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211. Density waves in low-pressure plasma columns
Classified abstracts 202--213 15. Fluid dynamics 15:22 202. A very highly sensitive micro-manometer. (Germany) A very sensitive micro-manometer has been developed for determining the pattern of flow rates m laminar flow of gases. K Elgeti and E R G Eckert, Chemie Ingenieur Techmk, 37 (11), Nov
1965, 1133-1136.
16. Gases and solids 16:47 203. Appfication of synthetic zeolites in the production of a clean vacuum. ( USSR) The adsorption capacities of A- and X-type zeohtes at low pressures and 77.5 °K were studied as functions of cation, complexing agent and conditions of preparation. Adsorption isotherms in the pressure range 1.333 × 10 -8 to 133.32 N / m 2, at liquid nitrogen temperature were determined by the volumetric method for adsorption of nitrogen, argon and hydrogen. Pressure measurement was by a combined system of mercury, thermocouple and lomzation gauges. Rates of adsorption of argon and nitrogen were comparatively similar, following the sequence: CaA > NaX > CaX > NaA. Hydrogen adsorption was in all cases very small amounting to about 5 × 10 -8 mg/Kg at 133.32 N / m s. The results show that the CaA zeohte is the most suitable for application to the production of low pressures or the cleaning of vacuum systems. The performance of the zeohtes, in adsorption of gases at low pressures, as superior to all other adsorbing media with the exception of carbon. Further research may well take the synthetic zeolite into first place. V M Lunev, Physics of plasma and problems of controlled thermo-
nuclear synthesis, 4, 1965, 488-494, (m Russian). 16 204. Sorption of gases on metal surfaces in ultra-high vacuum. (USA) B Berganov-Hansen et al, Stanford Research Institute, Califorma.
Quarterly Report No 8. 16 : 21 205. Adsorption properties of A-type zeolites at liquid nitrogen temperature. ( USSR) Samples of CaA, CaNaA and MgNaA were obtained from the sodium zeolite by a process of ion exchange. The rates of adsorption of nitrogen, argon and hydrogen on these materials at liquid nitrogen temperature, under vacuum, were determined. Adsorption lsothersm were measured by the volumetric method, using 10 g samples of zeolite of granule size 2 mm diameter and 3 to 15 mm long. Regeneration at 350-400°C, under vacuum, followed by cooling to hquid nitrogen temperature resulted m a pressure drop to 10-7 tort in two hours. The results indicate that internal diffusion in the zeolite layer is the rate-controlhng factor and that the adsorption process at low temperature and constant pressure is very slow. Under static conditions, pressures lower than 10 -7 torr may be achieved by these materials but their slow adsorption rates preclude their use in high speed pumping systems. It is suggested that since the rate of adsorption increases with increasing pressure, they may find application in sub-chambers of vacuum systems. It was found that the adsorption capacity varied widely with the cation form of the zeolite, over the pressure range 10-s to 100 torr. Zeohtes m which the degree of cation substitution is maximum are recommended for use m adsorption pumps. V M Lunev and A A Romanov, Zh Tekh Fiz, 35 (9), 1965, 1667, (in
Russian).
t7. T h e r m o d y n a m i c s 17
206. Experimental studies of hydrogen condensation on to liquid helium cooled surfaces. (Great Britain) Preliminary experimental studies of condensation pumping of hydrogen by liquid helium cooled surfaces were made using an unshielded 63 em z plane condensing surface. Values of sticking coefficients close to unity were obtained with no apparent dependence upon gas flow rate, in the range 1.5 x 10-3 to 17 × 10 -3 litre torr cm -3 see-x, upon the condensed gas load, up to 25 litre torr cm -3, or upon the surface temperature, in the range 3.6 to 3.9°K. Monte Carlo computer analysis of the gas flow was used to take account of pressure gradients developed in the test apparatus. The appearance of the layers of condensed hydrogen was sometimes clear and "ice"-like and sometimes white and "frost"-hke, even with apparently identical experimental con&tions. More accurate measure-
104
ments of sticking coefficients have been made by studying the reflection of hydrogen gas molecules from liquid helium cooled surfaces Monte Carlo analysis of probable molecular histories was used to interpret experimental measurements in terms of sticking coefficients Studies have been made which show that the sticking coefficient for hydrogen on surfaces at 3 5 or 3.7 °K varied from 0.98 to 0.99 for a gas temperature of 100°K, to 0.91 to 0.93 for a gas temperature of 300°K, and down to between 0.5 and 0.7 for a gas temperature of 700°K. Condensed hydrogen layers up to several milhmetres thick have recently been grown and are observed to be quite clear and transparent. Somewhat reduced sticking coefficients are observed as layers of these thicknesses are approached, and this reduction IS attributed to thermal conduction hmitat]ons in the condensedlayer. (GreatBrltam) (Authors) J N Chubb and I E Pollard, Vacuum, 15 (10), Oct 1965, 491-496
18. Gaseous electronics 18
208. Formation of plasmoids in pulsed plasma accelerators. (USSR) A pulsed discharge across the ends of a coaxial electrode in a vacuum (p <~10 -~ mmHg) is studied with the aim of elucidating the effects of electrode material and geometry. B A Osadin, Zh Tekh Flz, 35 (7), July 1965, 1327-1329. 18 209. The low afterglow emission as an indication of the state of electrode surfaces in vacuum breakdown tests. (USSR) P N Chistyakov and N V Tatarinova, Zh Tekh Fiz, 35 (7), July 1965,
