- Email: [email protected]
20. Pumping systems
Classified
abstracts
537-547
the major reaction products observed. A comparison of experimental cross sections and corresponding rate constants for thermal-energy ions is made with theory. Measurements of the kinetic energy distributions of the ionic reaction products are also reported. T F Moran and L Friedman, J Chem Phys, 45 (IO), 15th Nov 1966, 3837-3845. 18 ~37 537. Electrical explosion of wires in air and in vacua. (USSR) Experiments on the explosion of copper wires by an electric current in air and in vacua are described. The current was obtained from a condenser battery yielding a 150 A discharge lasting for 40 ,ccsec. The copper sample, 85 mm long and 0.3 mm in diameter, was clamped in a stainless-steel cylinder provided with observation windows and evacuated to 2r 10-j torr. The nature of the explosion produced in the vacuum chamber was essentially different from explosions produced in air; evidence of this included spectroscopic records of the plasma associated with the explosions and the form of the respective volt/ampere characteristics. E K Chekalin and V S Shumanov, Book, “Research in Physical Gus Dynamics”, Moscow, 1966, 109, (in Russian). 18 538. The role of the material composing the central part of the cathode in a Penning-type discharge. (USSR) The role of the cathode material in determining the discharge current, over-all efficiency, and other parameters of Penning-type discharges is discussed. Since the state of the electrode surfaces changes rapidly in low-pressure discharges, particular attention must be paid to the reproducibility of the conditions when studying discharge parameters -failure to observe this has led to discrepancies in earlier-published data. New equipment ensuring reproducible conditions for Penningtype discharges at pressures of lo-” to lo-” torr is described. The material composing the central part of the cathode has a particularly severe effect on the discharge current when high-energy ions are passing along the axis. This effect increases as the work function of the cathode material falls. E M Reikhrudel’ et al, Radiotekh Elekfrotr, 11, ( I!) 1966, 2095-2098, (in Russian). 18 539. Instabilities in Penning discharges. (USA) Generation of electromagnetic energy in the microwave region in a cold-cathode Penning discharge at air pressures of 1 to 10 microns was studied using aluminium and graphite cathodes. B Agdur and U Ternstrom, Phys Rev Letters 13, 1965, 5-7. I8 540. First-order coupled wave equations for propagation in stratified compressible plasmas. (Australia) This paper deals with wave propagation in planar stratified, continuously varying, compressible, non-magnetized electron plasmas. The waves are coupled electromagnetic and electron acoustic waves, and are described by Maxwell’s equations coupled to the linearized single-fluid equations of hydrodynamics. Some first-order coupled wave equations are obtained and are transformed into convenient forms. Coupling, power flow, and approximate solutions are then discussed. (Authors). R Burman, Aus J Phys, 19, 1966, 747-757. 18 541. Non-equilibrium ionization growth in molecular hydrogen. (Australia) A thin-film cathode is used in an examination of the spatial growth of ionization in molecular hydrogen at high values of the parameter E/p (E is the electric field strength in V/cm, p is the gas pressure in torr at 0°C). Particular attention is given to the region of small gap separations d where non-equilibrium ionization growth occurs. The effect of non-uniformity of the electric field in this region due to anode perforations is demonstrated and the consequences of including ionization current measurements at small values of d in analyses of growth of current measurements are discussed. The variation of the “effective” Townsend coefficient a/p with E/p in uniform field conditions is obtained for values of E/p up to 1000 V crn~’ torr’. (Authors). S C Haydon and H M P Stock, Aus J Phys, 19, 1966, 795-803. I8 542. Electron drift and diffusion in deuterium at 293 K. (Australia) The drift velocity and the ratio of diffusion coefficient to mobility have been measured for electrons in deuterium at 293;K over the
188
ranges 0.006
respectively. (Authors).
