- Email: [email protected]
1436. A plate-stator vacuum pump
Classified abstracts 1425-1436 for determination of the efficiency of inelastically reflected electrons in generation of slow secondary electrons. T L Matsekevich and A P Kazantsev, Izv A N S S S R Set Fiz, 37 (12), 1973, 2499-2501 (m Russian). 18 1425. Work function of elements in the model of ideal solid. (USSR) An approximation of strongly bound electrons is used for calculation of work function in vacuum of solid elements The results of calculations are compared with the experimental data. B P Nikonov, Izv A N S S S R Ser Fiz, 37 (12), 1973, 2502-2507 (in
Russian).
II. V a c u u m
a p p a r a t u s and auxiliaries
20. P U M P I N G SYSTEMS 20 1426. A cryopumping system for balloon-borne mass spectrometers. (USA) A change in geometry from that of the usual laboratory zeolite pump provided more efficient thermal insulation. Zeolite was packaged in a manner which gave a large surface-to-volume ratio and effective heat transfer during bakeout and cooling. R O Woods and T K Devlin, Rev Sct Instrum, 45 (1), 1974, 136-137. 2O 1427. Uniaxiai stress apparatus with analogue pressure readout. (USA) A unlaxlal stress apparatus with analogue pressure readout is described The apparatus allows measurements under vacuum and at low temperatures. (Germany) H Vogelmann and T A Fjeldly, Rev Sci Instrum, 45 (2), 1974, 309-310. 1428. An anaerobic stopped-flow spectrophotometer. (USA) 20 A reliable, all-glass, stopped-flow apparatus is described in which extremely air-sensitive reactions can be studied under anaerobic conditions; it is also suitable for studying reactions involving oxygen in solution. The equipment can be used over the temperature range --100 to +lO0°C. (UK) D Michael et al, Rev Sci lnstrum, 45 (2), 1974, 256-260. 20: 30 1429. A 'safe' high vacuum plant. (UK) When evaporating or sputtering poisonous substances and materials with high vapour pressures, the safety of the operator and the cleanliness of the vacuum plant are of major importance. An apparatus is described which improves the safety and cleanliness aspect of a vacuum plant. U Pick, JPhys E: Scient lnstrum, 7 (4), 1974, 249-250. 20 1430. Vacuum electric furnace for the heat treatment of parts. (USSR) This vacuum furnace differs from existing versions in that a preliminary heating chamber (also serving for the degassing of the samples) is placed over the main heating chamber, thus improving the quality of the heat treatment. The system contains a preliminary-evacuation unit with a raising and lowering device attached, the sample being firmly fixed in the latter. The heating chamber constituted a cylindrical shell with a cooling coil on the outside; inside it are the main heater and a thermal-insulation screens. A liquid trap is situated in the upper part of the heating chamber. Independent pumping systems are provided for the individual chambers. V I Grishin et al, Soviet Patent, class C 21 d, 9/00, No 230850, claimed 17/8/66, published 4/9/72 (in Russian).