1333-1335. lg 210. Breakdown mechanism of a discharge in crossed electric and magnetic fields in high vacuum. (USSR) The lmtlatlon of a discharge in a plane magnetron with a cold cathode in high vacuum ]s examined theoretically taking account o f collisions between electrons and gas atoms. E M Reikhrndel' and E P Sheritov, Zh Tekh Ftz, 35 (7), July 1965,
1255-1261 18 211. Density waves in low-pressure plasma columns. (Great Britain) Density waves in low-pressure arc discharges have been observed travelling towards the anode with speeds near (KT~/M)t. A disperslon relation for these waves is developed, taking into account the boundary effects, namely the continuous loss of ions to the contaming wails. L C Woods, JFluldMech, 23 (2), 1965, 315-323. 18 212. Ion trapping and gas release phenomena. (Great Britain) When energetic gas tons are injected into a sohd surface there is generally a high probability of their becoming trapped within the lattice and this process is of great technological importance in ion pumps and in physical applications where a gas discharge is in contact with a solid surface. In addition to the trapping process, there exist unfortunately, two mechanisms via which the trapped gas can re-evolve. The first is a purely thermally activated phenomenon which occurs without operation of further ion bombardment, whilst the second occurs during bombardment itself and is some form of sputtering phenomenon In this review the basic physical interactions involved in both the trapping and re-emission processes are examined, and the relevant literature which gives the magnitude of the effects, is surveyed. In particular is summarized the measured probability of trapping of inert gas ions at metal and insulator surfaces and how this is related to mteratomic forces is shown. The process responsible for thermal gas release is investigated, which Is ~hown to be diffusion controlled, and the available data correlated for bombardment induced gas release, for which the physical phenomenon is less definable Finally, the manner in which trapped atoms dissolve in the solid target is studied and it is shown how individual atoms can migrate and cluster to form bubbles Attention is directed wholly towards examination of inert gas lon-sol,d systems since chemical reactions can be discounted but It is suggested that the basic physclal interaction with more active gases is similar. (Great Britain) (Authors) W A Grant and G Carter, Vacuum, 15 (10), Oct 1965, 477-490. 18 : 33 213. On the low pressure mercury-vapour discharge mechanism and the origin of Langmuir's paradox. (Great Britain) Anon, Internat J Electronics, 18 (6), June 1965, 569-594.
1965, 1133-1136.
16. Gases and solids 16:47 203. Appfication of synthetic zeolites in the production of a clean vacuum. ( USSR) The adsorption capacities of A- and X-type zeohtes at low pressures and 77.5 °K were studied as functions of cation, complexing agent and conditions of preparation. Adsorption isotherms in the pressure range 1.333 × 10 -8 to 133.32 N / m 2, at liquid nitrogen temperature were determined by the volumetric method for adsorption of nitrogen, argon and hydrogen. Pressure measurement was by a combined system of mercury, thermocouple and lomzation gauges. Rates of adsorption of argon and nitrogen were comparatively similar, following the sequence: CaA > NaX > CaX > NaA. Hydrogen adsorption was in all cases very small amounting to about 5 × 10 -8 mg/Kg at 133.32 N / m s. The results show that the CaA zeohte is the most suitable for application to the production of low pressures or the cleaning of vacuum systems. The performance of the zeohtes, in adsorption of gases at low pressures, as superior to all other adsorbing media with the exception of carbon. Further research may well take the synthetic zeolite into first place. V M Lunev, Physics of plasma and problems of controlled thermo-
nuclear synthesis, 4, 1965, 488-494, (m Russian). 16 204. Sorption of gases on metal surfaces in ultra-high vacuum. (USA) B Berganov-Hansen et al, Stanford Research Institute, Califorma.
Quarterly Report No 8. 16 : 21 205. Adsorption properties of A-type zeolites at liquid nitrogen temperature. ( USSR) Samples of CaA, CaNaA and MgNaA were obtained from the sodium zeolite by a process of ion exchange. The rates of adsorption of nitrogen, argon and hydrogen on these materials at liquid nitrogen temperature, under vacuum, were determined. Adsorption lsothersm were measured by the volumetric method, using 10 g samples of zeolite of granule size 2 mm diameter and 3 to 15 mm long. Regeneration at 350-400°C, under vacuum, followed by cooling to hquid nitrogen temperature resulted m a pressure drop to 10-7 tort in two hours. The results indicate that internal diffusion in the zeolite layer is the rate-controlhng factor and that the adsorption process at low temperature and constant pressure is very slow. Under static conditions, pressures lower than 10 -7 torr may be achieved by these materials but their slow adsorption rates preclude their use in high speed pumping systems. It is suggested that since the rate of adsorption increases with increasing pressure, they may find application in sub-chambers of vacuum systems. It was found that the adsorption capacity varied widely with the cation form of the zeolite, over the pressure range 10-s to 100 torr. Zeohtes m which the degree of cation substitution is maximum are recommended for use m adsorption pumps. V M Lunev and A A Romanov, Zh Tekh Fiz, 35 (9), 1965, 1667, (in
Russian).