The
18 543. Interaction of thermal electronics with polar molecules. (Austrdiia) Drift velocities of thermal electron swarms have been measured in pure ethylene gas and in mixtures of acetone, ethanolamine, ethylene diamine, ethanol, n-propanol, iso-propanol, chlorobenzene, dethyl ether, diethylamine, and propane with ethylene in a parallel plate ionization chamber evacuated by a 2 inch diameter silicone oil diffusion pump and rotary backing pumps to approximately IO-” torr. Cross sections for momentum transfer from electron to polar molecule deduced from these experiments and the literature arc compared with published “point dipole” theories. N Hamilton and J A D Stockdale, Arts J P/I_I,.s,19, 1966. 8 13-822. 18 544. Dependence of gas discharge maintaining voltage on the interelectrode distance. (USSR) Volt-centimeter characteristics of a gas discharge at ditrerent currents were investigated. The gas used was argon, and both electrodes were made from molybdenum. It is shown that for smaller currents the characteristics were displaced to the left side (to smaller critical distances). For interelectrode gaps larger than the critical distance, negative resistance with volt-ampere characteristics similar to those for subnormal glow discharge, but with far higher currents, may play a part. The possibility of the use of this negative resistance regime is briefly discussed and some recommendations to discharge tube designers are given. A E Ayzentson and N G Kashnikov, Zh Trkh Fiz. 36 ( I I), Nov 1966. 205 I -2055 (in Rnxsirrn).
II.
Vacuum
20. PUMPING
apparatus
and auxiliaries
SYSTEMS
20 : 34 Vacuum capabilities of the 150 cubic foot space facility at the Langley Research Centre. See abstract number 651. 20 545. Technology of vacuum equipment manufacture. (USSR) The conditions required for satisfactory operation of high-vacuum equipment are discussed and aspects of vacuum hygiene necessary for their fulfilment are considered. The types of materials best suited to vacuum work are discussed in relation to their gas-tightness and gas evolution under vacuum conditions. Vacuum soldering and welding are treated with special reference to the merits of various fluxes. Methods of treating surfaces to reduce gas evolution are indicated. Vacuum seals and methods of testing hermetic properties are discussed. A V Balitskii, Book publd bja “Etler,vi_w”, Mo,sc,o,~-Lrtlitlrad, 1966. (in Russian). 20 546. Computer-designed vacuum vessels. (USA) Many chemical processes require vessels operating under partial vacuum; these can be designed using the American Society of Mechanical Engineers Code for Unfired Pressure Vessels, Section 8. Vacuum charts were used to obtain formulae capable of computer solution. A computer programme was derived to give optimum designs for different sets of conditions, resulting in savings in material and time. Some of the problems encountered in programming the charts and their solutions are discussed. C A Restivo, J Enp Ind, 88, 1966, 251-257. 20 147 547. Vacuum system of ion-microprobe mass spectrometer. (USA) A mass spectrometer in which atoms from a 0.1 mm’ surface of a target are sputtered and ionized under bombardment by a beam of inert-gas ions has been perfected. To exploit the capabilities of this analytical tool for the detection of trace elements in solids, a drastic reduction of the instrumental background had to be achieved. This was accomplished by using spectroscopically pure structural material in the ion source and by eliminating all sources of hydrocarbons. In particular, since the presence of pump-oil contamination on the surface under analysis was readily detectable, the resulting cracking pattern obscured a large portion of the atomic-mass scale. A combination of liquid-nitrogen-trapped mercury diffusion pumps, zeolite sorption pumps and sputter ion pumps has reduced the
Classlfled
abstracts
548-558