permit a considerable increase in the number of revolutions and, in addition, are optically tight over the entire radius. In making high performance discs which are superior to existing discs the above assertions have been confirmed by experiment. Von W Becker and W Nesseldreher, Vakuum-Tech, 23 (1), 1974, 12-15 (in German). 21 1432. Evaluation of a liquid-helium cryopumping system operating with an electron beam gun. (USA) A recently developed 14-kW 240 ° electron beam gun was installed in an 18-in. glass belljar pumped by a liquid-helium cryopumping system made by Air Liqmde, a French supplier of cryogenic pumps, The cryogenic pump has a speed of 6000 liter/sec for air. Pumping of hydrogen and helium is accomplished by bleeding in a small amount of argon which freezes on the helium reservoir and has a gettering effect on these gases. Experiments were conducted to determine the operating characteristics of this type of system when evaporating various materials such as aluminium, copper, and tantalum. Data taken during the evaporation runs consisted of major gases evolved, time for belljar pressure to recover to 10-7 torr range, pressure during evaporation, effectiveness of argon sublimator in reducing pressure, and pumpdown curves. It was found that using a liquid-helium cryopumping system in conjunction with an electron beam gun gives exceptional results. It would be particularly advantageous in the fabrication of MOS devices where extreme cleanliness is required. G Mongodin et al, J Vac Sci Technol, 11 (l), 1974, 340-343. 21 1433. A comparison of pumping speed measurement methods. (USA) In order to reconcile differences in ion pump speeds reported by American and European users, a comparison of pumping speed measurements using the Fischer-Mommsen (E. Fischer and H. Mommsen, Vacuum 17, 309 (1967)) method and the 3-gauge conductance method [Apparatus of AVS tentative standard 4.1, Suppl. III (b)] was made using a pump with a speed of about 230 l/s The results were checked against a third technique--the measurement of time required to exhaust a pipette of known volume and known initial pressme with the pump chamber pressure held constant. The pipette method and the Fisher-Mommsen method agree and the 3-gauge method results in speeds about 8 % higher. Data are presented showing the advantages and disadvantages of measuring pumping speeds with pure gases and with gas mixtures such as air. D R Denison and E S MeKee, J Vac Sct Technol, 11 (1), 1974, 337-339. 21 1434. Measurements of adsorption isotherms and pumping speed of helium on molecular sieve in the 10-11-10 -7 turr range at 4.2 K. (USA) The experimental data on helium adsorption isotherms for molecular sieve have been extended from 10 -7 to 10-tt tort. A commercially available cryopump CVR 1008 made by Excalibur was used for this investigation. It was found that, in general, the experimental points fall on a curve predicted by the Dubinin and Radushkevich theory down to 1 × 10- lo torr. Below this pressure the slope gets steeper and possible causes for this behaviour are being studied. When compared with bare copper surfaces, a 1.8-mm-thick layer of bonded molecular sieve 5A absorbs almost l0 s times more helium per unit area. The pumping speed remains high for leaks Q < 1 × 10 -6 torr l/s with coverages of 10 cm a (STP)/cm 2 adsorbent. Cryosorption looks very attractive for pumping large amounts of helium at low pressures and is therefore suitable for superconducting storage rings where the pumps have to operate inside superconducting magnet Dewars. H J Halama and J R Aggus, J Vac Sci Technol, 11 (1), 1974, 333-336.
21. PUMPS AND P U M P FLUIDS 21 1431. New high performance discs for turbo-moleculur pumps. (Germany) New high performance discs for tubo-molecular pumps have been developed based on the following: (1) Tests have shown that the compression ratio and the pumping speed are best at optical tightness of the discs. (2) In order to obtain the maximum compression ratios and pumping speeds very high circumferential speeds are necessary. These, however, are limited by the material strength of the blades. Discs have been found which, due to a favourable blade shape,
21 1435. An automatic Toepler pump control. (USA) A highly reliable Toepler pump control which makes use of photoconductive cells as mercury level sensors is described. H E Moore and V H Frahm, Rev Sci lnstrum, 45 (2), 1974, 299. 21 1436. A plate-stator vacuum pump. (USSR) Conventional plate-stator vacuum pumps comprise a vessel with an eccentric rotor and a sprung plate designed to separate the forcing and suction regions. In the new version here presented, the plate is
