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On estimate of the time lag of breakdown of vacuum gaps
Classified abstracts 3468-3478 emissive and thermionic properties photocathode. The material may be converters and for the formation cathodes. T R Briere and A H Sommer, J Appl
of a silver-oxygen-cesium (S-l) of interest for thermionic energy of silver-oxygen-cesium photoPhys, 48 (8),
1977, 3547-3550.
3468. Kinetic temperature measurement of the front surface of a tar,hf exposed to an intense pulsed electron beam. (USA) A measurement of surface temperature has been developed for pulsed radiation dose levels such that vaporization of the material under investigation is obtained. This method, which has been successfully used, is based on the kinetic definition of temperature and can be used for temperatures above the vaporization threshold and beyond without changing the physical phenomena. A detector located at a distance I from the target establishes the speed distribution of atoms ejected, from which we deduce the temperature. The rise time of the leading portion of the signal obtained depends on the temperature. Compared to optical methods, this method has the advantage of being unaffected by the electromagnetic and bremsstrahlung noises inherent to electron generators. Moreover, the hydrodynamic expansion velocity can be calculated and the blowoff density estimated. This method can also be used in the case of other pulsed energy sources such as photons or ions. (France) C Peugnet,J Appl Phys, 48 (8). 1977,3206-3210. 12 3469. Enhancement of the rate of charge-exchange collisions in a He-Cd discharge. (USA) Spontaneous emission from the 5337 A and 5378 A transitions in Cd(H) was studied in a dc discharge whose positive column was exposed to microwave power. The intensities obtained were at least one and one-half times higher than those expected from input increasing with microwave power superposed. This enhancement is explained on the assumption that the electron temperature also increases with the microwave power. (Japan) S Chinen and S Hattori, J Appl Phys, 48 (8), 1977,3603-3604. 12 3470. Discharge studies of the N*Cu laser. (USA) Spontaneous emission and absorption studies of the Ne-Cu hollowcathode laser are summarized. The major discharge processes operative in the Ne-Cu laser are outlined and the qualitative aspects of a proposed model of the Ne-Cu laser are discussed. Emphasis is placed on cathode sputtering as a source of copper atoms and we demonstrate that copper densities of 1OL4 atoms/cm3 are createdvia discharge sputtering. F J de Hoog et al, J Appl Phys, 48 (9), 1977,3701-3704. 12 3471. Thermionic work function of LaB6 single crystals and their surfaces. (USA) The thermionic work functions and the Richardson constants for LaB6 single crystals have been measured using a diode system with a guard ring under stable thermionic conditions. They are2.86 f 0.03 eV, 82 AIcmZK2 for the (1001 olane. 2.68 + 0.03 eV. 57 Alcml K2 for the (i 10) plane and j.4 go.2 dV, 71 A/cm2 Ki for ihe (111) plane. The (111) faceting on the (110) plane has an important effect on the reduction of the thermionic current from the (110) plane at 5 x 10m6 torr. (Japan), C Oshima et al, J Appl Phys, 48 (9), 1977,3925-3927. 12 3472. Electron energy distributions from GaP with negative electron affinity. II. Near-uv photoemission and secondary emission. (USA) Near-uv photoelectron energy distributions and spectral quantum yields are measured on high-efficiency carbon-free (100) GaP epitaxial layers activated to negative electron affinity (NEA) with Cs or Cs and Oz. Energy distributions show that near-uv photoelectrons thermalire at both X and L conduction-band minima even for electronsexcited bydirect Fls” + Frc transitions. A two-valley diffusion model gives an accurate quantitative description of the quantum yields and is consistent with the observed energy distribution curves. Secondary-electron energy distributions are given. Thermalization effects at X and L conduction-band minima are also obvious here, but the proportion of hot electrons is higher than has generally been suspected up to now. The hot electron distributions show structure which corresponds to maxima and minima of the density of states in the conduction band at the surface. This can be used in a simple experiment to measure the amount of band bending at the surface. 154
1.65 and 1.4 eV are obtained for Cs and Cs-0 activated surfaces, respectively. (France) C Piaget and P Sage& J Appl Phys, 48 (9), 1977,3907-39 13. I2 3473. On estimate of the time lae of breakdown of vacuum gaps. (USSR) The dependence of the time lag of vacuum breakdown on the amplitude of pulse voltage is calculated for various cathode materials on the basis of calculation of temperature distribution in cathode microprojections at heating by thkrmal-field electron emission current. The calculated results agree well with the experimental data what indicates the validity of cathode initiating of pulse vacuum breakdown by Joule heating of emitter by thermal-field emission current. A A Emelyanov et al, Izv VUZ Fiz, No 4, 1976, 142-145 (in Russian). 12 3474. The influence of ion bombardment on electro-reflection and photoluminescence spectra of n-Al,Ga, -,As solid solutions. (USSR) The influence of 1 keV argon ion bombardment at a dose lOI ion/cm’ on electro-reflect& and photoluminescence spectra of epitaxial films of n-Al,Ga,-,As solid solutions is investigated. Experimental results are discussed. V I Gavrilenko et al, Fiz Tekh Polyp, 10 (2), 1976,3 1O-31 5 (in Russiun).