instrumental background sufficiently to facilitate the routine parts-perbillion trace analysis of the surface and of the bulk of conducting and nonconducting solids. (Authors) A E Barrington et al, J Vat Sci Technol, 3 (5). Se@--Uct 1966,239-251. 20 : 16 : 18 548. Electron projector for investigations of adsorption and electron emission of alkali earth thin fihn emitters. (USSR) A simple apparatus for investigations of adsorption and electron emission of Cs films on W in a sphere field-emission electron projector is described. This projector is pumped to 5 x lo+ torr by Ti getter and then to 5 x lo-‘@ torr by the pumping effect of the BayardAlpert gauge type IM-12. Projector walls are cooled by liquid nitrogen. (USSR) V I Makukha, Pribory Tekh Eksper, 11 (5), SepOct 1966, 196-197 (in Russian) . 20 549 Description and performance of a molecular beam chamber to be used for cryopumplng and adsorption pumping studies. (USA) An aerodynamic molecular beam chamber has been constructed and operated. Design criteria, performance data, detector requirements and space simulation applications are discussed, Cryopumping was utilized to provide the required pumping speed and to reduce the scattering of the beam by the background gas. R F Brown and H J Heald, Am Inst Aeronautics Astronautics J, 1966, 147-153. 20 550. High temperature neutron ditfraction furnace. (USA) An induction transformer furnace for a neutron diffractometer is described. The furnace has been used for the examination of refrac-. tory carbides by neutron diffraction at temperatures up to 2500°C. M G Bowman et al, Rev Sci Instrum, 37 (ll), 1966, 1543-1544. 20 : 37 551. Furnaces for vacuum heat treatment. (France) Applications discussed are vacuum annealing of refractory metals, copper and stainless steels, hardening of high speed steels and die steels, and vacuum brazing techniques. Techniques used for programming and controlling temperature and monitoring vacuum pressures are compared with those used for conventional air and controlled atmosphere furnaces. F J Be&et, Metallurgic, 5, 1966, 159-164 (in French). 20 552. An evaluation of a bake-out procedure for small glass ultrahigh vacuum systems. (USA) A bakeout procedure for small UHV systems is described which ensures pressure well below lo-” torr. An optically dense zeolite trap and a valve were placed between diffusion pump and system. F Stebuisser, Illinois University, Urbana, 1966, 17 pages. 20 553. Material transport in a vacuum diffusion oven. (Germany) A simple method is presented for determining the amount and pressure distribution of a material (eg antimony) flowing from source to target in a double-zoned vacuum furnace. Values obtained for an antimony source are identical to measured values. J Pfeifer, Vakuum-Technik, 15 (lo), Dee 1966, 249-253 (in German), 21. PUMPS AND PUMP FLUIDS Ion pumping with constant restoration abstract number 519.
21 :16 of the sorbent surface. See
21 : 16 Kbretics of N,, Ar and HI adsorption by granules of different adsorbents cooled to liquid nltrogea temperatare. See abstract number 520. 21 : 16 Adsorption of oil vapour on pare metallic surfaces. See abstract number 527. 21 122 554. Pressure measurement for determination of the speed of high vacnum pumps. (Great Britain) Theoretical considerations regarding pump speed measurement and the problems associated with their practical application are discussed. The results of a series of experiments are presented in which the effect of the position of the vacuum gauge inside the test dome on the value obtained for the intrinsic speed of the pump is investigated. These experiments were designed to evaluate the AVS test dome specifications with regard to some recent recommendations. R B&i, Vacuum, 16 (ll), Nov 1966, 585-589.
_.
Ll
555. Monte Carlo analysis of pumping speed test dome performance for several vaponr diffusion pump geometries. (Great Britain) The Monte Carlo technique of analysing free molecular gas flow has been used to study the performance of two designs of test dome in measuring the speed of several different designs of vapour diffusion pump. This study shows how the effective speed of each pump changes with the design of the test dome used, as a result of the change in the angular input distribution of gas molecules to the pump, and that the effective speed of the pump in the presence of the test dome may be as much as 25 per cent higher than the speed with a cosine input distribution to the pump mouth. The speed indicated by the gauge on the IS0 recommended test dome corresponds within statistical error limits to the effective speed of the pump mouth in the presence of the test dome. For those who are interested in designing vacuum system tubulation, vapour traps, and even diffusion pumps themselves, to take optimum advantage of the pumping effect of a vapour jet it would be more useful to characterise pump performance by the effective capture coeficient of the top jet vapour stream. rather than by a speed at the pump mouth. This capture coefficient could be calculated by Monte Carlo analysis from normal pumping speed test dome observations, and a knowledge of the internal geometry of the pump. (Author) J N Chubb, Vacuum, 16 (ll), Nov 1966, 591-596. 