415
Classified abstracts 1 4 3 7 - 1 4 4 5
hinge-supported, with one end in a groove m a c h m e d m the inner wall o f the vessel, a n d it h a s the shape o f a circular arc when viewed m cross section. T h e absence of friction f r o m the sides o f the plate a n d the reductnon in shp velocity a l o n g the rotor achieved in thns way furnishes the right condntions for creating a reliable od-free p u m p , hght a n d of small d i m e n s i o n s I G Khisameev et al, Soriet Patent, cla~s F 04, c 25/02, No 370,367, claimed 4/1/71, pubhshed 15/2/73 (m Russian). 21 1437. An ion-sorption pump of the orbitron type. (USSR) Existing lon-sorpUon p u m p s of the orbitron type used in the m a n u facture o f electrical v a c u u m a p p a r a t u s contain a complex series o f heaters a n d getter stores whnch have to be frequently replenished, so rendering the system as a whole inefficient. T h e anm o f the present invention is to increase the period o f service by m i n i m l z m g the n u m b e r of d m m a n t l m g operations for replacing parts This is achieved by providing a n a d d l h o n a l space m the p u m p , limited by a n end reflector, t h r o u g h the o p e n m g of which the a n o d e projects O n the a n o d e section lying within the addlUonal space is a series o f bushings m a d e of better materials a n d held m place by low-meltmgpoint solder. By supplying a low heating current the solder m a y be melted a n d the getter material b r o u g h t into play as a n d when required. V A Ushakov et al, Sol,let Patent, class F 04 b, 37/00 and H 01 j, 41/00, No 354175, claimed 26/6/70, pubhshed 23/11/72 (in Russian) 21 33 1438. Apparatus with a cryogenic pump for studying field-emission cathodes. (USSR) A n a p p a r a t u s with a s u p e r - h i g h - v a c u u m h e h u m p u m p intended for s t u d y m g the field-emission cathodes used in the holographic m e t h o d o f correcting spherical aberration in the electron microscope is described. P r e h m i n a r y evacuation o f the c r y o p u m p Is achneved by m e a n s o f conventional backing a n d od-dnffuslon p u m p s . After the c r y o p u m p h a s been started, the v o l u m e b e m g evacuated m a y be sealed off f r o m the other p u m p s by m e a n s of a specml valve system. T h e evacuating element o f the c r y o p u m p comprises a l i q u i d - h e h u m vessel s u r r o u n d e d by copper walls at h e h u m temperature a n d a h q u t d - m t r o g e n vessel with a thermal screen. T h e limiting v a c u u m is 10- ~o torr, which is achieved 3 h after the helium h a s been poured in. O n e filling lasts for 15 h operation P A Stoyanov et al, Scientific Councdon Electron Microscopy, Academy o f Sciences o f the USSR, M o w o w (m Russian). 22. G A U G E S 22 1439. Investigation of the sensitivity of ionization-type vacuum gauges. (USA) A q u a n t i t a t w e analysts o f a large a n d representauve sample o f available data h a s been m a d e to determine the best criteria for predicting the relative sensitivities o f ionization-type v a c u u m gauges to dafferent gases. T h e molecular property o f the gas that correlates best with relative sensitivity is the i o n i z a h o n cross section cr (eV). T h e best ~r value to choose according to gauge type is as follows: 1. F o r highpressure lomzation gauges, a t r evaluated at 2/3 o f the aecelelatmg p o t e n h a l o f the gauge is the best choice 2 F o r B a y a r d - A l p e r t a n d t r m d e gauges, a n y o f three choices are of a p p r o x i m a t e l y equal value These are 100 eV o values, m a x n m u m ~ value for each gas, a n d a ~r evaluated at 2/3 o f the accelerating potential for each gauge. 3. For the A l p h a t r o n gauge, ~r values in the range 5000-10,000 eV provnde the best correlation. 4. F o r cold c a t h o d e nonizatnon gauges, insufficient data were available to c o m e to a n y conclusions. R Holanda, J Vac Sct Technol, 10 (6), 1973, 1133 1139. 22 1440. The tungsten evaporotion limit of hot-cathode ionization gauges. (USA) C o m p a r a t i v e m e a s u r e m e n t s o f pressures in the low 10- J2-torr range with hot-filament total a n d partial pressure gauges have s h o w n discrepancies which can be partly explained by the influence o f t u n g s t e n v a p o u r from the hot filament on the total pressure gauge readings (tungsten evaporation limit). T h e m e t h o d proposed by Alpert a n d Burltz, with a slight modlficahon, was used for estimates o f the tungsten e v a p o r a t i o n limit; i e , a second filament served as an auxlltory source of evaporated tungsten a t o m s Three gauges were tested, o n e g a u g e with a buried collector a n d two m o d u l a t e d Bayard Alpert 416