II.
Vacuum
21. PUMP
apparatus
AND
PUMP
and
auxiliaries
FLUIDS
21 3475. New turbomolecular pumps and their application in physics. (Germany) After a short explanation of the principle of turbo molecular pumps the characteristic data: compression, volume flow rate and the residual gas composition as well as the relations between these parameters are described. The influence of the structure of the blades on the performance of a pump is shortly discussed. Finally the most important applications in physics are shown. Von J Henning, Vukuum-Tech, 26 (61, 1977, 177-181 (in Germun). 21 3476. Pumping speed of a high vacuum sorption pump: determination of condens&on coefficients. (GB) A high vacuum sorotion oumo with a soeed of 14 I/s for air has been-developed and its &io;s characteristics are given. A final pressure of 2 x lo-’ torr was achieved by this pump in a two-stage pumping of air from 760 torr. The pumping speeds for various gases were investigated in the pressure range from 10m6 to lOwa torr. The condensation coefficients for these gases were evaluated from the respective pumping speeds and found to be 3.5 x 10e3, 3.9 x IO-“, 4.8 x lo-“, 2.1 x 10e3 and 0.4 for air, N1, Oz. Ar and C02, respectively. These results have been compared with the existing data. A dependence of the condensation coefficient on the gas pressure as well as on the quantity of the pumped gas was observed. The ultimate pressure attained significantly depended on the quantity of the preadsorbed gas. (India) C V G Nair and P Vijendran, Vacuum, 27 (9), 1977,549-553. 21 3477. Diffusion pump back-streaming. (GB) The development of the diffusion pump to attain ultra high vacua came about by concentrating on the elimination of contamination entering the vacuum system from the pump itself. This review deals exclusively with contamination which can be attributed to backstreaming of diffusion pump working fluid. It discusses the origins of this type of contamination, survey methods used to prevent and control it and shows that it is possible to produce a clean vacuum using such pumps. N S Harris, Vacuum, 27 (9), 1977,519-530. 22. GAUGES
AND
MEASUREMENT
OF LOW PRESSURES
22 3478. The design and study of a compact bakeable ultra-high vacuum system for calibrating absolutely low pressure gauges. (GB) .& compact stainless-steel &a-high vacuum system is designed, constructed and tested which enables anv vacuum gauge to be calibrated absolutely, quickly and reliably o;er the pressure range 10
of a silver-oxygen-cesium (S-l) of interest for thermionic energy of silver-oxygen-cesium photoPhys, 48 (8),
1977, 3547-3550.
3468. Kinetic temperature measurement of the front surface of a tar,hf exposed to an intense pulsed electron beam. (USA) A measurement of surface temperature has been developed for pulsed radiation dose levels such that vaporization of the material under investigation is obtained. This method, which has been successfully used, is based on the kinetic definition of temperature and can be used for temperatures above the vaporization threshold and beyond without changing the physical phenomena. A detector located at a distance I from the target establishes the speed distribution of atoms ejected, from which we deduce the temperature. The rise time of the leading portion of the signal obtained depends on the temperature. Compared to optical methods, this method has the advantage of being unaffected by the electromagnetic and bremsstrahlung noises inherent to electron generators. Moreover, the hydrodynamic expansion velocity can be calculated and the blowoff density estimated. This method can also be used in the case of other pulsed energy sources such as photons or ions. (France) C Peugnet,J Appl Phys, 48 (8). 1977,3206-3210. 12 3469. Enhancement of the rate of charge-exchange collisions in a He-Cd discharge. (USA) Spontaneous emission from the 5337 A and 5378 A transitions in Cd(H) was studied in a dc discharge whose positive column was exposed to microwave power. The intensities obtained were at least one and one-half times higher than those expected from input increasing with microwave power superposed. This enhancement is explained on the assumption that the electron temperature also increases with the microwave power. (Japan) S Chinen and S Hattori, J Appl Phys, 48 (8), 1977,3603-3604. 12 3470. Discharge studies of the N*Cu laser. (USA) Spontaneous emission and absorption studies of the Ne-Cu hollowcathode laser are summarized. The major discharge processes operative in the Ne-Cu laser are outlined and the qualitative aspects of a proposed model of the Ne-Cu laser are discussed. Emphasis is placed on cathode sputtering as a source of copper atoms and we demonstrate that copper densities of 1OL4 atoms/cm3 are createdvia discharge sputtering. F J de Hoog et al, J Appl Phys, 48 (9), 1977,3701-3704. 