21 556. Effect on the measured pumping speed of a diffusion pump of the test head sire and the position of the pressure gauge and air inlet. (Great Britain) Experimental results of pump speed measurements with a number of test dome arrangements are reported for a 6-in diffusion pump. Both the test dome diameter and its effective length were varied while the pressure measuring position was moved along the length of the test dome. Two positions of the gas inlet tube were used and for one of these the effect of a gas diffusing baffle was investigated to improve the gas flow pattern at the top of the dome. From the results obtained with a test dome of the same internal diameter D as the mouth of the pump and effective length D, and with the gauge positioned at D/Z the measured speed was, within experimental error, equal to that measured with a 19-in. diameter vessel. On the other hand measurements with a gauge connected to the pump mouth would have given a “speed” figure of from 10-14 per cent higher. The influence of gas inlet imperfections, any disturbance to the gas flow and errors in the interpretation of pressure measurements from ionization gauge readings are discussed in the light of the experimental results obtained. B L Bateset al, Vacuum, 16 (11). Nov 1966, 597-600. 21 557. Evaluation of high vacuum pumps. (Great Britain) The speed of a pump depends not only upon the properties of the pump itself but generally also upon the velocity- and angle-distribution of the gas molecules entering the pump. For the exact definition of the speed therefore these influences besides other parameters, eg the nature of the gas, must be known. Consequently the effective speed, for instance, of the combination of a pump and a batBe or of a pump and a length of pipe can be calculated from the intrinsic speed S’ of the pump, if the value of S’ includes the angle distribution as produced by the baffle or pipe respectively. S’ generally is not identical with the intrinsic speed S that corresponds to the cosine-distribution of the incoming molecules. The backstreaming rate of pump fluid lies between zero and a maximum value of R-n depending on the state of the vacuum container. It is therefore suggested to specify R -being a characteristic quantity for the pump proper-instead of the actual backstreaming rate which may vary in each individual case. (Author) H G Noller, Vacuum, 16 (ll), Nov 1966, 613-618. 21 : 25 558. A method of measuring back migration of oil through a baffle. (Great Britain) A direct method is described for measuring the back migration rate of oil from a baffled diffusion pump using a liquid nitrogen cooled collector. Some experimental results are presented which show that migration rates equivalent to contaminant layer growths of a few Angstroms per hour can be measured. The advantages and limitations of the method are discussed. (Authors) R D Oswald and D J Crawiey, Vacuum, 16 (ll), Nov 1966, 623-624. 189
abstracts
537-547
the major reaction products observed. A comparison of experimental cross sections and corresponding rate constants for thermal-energy ions is made with theory. Measurements of the kinetic energy distributions of the ionic reaction products are also reported. T F Moran and L Friedman, J Chem Phys, 45 (IO), 15th Nov 1966, 3837-3845. 18 ~37 537. Electrical explosion of wires in air and in vacua. (USSR) Experiments on the explosion of copper wires by an electric current in air and in vacua are described. The current was obtained from a condenser battery yielding a 150 A discharge lasting for 40 ,ccsec. The copper sample, 85 mm long and 0.3 mm in diameter, was clamped in a stainless-steel cylinder provided with observation windows and evacuated to 2r 10-j torr. The nature of the explosion produced in the vacuum chamber was essentially different from explosions produced in air; evidence of this included spectroscopic records of the plasma associated with the explosions and the form of the respective volt/ampere characteristics. E K Chekalin and V S Shumanov, Book, “Research in Physical Gus Dynamics”, Moscow, 1966, 109, (in Russian). 