gauges. T h e experiments showed that the tungsten evaporation h m l t s of all three gauges fell in the range (1-2) 10 ~2 torr (mtrogen e q m v a l e n t pressure) with an electron emission of 10 m A . Provided the variation o f the gauge sensltwlty with the emission ts known, it ns r e c o m m e n d e d to operate at reduced emission (e,g, 4 mA), at which level the t u n g s t e n limit is substantially lower Low-work-function emitters, as a m e a n s to o b t a m a low-temperature election source, were not covered by the present study, which a i m e d at determining s o m e p e r f o r m a n c e llmntattons at very low pressures o f a large n u m b e r o f existing gauges equipped with t u n g s t e n filaments (Switzerland) B Angerth and Z Hulek, J l/ac Sci Technol, 11 (1), 1974. 461-465 ,~r~
1441. A sensor based on silicon tensoresisturs for measurement of small pressure differences. (USSR) C o n s t r u c t i o n o f a silicon tensometric sensor for m e a s u r e m e n t o f small pressure differences m the range o f 0 to 80 m m H 2 0 is described. Utlhzatlon o f silicon tensoreslstors provides a high sensitivity o f 1 to 3 m V / m m H 2 0 . G R Grek et al, Prlb Tekh Eksper, No 4, 1973, 243-245 (m Russian) 22 1442. High-speed panoramatic radio-frequency mass spectrometer type R M S - 2 M . (USSR) T h e described high-frequency m a s s spectrometer of Bennet type with electron multiplier is intended for m o n i t o r i n g o f fast processes taking place in gas phase at thermal d e c o m p o s i t i o n a n d evaporation of materials In v a c u u m . T h e m a s s ranges are 2-12, 10-60 and 40200 a i n u at s c a n n i n g times o f 0 1 to 100 s T h e n o m i n a l resolutmn is 50 at 10% peak height. T h e sensitivity for a r g o n is 5 10 -9 torr at the scanning rate of 500 a m u / s T h e m a x i m u m working pressure is 5 10 ~ torr and the m i n i m u m detectable pressure 5 10 -t~ torz. V A Kaplin and E N Svobodin, PrttJ Te&h El~sper, No 4, 1973, 259
(tit Rtt~sslan). 23. P L U M B I N G 23 1443. A large, inexpensive, reliable rotary vacuum seal. (USA) A 57 cm n d rotating seal utilizing conventional ethylene propylene O - r m g s a n d rollers as a thrust bearing is described T h e seal is hand rotatable a n d s h o w s no pressure bursts at 3 10 7 torr R W Anderson, Rer S¢t In~trum, 45 (1), 1974, 122 23 1444. A cooled trap. (USSR) A n invention constituting an i m p r o v e m e n t to the conventional type o f cooled trap c o m p n s m g a simple vessel with a louvre system a n d a coolant reservoir furnished with a n anti-migration screen is descnbed. T h e a i m o f the m v e n h o n is to shorten the degassing period a n d reduce the consumptnon o f coolant To this end the screen ts m a d e in the form of a bellows set a r o u n d the perimeter of the inlet a n d connected to the louvre unit by m e a n s o f a ring placed in a socket in the wall o f the reservoir. V S Bongarev et ai, Sol'let Patent, clas~ F 04 f, 9/06, No 350,989, claimed 29/6/70, pubhshed 13/9/72 (m Russian). 24. VALVES 24 1445. A high vacuum valve with a programmed opening rate. ( U S A ) T h e basic m a s s flow c a p a c m e s of a d i f f u s i o n - p u m p - m e c h a n i c a l - p u m p c o m b i n a t i o n are reviewed. Overload condltnons for the diffusion p u m p are ndentlfied m the unstable region o f inlet pressures from 3 10 -~ to 3 l0 -3 torr depending on p u m p size Calculations s h o w that the high v a c u u m v a p o u r ,let ceases to function w h e n the ratio o f n u m b e r s o f p u m p e d gas molecules to motive fluid molecules exceeds 0 2 T o prevent the b r e a k d o w n of dnffuslon p u m p operation at high inlet pressures a special high v a c u u m valve Js proposed. T h e valve can be m a d e to a d m i t gas into the diffusion p u m p at a p r o g r a m m a b l e rate not exceeding the m a x n m u m t h r o u g h p u t of a given diffusion p u m p This is a c c o m p h s h e d by the use o f coupled p n e u m a t i c a n d h y d r a u h c actuators together with a c a m which controls a needle valve in the hydraulic circuit T h e flexlblhty of this a r r a n g e m e n t for a system operation is d e m o n s t r a t e d M H Hablanian and A A l,andfors, d Va~ Set Technol, II (I), 1974, 344
Russian).
