness. This contrasts with the much more likely situation of one relatively rough surface and one smooth surface. For this case it is shown that at high h’ values (~=d/,l.,) the dependence of the resistivity on K varies approximately as the rougher surface limit, while at low K values the variation approaches the limit of a sample ofdouble thickness having, on both surfaces, the higher roughness. The overall effect in this case is that the resistivity appears to vary in the manner expected from an intermediate value of surface roughness with a changed Q .E., value, p, being the bulk resistivity. It is demonstrated that only in the limit of identical surfaces, or one very smooth and one very rough surface, with in either case no, or at least known and quantifiable, grain boundary scattering, will the determination of p,l, values be meaningful. Consequently p =i, values determined in the past from the measurement of the variation with thickness of the resistivity of thin films are often substantially in error. J R Sambles and KC Elsom, J Phys D: Appl Phys, 15 (8), 1982,1459-1467. 329