18 538. The role of the material composing the central part of the cathode in a Penning-type discharge. (USSR) The role of the cathode material in determining the discharge current, over-all efficiency, and other parameters of Penning-type discharges is discussed. Since the state of the electrode surfaces changes rapidly in low-pressure discharges, particular attention must be paid to the reproducibility of the conditions when studying discharge parameters -failure to observe this has led to discrepancies in earlier-published data. New equipment ensuring reproducible conditions for Penningtype discharges at pressures of lo-” to lo-” torr is described. The material composing the central part of the cathode has a particularly severe effect on the discharge current when high-energy ions are passing along the axis. This effect increases as the work function of the cathode material falls. E M Reikhrudel’ et al, Radiotekh Elekfrotr, 11, ( I!) 1966, 2095-2098, (in Russian). 18 539. Instabilities in Penning discharges. (USA) Generation of electromagnetic energy in the microwave region in a cold-cathode Penning discharge at air pressures of 1 to 10 microns was studied using aluminium and graphite cathodes. B Agdur and U Ternstrom, Phys Rev Letters 13, 1965, 5-7. I8 540. First-order coupled wave equations for propagation in stratified compressible plasmas. (Australia) This paper deals with wave propagation in planar stratified, continuously varying, compressible, non-magnetized electron plasmas. The waves are coupled electromagnetic and electron acoustic waves, and are described by Maxwell’s equations coupled to the linearized single-fluid equations of hydrodynamics. Some first-order coupled wave equations are obtained and are transformed into convenient forms. Coupling, power flow, and approximate solutions are then discussed. (Authors). R Burman, Aus J Phys, 19, 1966, 747-757. 18 541. Non-equilibrium ionization growth in molecular hydrogen. (Australia) A thin-film cathode is used in an examination of the spatial growth of ionization in molecular hydrogen at high values of the parameter E/p (E is the electric field strength in V/cm, p is the gas pressure in torr at 0°C). Particular attention is given to the region of small gap separations d where non-equilibrium ionization growth occurs. The effect of non-uniformity of the electric field in this region due to anode perforations is demonstrated and the consequences of including ionization current measurements at small values of d in analyses of growth of current measurements are discussed. The variation of the “effective” Townsend coefficient a/p with E/p in uniform field conditions is obtained for values of E/p up to 1000 V crn~’ torr’. (Authors). S C Haydon and H M P Stock, Aus J Phys, 19, 1966, 795-803. I8 542. Electron drift and diffusion in deuterium at 293 K. (Australia) The drift velocity and the ratio of diffusion coefficient to mobility have been measured for electrons in deuterium at 293;K over the
188
ranges 0.006
respectively. (Authors).
The
18 543. Interaction of thermal electronics with polar molecules. (Austrdiia) Drift velocities of thermal electron swarms have been measured in pure ethylene gas and in mixtures of acetone, ethanolamine, ethylene diamine, ethanol, n-propanol, iso-propanol, chlorobenzene, dethyl ether, diethylamine, and propane with ethylene in a parallel plate ionization chamber evacuated by a 2 inch diameter silicone oil diffusion pump and rotary backing pumps to approximately IO-” torr. Cross sections for momentum transfer from electron to polar molecule deduced from these experiments and the literature arc compared with published “point dipole” theories. N Hamilton and J A D Stockdale, Arts J P/I_I,.s,19, 1966. 8 13-822. 18 544. Dependence of gas discharge maintaining voltage on the interelectrode distance. (USSR) Volt-centimeter characteristics of a gas discharge at ditrerent currents were investigated. The gas used was argon, and both electrodes were made from molybdenum. It is shown that for smaller currents the characteristics were displaced to the left side (to smaller critical distances). For interelectrode gaps larger than the critical distance, negative resistance with volt-ampere characteristics similar to those for subnormal glow discharge, but with far higher currents, may play a part. The possibility of the use of this negative resistance regime is briefly discussed and some recommendations to discharge tube designers are given. A E Ayzentson and N G Kashnikov, Zh Trkh Fiz. 36 ( I I), Nov 1966. 205 I -2055 (in Rnxsirrn).
II.