II. V a c u u m
a p p a r a t u s and auxiliaries
20. P U M P I N G SYSTEMS 20 1426. A cryopumping system for balloon-borne mass spectrometers. (USA) A change in geometry from that of the usual laboratory zeolite pump provided more efficient thermal insulation. Zeolite was packaged in a manner which gave a large surface-to-volume ratio and effective heat transfer during bakeout and cooling. R O Woods and T K Devlin, Rev Sct Instrum, 45 (1), 1974, 136-137. 2O 1427. Uniaxiai stress apparatus with analogue pressure readout. (USA) A unlaxlal stress apparatus with analogue pressure readout is described The apparatus allows measurements under vacuum and at low temperatures. (Germany) H Vogelmann and T A Fjeldly, Rev Sci Instrum, 45 (2), 1974, 309-310. 1428. An anaerobic stopped-flow spectrophotometer. (USA) 20 A reliable, all-glass, stopped-flow apparatus is described in which extremely air-sensitive reactions can be studied under anaerobic conditions; it is also suitable for studying reactions involving oxygen in solution. The equipment can be used over the temperature range --100 to +lO0°C. (UK) D Michael et al, Rev Sci lnstrum, 45 (2), 1974, 256-260. 20: 30 1429. A 'safe' high vacuum plant. (UK) When evaporating or sputtering poisonous substances and materials with high vapour pressures, the safety of the operator and the cleanliness of the vacuum plant are of major importance. An apparatus is described which improves the safety and cleanliness aspect of a vacuum plant. U Pick, JPhys E: Scient lnstrum, 7 (4), 1974, 249-250. 20 1430. Vacuum electric furnace for the heat treatment of parts. (USSR) This vacuum furnace differs from existing versions in that a preliminary heating chamber (also serving for the degassing of the samples) is placed over the main heating chamber, thus improving the quality of the heat treatment. The system contains a preliminary-evacuation unit with a raising and lowering device attached, the sample being firmly fixed in the latter. The heating chamber constituted a cylindrical shell with a cooling coil on the outside; inside it are the main heater and a thermal-insulation screens. A liquid trap is situated in the upper part of the heating chamber. Independent pumping systems are provided for the individual chambers. V I Grishin et al, Soviet Patent, class C 21 d, 9/00, No 230850, claimed 17/8/66, published 4/9/72 (in Russian).
permit a considerable increase in the number of revolutions and, in addition, are optically tight over the entire radius. In making high performance discs which are superior to existing discs the above assertions have been confirmed by experiment. Von W Becker and W Nesseldreher, Vakuum-Tech, 23 (1), 1974, 12-15 (in German). 21 1432. Evaluation of a liquid-helium cryopumping system operating with an electron beam gun. (USA) A recently developed 14-kW 240 ° electron beam gun was installed in an 18-in. glass belljar pumped by a liquid-helium cryopumping system made by Air Liqmde, a French supplier of cryogenic pumps, The cryogenic pump has a speed of 6000 liter/sec for air. Pumping of hydrogen and helium is accomplished by bleeding in a small amount of argon which freezes on the helium reservoir and has a gettering effect on these gases. Experiments were conducted to determine the operating characteristics of this type of system when evaporating various materials such as aluminium, copper, and tantalum. Data taken during the evaporation runs consisted of major gases evolved, time for belljar pressure to recover to 10-7 torr range, pressure during evaporation, effectiveness of argon sublimator in reducing pressure, and pumpdown curves. It was found that using a liquid-helium cryopumping system in conjunction with an electron beam gun gives exceptional results. It would be particularly advantageous in the fabrication of MOS devices where extreme cleanliness is required. G Mongodin et al, J Vac Sci Technol, 11 (l), 1974, 340-343. 