t7. T h e r m o d y n a m i c s 17
206. Experimental studies of hydrogen condensation on to liquid helium cooled surfaces. (Great Britain) Preliminary experimental studies of condensation pumping of hydrogen by liquid helium cooled surfaces were made using an unshielded 63 em z plane condensing surface. Values of sticking coefficients close to unity were obtained with no apparent dependence upon gas flow rate, in the range 1.5 x 10-3 to 17 × 10 -3 litre torr cm -3 see-x, upon the condensed gas load, up to 25 litre torr cm -3, or upon the surface temperature, in the range 3.6 to 3.9°K. Monte Carlo computer analysis of the gas flow was used to take account of pressure gradients developed in the test apparatus. The appearance of the layers of condensed hydrogen was sometimes clear and "ice"-like and sometimes white and "frost"-hke, even with apparently identical experimental con&tions. More accurate measure-
104
ments of sticking coefficients have been made by studying the reflection of hydrogen gas molecules from liquid helium cooled surfaces Monte Carlo analysis of probable molecular histories was used to interpret experimental measurements in terms of sticking coefficients Studies have been made which show that the sticking coefficient for hydrogen on surfaces at 3 5 or 3.7 °K varied from 0.98 to 0.99 for a gas temperature of 100°K, to 0.91 to 0.93 for a gas temperature of 300°K, and down to between 0.5 and 0.7 for a gas temperature of 700°K. Condensed hydrogen layers up to several milhmetres thick have recently been grown and are observed to be quite clear and transparent. Somewhat reduced sticking coefficients are observed as layers of these thicknesses are approached, and this reduction IS attributed to thermal conduction hmitat]ons in the condensedlayer. (GreatBrltam) (Authors) J N Chubb and I E Pollard, Vacuum, 15 (10), Oct 1965, 491-496
18. Gaseous electronics 18
208. Formation of plasmoids in pulsed plasma accelerators. (USSR) A pulsed discharge across the ends of a coaxial electrode in a vacuum (p <~10 -~ mmHg) is studied with the aim of elucidating the effects of electrode material and geometry. B A Osadin, Zh Tekh Flz, 35 (7), July 1965, 1327-1329. 18 209. The low afterglow emission as an indication of the state of electrode surfaces in vacuum breakdown tests. (USSR) P N Chistyakov and N V Tatarinova, Zh Tekh Fiz, 35 (7), July 1965,
1333-1335. lg 210. Breakdown mechanism of a discharge in crossed electric and magnetic fields in high vacuum. (USSR) The lmtlatlon of a discharge in a plane magnetron with a cold cathode in high vacuum ]s examined theoretically taking account o f collisions between electrons and gas atoms. E M Reikhrndel' and E P Sheritov, Zh Tekh Ftz, 35 (7), July 1965,
1255-1261 18 211. Density waves in low-pressure plasma columns. (Great Britain) Density waves in low-pressure arc discharges have been observed travelling towards the anode with speeds near (KT~/M)t. A disperslon relation for these waves is developed, taking into account the boundary effects, namely the continuous loss of ions to the contaming wails. L C Woods, JFluldMech, 23 (2), 1965, 315-323. 18 212. Ion trapping and gas release phenomena. (Great Britain) When energetic gas tons are injected into a sohd surface there is generally a high probability of their becoming trapped within the lattice and this process is of great technological importance in ion pumps and in physical applications where a gas discharge is in contact with a solid surface. In addition to the trapping process, there exist unfortunately, two mechanisms via which the trapped gas can re-evolve. The first is a purely thermally activated phenomenon which occurs without operation of further ion bombardment, whilst the second occurs during bombardment itself and is some form of sputtering phenomenon In this review the basic physical interactions involved in both the trapping and re-emission processes are examined, and the relevant literature which gives the magnitude of the effects, is surveyed. In particular is summarized the measured probability of trapping of inert gas ions at metal and insulator surfaces and how this is related to mteratomic forces is shown. The process responsible for thermal gas release is investigated, which Is ~hown to be diffusion controlled, and the available data correlated for bombardment induced gas release, for which the physical phenomenon is less definable Finally, the manner in which trapped atoms dissolve in the solid target is studied and it is shown how individual atoms can migrate and cluster to form bubbles Attention is directed wholly towards examination of inert gas lon-sol,d systems since chemical reactions can be discounted but It is suggested that the basic physclal interaction with more active gases is similar. (Great Britain) (Authors) W A Grant and G Carter, Vacuum, 15 (10), Oct 1965, 477-490. 18 : 33 213. On the low pressure mercury-vapour discharge mechanism and the origin of Langmuir's paradox. (Great Britain) Anon, Internat J Electronics, 18 (6), June 1965, 569-594.