Vacuum
20. PUMPING
apparatus
and auxiliaries
SYSTEMS
20 : 34 Vacuum capabilities of the 150 cubic foot space facility at the Langley Research Centre. See abstract number 651. 20 545. Technology of vacuum equipment manufacture. (USSR) The conditions required for satisfactory operation of high-vacuum equipment are discussed and aspects of vacuum hygiene necessary for their fulfilment are considered. The types of materials best suited to vacuum work are discussed in relation to their gas-tightness and gas evolution under vacuum conditions. Vacuum soldering and welding are treated with special reference to the merits of various fluxes. Methods of treating surfaces to reduce gas evolution are indicated. Vacuum seals and methods of testing hermetic properties are discussed. A V Balitskii, Book publd bja “Etler,vi_w”, Mo,sc,o,~-Lrtlitlrad, 1966. (in Russian). 20 546. Computer-designed vacuum vessels. (USA) Many chemical processes require vessels operating under partial vacuum; these can be designed using the American Society of Mechanical Engineers Code for Unfired Pressure Vessels, Section 8. Vacuum charts were used to obtain formulae capable of computer solution. A computer programme was derived to give optimum designs for different sets of conditions, resulting in savings in material and time. Some of the problems encountered in programming the charts and their solutions are discussed. C A Restivo, J Enp Ind, 88, 1966, 251-257. 20 147 547. Vacuum system of ion-microprobe mass spectrometer. (USA) A mass spectrometer in which atoms from a 0.1 mm’ surface of a target are sputtered and ionized under bombardment by a beam of inert-gas ions has been perfected. To exploit the capabilities of this analytical tool for the detection of trace elements in solids, a drastic reduction of the instrumental background had to be achieved. This was accomplished by using spectroscopically pure structural material in the ion source and by eliminating all sources of hydrocarbons. In particular, since the presence of pump-oil contamination on the surface under analysis was readily detectable, the resulting cracking pattern obscured a large portion of the atomic-mass scale. A combination of liquid-nitrogen-trapped mercury diffusion pumps, zeolite sorption pumps and sputter ion pumps has reduced the
Classlfled
abstracts
548-558
instrumental background sufficiently to facilitate the routine parts-perbillion trace analysis of the surface and of the bulk of conducting and nonconducting solids. (Authors) A E Barrington et al, J Vat Sci Technol, 3 (5). Se@--Uct 1966,239-251. 20 : 16 : 18 548. Electron projector for investigations of adsorption and electron emission of alkali earth thin fihn emitters. (USSR) A simple apparatus for investigations of adsorption and electron emission of Cs films on W in a sphere field-emission electron projector is described. This projector is pumped to 5 x lo+ torr by Ti getter and then to 5 x lo-‘@ torr by the pumping effect of the BayardAlpert gauge type IM-12. Projector walls are cooled by liquid nitrogen. (USSR) V I Makukha, Pribory Tekh Eksper, 11 (5), SepOct 1966, 196-197 (in Russian) . 20 549 Description and performance of a molecular beam chamber to be used for cryopumplng and adsorption pumping studies. (USA) An aerodynamic molecular beam chamber has been constructed and operated. Design criteria, performance data, detector requirements and space simulation applications are discussed, Cryopumping was utilized to provide the required pumping speed and to reduce the scattering of the beam by the background gas. R F Brown and H J Heald, Am Inst Aeronautics Astronautics J, 1966, 147-153. 20 550. High temperature neutron ditfraction furnace. (USA) An induction transformer furnace for a neutron diffractometer is described. The furnace has been used for the examination of refrac-. tory carbides by neutron diffraction at temperatures up to 2500°C. M G Bowman et al, Rev Sci Instrum, 37 (ll), 1966, 1543-1544. 20 : 37 551. Furnaces for vacuum heat treatment. (France) Applications discussed are vacuum annealing of refractory metals, copper and stainless steels, hardening of high speed steels and die steels, and vacuum brazing techniques. Techniques used for programming and controlling temperature and monitoring vacuum pressures are compared with those used for conventional air and controlled atmosphere furnaces. F J Be&et, Metallurgic, 5, 1966, 159-164 (in French). 20 552. An evaluation of a bake-out procedure for small glass ultrahigh vacuum systems. (USA) A bakeout procedure for small UHV systems is described which ensures pressure well below lo-” torr. An optically dense zeolite trap and a valve were placed between diffusion pump and system. F Stebuisser, Illinois University, Urbana, 1966, 17 pages. 20 553. Material transport in a vacuum diffusion oven. (Germany) A simple method is presented for determining the amount and pressure distribution of a material (eg antimony) flowing from source to target in a double-zoned vacuum furnace. Values obtained for an antimony source are identical to measured values. J Pfeifer, Vakuum-Technik, 15 (lo), Dee 1966, 249-253 (in German), 21. PUMPS AND PUMP FLUIDS Ion pumping with constant restoration abstract number 519.