21 1433. A comparison of pumping speed measurement methods. (USA) In order to reconcile differences in ion pump speeds reported by American and European users, a comparison of pumping speed measurements using the Fischer-Mommsen (E. Fischer and H. Mommsen, Vacuum 17, 309 (1967)) method and the 3-gauge conductance method [Apparatus of AVS tentative standard 4.1, Suppl. III (b)] was made using a pump with a speed of about 230 l/s The results were checked against a third technique--the measurement of time required to exhaust a pipette of known volume and known initial pressme with the pump chamber pressure held constant. The pipette method and the Fisher-Mommsen method agree and the 3-gauge method results in speeds about 8 % higher. Data are presented showing the advantages and disadvantages of measuring pumping speeds with pure gases and with gas mixtures such as air. D R Denison and E S MeKee, J Vac Sct Technol, 11 (1), 1974, 337-339. 21 1434. Measurements of adsorption isotherms and pumping speed of helium on molecular sieve in the 10-11-10 -7 turr range at 4.2 K. (USA) The experimental data on helium adsorption isotherms for molecular sieve have been extended from 10 -7 to 10-tt tort. A commercially available cryopump CVR 1008 made by Excalibur was used for this investigation. It was found that, in general, the experimental points fall on a curve predicted by the Dubinin and Radushkevich theory down to 1 × 10- lo torr. Below this pressure the slope gets steeper and possible causes for this behaviour are being studied. When compared with bare copper surfaces, a 1.8-mm-thick layer of bonded molecular sieve 5A absorbs almost l0 s times more helium per unit area. The pumping speed remains high for leaks Q < 1 × 10 -6 torr l/s with coverages of 10 cm a (STP)/cm 2 adsorbent. Cryosorption looks very attractive for pumping large amounts of helium at low pressures and is therefore suitable for superconducting storage rings where the pumps have to operate inside superconducting magnet Dewars. H J Halama and J R Aggus, J Vac Sci Technol, 11 (1), 1974, 333-336.
21. PUMPS AND P U M P FLUIDS 21 1431. New high performance discs for turbo-moleculur pumps. (Germany) New high performance discs for tubo-molecular pumps have been developed based on the following: (1) Tests have shown that the compression ratio and the pumping speed are best at optical tightness of the discs. (2) In order to obtain the maximum compression ratios and pumping speeds very high circumferential speeds are necessary. These, however, are limited by the material strength of the blades. Discs have been found which, due to a favourable blade shape,
21 1435. An automatic Toepler pump control. (USA) A highly reliable Toepler pump control which makes use of photoconductive cells as mercury level sensors is described. H E Moore and V H Frahm, Rev Sci lnstrum, 45 (2), 1974, 299. 21 1436. A plate-stator vacuum pump. (USSR) Conventional plate-stator vacuum pumps comprise a vessel with an eccentric rotor and a sprung plate designed to separate the forcing and suction regions. In the new version here presented, the plate is
415
Classified abstracts 1 4 3 7 - 1 4 4 5
hinge-supported, with one end in a groove m a c h m e d m the inner wall o f the vessel, a n d it h a s the shape o f a circular arc when viewed m cross section. T h e absence of friction f r o m the sides o f the plate a n d the reductnon in shp velocity a l o n g the rotor achieved in thns way furnishes the right condntions for creating a reliable od-free p u m p , hght a n d of small d i m e n s i o n s I G Khisameev et al, Soriet Patent, cla~s F 04, c 25/02, No 370,367, claimed 4/1/71, pubhshed 15/2/73 (m Russian). 21 1437. An ion-sorption pump of the orbitron type. (USSR) Existing lon-sorpUon p u m p s of the orbitron type used in the m a n u facture o f electrical v a c u u m a p p a r a t u s contain a complex series o f heaters a n d getter stores whnch have to be frequently replenished, so rendering the system as a whole inefficient. T h e anm o f the present invention is to increase the period o f service by m i n i m l z m g the n u m b e r of d m m a n t l m g operations for replacing parts This is achieved by providing a n a d d l h o n a l space m the p u m p , limited by a n end reflector, t h r o u g h the o p e n m g of which the a n o d e projects O n the a n o d e section lying within the addlUonal space is a series o f bushings m a d e of better materials a n d held m place by low-meltmgpoint solder. By supplying a low heating current the solder m a y be melted a n d the getter material b r o u g h t into play as a n d when required. V A Ushakov et al, Sol,let Patent, class F 04 b, 37/00 and H 01 j, 41/00, No 354175, claimed 26/6/70, pubhshed 23/11/72 (in Russian) 21 33 1438. Apparatus with a cryogenic pump for studying field-emission cathodes. (USSR) A n a p p a r a t u s with a s u p e r - h i g h - v a c u u m h e h u m p u m p intended for s t u d y m g the field-emission cathodes used in the holographic m e t h o d o f correcting spherical aberration in the electron microscope is described. P r e h m i n a r y evacuation o f the c r y o p u m p Is achneved by m e a n s o f conventional backing a n d od-dnffuslon p u m p s . After the c r y o p u m p h a s been started, the v o l u m e b e m g evacuated m a y be sealed off f r o m the other p u m p s by m e a n s of a specml valve system. T h e evacuating element o f the c r y o p u m p comprises a l i q u i d - h e h u m vessel s u r r o u n d e d by copper walls at h e h u m temperature a n d a h q u t d - m t r o g e n vessel with a thermal screen. T h e limiting v a c u u m is 10- ~o torr, which is achieved 3 h after the helium h a s been poured in. O n e filling lasts for 15 h operation P A Stoyanov et al, Scientific Councdon Electron Microscopy, Academy o f Sciences o f the USSR, M o w o w (m Russian). 22. G A U G E S 22 1439. Investigation of the sensitivity of ionization-type vacuum gauges. (USA) A q u a n t i t a t w e analysts o f a large a n d representauve sample o f available data h a s been m a d e to determine the best criteria for predicting the relative sensitivities o f ionization-type v a c u u m gauges to dafferent gases. T h e molecular property o f the gas that correlates best with relative sensitivity is the i o n i z a h o n cross section cr (eV). T h e best ~r value to choose according to gauge type is as follows: 1. F o r highpressure lomzation gauges, a t r evaluated at 2/3 o f the aecelelatmg p o t e n h a l o f the gauge is the best choice 2 F o r B a y a r d - A l p e r t a n d t r m d e gauges, a n y o f three choices are of a p p r o x i m a t e l y equal value These are 100 eV o values, m a x n m u m ~ value for each gas, a n d a ~r evaluated at 2/3 o f the accelerating potential for each gauge. 3. For the A l p h a t r o n gauge, ~r values in the range 5000-10,000 eV provnde the best correlation. 4. F o r cold c a t h o d e nonizatnon gauges, insufficient data were available to c o m e to a n y conclusions. R Holanda, J Vac Sct Technol, 10 (6), 1973, 1133 1139. 22 1440. The tungsten evaporotion limit of hot-cathode ionization gauges. (USA) C o m p a r a t i v e m e a s u r e m e n t s o f pressures in the low 10- J2-torr range with hot-filament total a n d partial pressure gauges have s h o w n discrepancies which can be partly explained by the influence o f t u n g s t e n v a p o u r from the hot filament on the total pressure gauge readings (tungsten evaporation limit). T h e m e t h o d proposed by Alpert a n d Burltz, with a slight modlficahon, was used for estimates o f the tungsten e v a p o r a t i o n limit; i e , a second filament served as an auxlltory source of evaporated tungsten a t o m s Three gauges were tested, o n e g a u g e with a buried collector a n d two m o d u l a t e d Bayard Alpert 416