21 :16 of the sorbent surface. See
21 : 16 Kbretics of N,, Ar and HI adsorption by granules of different adsorbents cooled to liquid nltrogea temperatare. See abstract number 520. 21 : 16 Adsorption of oil vapour on pare metallic surfaces. See abstract number 527. 21 122 554. Pressure measurement for determination of the speed of high vacnum pumps. (Great Britain) Theoretical considerations regarding pump speed measurement and the problems associated with their practical application are discussed. The results of a series of experiments are presented in which the effect of the position of the vacuum gauge inside the test dome on the value obtained for the intrinsic speed of the pump is investigated. These experiments were designed to evaluate the AVS test dome specifications with regard to some recent recommendations. R B&i, Vacuum, 16 (ll), Nov 1966, 585-589.
_.
Ll
555. Monte Carlo analysis of pumping speed test dome performance for several vaponr diffusion pump geometries. (Great Britain) The Monte Carlo technique of analysing free molecular gas flow has been used to study the performance of two designs of test dome in measuring the speed of several different designs of vapour diffusion pump. This study shows how the effective speed of each pump changes with the design of the test dome used, as a result of the change in the angular input distribution of gas molecules to the pump, and that the effective speed of the pump in the presence of the test dome may be as much as 25 per cent higher than the speed with a cosine input distribution to the pump mouth. The speed indicated by the gauge on the IS0 recommended test dome corresponds within statistical error limits to the effective speed of the pump mouth in the presence of the test dome. For those who are interested in designing vacuum system tubulation, vapour traps, and even diffusion pumps themselves, to take optimum advantage of the pumping effect of a vapour jet it would be more useful to characterise pump performance by the effective capture coeficient of the top jet vapour stream. rather than by a speed at the pump mouth. This capture coefficient could be calculated by Monte Carlo analysis from normal pumping speed test dome observations, and a knowledge of the internal geometry of the pump. (Author) J N Chubb, Vacuum, 16 (ll), Nov 1966, 591-596. 21 556. Effect on the measured pumping speed of a diffusion pump of the test head sire and the position of the pressure gauge and air inlet. (Great Britain) Experimental results of pump speed measurements with a number of test dome arrangements are reported for a 6-in diffusion pump. Both the test dome diameter and its effective length were varied while the pressure measuring position was moved along the length of the test dome. Two positions of the gas inlet tube were used and for one of these the effect of a gas diffusing baffle was investigated to improve the gas flow pattern at the top of the dome. From the results obtained with a test dome of the same internal diameter D as the mouth of the pump and effective length D, and with the gauge positioned at D/Z the measured speed was, within experimental error, equal to that measured with a 19-in. diameter vessel. On the other hand measurements with a gauge connected to the pump mouth would have given a “speed” figure of from 10-14 per cent higher. The influence of gas inlet imperfections, any disturbance to the gas flow and errors in the interpretation of pressure measurements from ionization gauge readings are discussed in the light of the experimental results obtained. B L Bateset al, Vacuum, 16 (11). Nov 1966, 597-600. 21 557. Evaluation of high vacuum pumps. (Great Britain) The speed of a pump depends not only upon the properties of the pump itself but generally also upon the velocity- and angle-distribution of the gas molecules entering the pump. For the exact definition of the speed therefore these influences besides other parameters, eg the nature of the gas, must be known. Consequently the effective speed, for instance, of the combination of a pump and a batBe or of a pump and a length of pipe can be calculated from the intrinsic speed S’ of the pump, if the value of S’ includes the angle distribution as produced by the baffle or pipe respectively. S’ generally is not identical with the intrinsic speed S that corresponds to the cosine-distribution of the incoming molecules. The backstreaming rate of pump fluid lies between zero and a maximum value of R-n depending on the state of the vacuum container. It is therefore suggested to specify R -being a characteristic quantity for the pump proper-instead of the actual backstreaming rate which may vary in each individual case. (Author) H G Noller, Vacuum, 16 (ll), Nov 1966, 613-618. 21 : 25 558. A method of measuring back migration of oil through a baffle. (Great Britain) A direct method is described for measuring the back migration rate of oil from a baffled diffusion pump using a liquid nitrogen cooled collector. Some experimental results are presented which show that migration rates equivalent to contaminant layer growths of a few Angstroms per hour can be measured. The advantages and limitations of the method are discussed. (Authors) R D Oswald and D J Crawiey, Vacuum, 16 (ll), Nov 1966, 623-624. 189