gauges. T h e experiments showed that the tungsten evaporation h m l t s of all three gauges fell in the range (1-2) 10 ~2 torr (mtrogen e q m v a l e n t pressure) with an electron emission of 10 m A . Provided the variation o f the gauge sensltwlty with the emission ts known, it ns r e c o m m e n d e d to operate at reduced emission (e,g, 4 mA), at which level the t u n g s t e n limit is substantially lower Low-work-function emitters, as a m e a n s to o b t a m a low-temperature election source, were not covered by the present study, which a i m e d at determining s o m e p e r f o r m a n c e llmntattons at very low pressures o f a large n u m b e r o f existing gauges equipped with t u n g s t e n filaments (Switzerland) B Angerth and Z Hulek, J l/ac Sci Technol, 11 (1), 1974. 461-465 ,~r~
1441. A sensor based on silicon tensoresisturs for measurement of small pressure differences. (USSR) C o n s t r u c t i o n o f a silicon tensometric sensor for m e a s u r e m e n t o f small pressure differences m the range o f 0 to 80 m m H 2 0 is described. Utlhzatlon o f silicon tensoreslstors provides a high sensitivity o f 1 to 3 m V / m m H 2 0 . G R Grek et al, Prlb Tekh Eksper, No 4, 1973, 243-245 (m Russian) 22 1442. High-speed panoramatic radio-frequency mass spectrometer type R M S - 2 M . (USSR) T h e described high-frequency m a s s spectrometer of Bennet type with electron multiplier is intended for m o n i t o r i n g o f fast processes taking place in gas phase at thermal d e c o m p o s i t i o n a n d evaporation of materials In v a c u u m . T h e m a s s ranges are 2-12, 10-60 and 40200 a i n u at s c a n n i n g times o f 0 1 to 100 s T h e n o m i n a l resolutmn is 50 at 10% peak height. T h e sensitivity for a r g o n is 5 10 -9 torr at the scanning rate of 500 a m u / s T h e m a x i m u m working pressure is 5 10 ~ torr and the m i n i m u m detectable pressure 5 10 -t~ torz. V A Kaplin and E N Svobodin, PrttJ Te&h El~sper, No 4, 1973, 259
(tit Rtt~sslan). 23. P L U M B I N G 23 1443. A large, inexpensive, reliable rotary vacuum seal. (USA) A 57 cm n d rotating seal utilizing conventional ethylene propylene O - r m g s a n d rollers as a thrust bearing is described T h e seal is hand rotatable a n d s h o w s no pressure bursts at 3 10 7 torr R W Anderson, Rer S¢t In~trum, 45 (1), 1974, 122 23 1444. A cooled trap. (USSR) A n invention constituting an i m p r o v e m e n t to the conventional type o f cooled trap c o m p n s m g a simple vessel with a louvre system a n d a coolant reservoir furnished with a n anti-migration screen is descnbed. T h e a i m o f the m v e n h o n is to shorten the degassing period a n d reduce the consumptnon o f coolant To this end the screen ts m a d e in the form of a bellows set a r o u n d the perimeter of the inlet a n d connected to the louvre unit by m e a n s o f a ring placed in a socket in the wall o f the reservoir. V S Bongarev et ai, Sol'let Patent, clas~ F 04 f, 9/06, No 350,989, claimed 29/6/70, pubhshed 13/9/72 (m Russian). 24. VALVES 24 1445. A high vacuum valve with a programmed opening rate. ( U S A ) T h e basic m a s s flow c a p a c m e s of a d i f f u s i o n - p u m p - m e c h a n i c a l - p u m p c o m b i n a t i o n are reviewed. Overload condltnons for the diffusion p u m p are ndentlfied m the unstable region o f inlet pressures from 3 10 -~ to 3 l0 -3 torr depending on p u m p size Calculations s h o w that the high v a c u u m v a p o u r ,let ceases to function w h e n the ratio o f n u m b e r s o f p u m p e d gas molecules to motive fluid molecules exceeds 0 2 T o prevent the b r e a k d o w n of dnffuslon p u m p operation at high inlet pressures a special high v a c u u m valve Js proposed. T h e valve can be m a d e to a d m i t gas into the diffusion p u m p at a p r o g r a m m a b l e rate not exceeding the m a x n m u m t h r o u g h p u t of a given diffusion p u m p This is a c c o m p h s h e d by the use o f coupled p n e u m a t i c a n d h y d r a u h c actuators together with a c a m which controls a needle valve in the hydraulic circuit T h e flexlblhty of this a r r a n g e m e n t for a system operation is d e m o n s t r a t e d M H Hablanian and A A l,andfors, d Va~ Set Technol, II (I), 1974, 344