12 3471. Thermionic work function of LaB6 single crystals and their surfaces. (USA) The thermionic work functions and the Richardson constants for LaB6 single crystals have been measured using a diode system with a guard ring under stable thermionic conditions. They are2.86 f 0.03 eV, 82 AIcmZK2 for the (1001 olane. 2.68 + 0.03 eV. 57 Alcml K2 for the (i 10) plane and j.4 go.2 dV, 71 A/cm2 Ki for ihe (111) plane. The (111) faceting on the (110) plane has an important effect on the reduction of the thermionic current from the (110) plane at 5 x 10m6 torr. (Japan), C Oshima et al, J Appl Phys, 48 (9), 1977,3925-3927. 12 3472. Electron energy distributions from GaP with negative electron affinity. II. Near-uv photoemission and secondary emission. (USA) Near-uv photoelectron energy distributions and spectral quantum yields are measured on high-efficiency carbon-free (100) GaP epitaxial layers activated to negative electron affinity (NEA) with Cs or Cs and Oz. Energy distributions show that near-uv photoelectrons thermalire at both X and L conduction-band minima even for electronsexcited bydirect Fls” + Frc transitions. A two-valley diffusion model gives an accurate quantitative description of the quantum yields and is consistent with the observed energy distribution curves. Secondary-electron energy distributions are given. Thermalization effects at X and L conduction-band minima are also obvious here, but the proportion of hot electrons is higher than has generally been suspected up to now. The hot electron distributions show structure which corresponds to maxima and minima of the density of states in the conduction band at the surface. This can be used in a simple experiment to measure the amount of band bending at the surface. 154
1.65 and 1.4 eV are obtained for Cs and Cs-0 activated surfaces, respectively. (France) C Piaget and P Sage& J Appl Phys, 48 (9), 1977,3907-39 13. I2 3473. On estimate of the time lae of breakdown of vacuum gaps. (USSR) The dependence of the time lag of vacuum breakdown on the amplitude of pulse voltage is calculated for various cathode materials on the basis of calculation of temperature distribution in cathode microprojections at heating by thkrmal-field electron emission current. The calculated results agree well with the experimental data what indicates the validity of cathode initiating of pulse vacuum breakdown by Joule heating of emitter by thermal-field emission current. A A Emelyanov et al, Izv VUZ Fiz, No 4, 1976, 142-145 (in Russian). 12 3474. The influence of ion bombardment on electro-reflection and photoluminescence spectra of n-Al,Ga, -,As solid solutions. (USSR) The influence of 1 keV argon ion bombardment at a dose lOI ion/cm’ on electro-reflect& and photoluminescence spectra of epitaxial films of n-Al,Ga,-,As solid solutions is investigated. Experimental results are discussed. V I Gavrilenko et al, Fiz Tekh Polyp, 10 (2), 1976,3 1O-31 5 (in Russiun).
II.
Vacuum
21. PUMP
apparatus
AND
PUMP
and
auxiliaries
FLUIDS
21 3475. New turbomolecular pumps and their application in physics. (Germany) After a short explanation of the principle of turbo molecular pumps the characteristic data: compression, volume flow rate and the residual gas composition as well as the relations between these parameters are described. The influence of the structure of the blades on the performance of a pump is shortly discussed. Finally the most important applications in physics are shown. Von J Henning, Vukuum-Tech, 26 (61, 1977, 177-181 (in Germun). 21 3476. Pumping speed of a high vacuum sorption pump: determination of condens&on coefficients. (GB) A high vacuum sorotion oumo with a soeed of 14 I/s for air has been-developed and its &io;s characteristics are given. A final pressure of 2 x lo-’ torr was achieved by this pump in a two-stage pumping of air from 760 torr. The pumping speeds for various gases were investigated in the pressure range from 10m6 to lOwa torr. The condensation coefficients for these gases were evaluated from the respective pumping speeds and found to be 3.5 x 10e3, 3.9 x IO-“, 4.8 x lo-“, 2.1 x 10e3 and 0.4 for air, N1, Oz. Ar and C02, respectively. These results have been compared with the existing data. A dependence of the condensation coefficient on the gas pressure as well as on the quantity of the pumped gas was observed. The ultimate pressure attained significantly depended on the quantity of the preadsorbed gas. (India) C V G Nair and P Vijendran, Vacuum, 27 (9), 1977,549-553. 21 3477. Diffusion pump back-streaming. (GB) The development of the diffusion pump to attain ultra high vacua came about by concentrating on the elimination of contamination entering the vacuum system from the pump itself. This review deals exclusively with contamination which can be attributed to backstreaming of diffusion pump working fluid. It discusses the origins of this type of contamination, survey methods used to prevent and control it and shows that it is possible to produce a clean vacuum using such pumps. N S Harris, Vacuum, 27 (9), 1977,519-530. 22. GAUGES
AND
MEASUREMENT
OF LOW PRESSURES
22 3478. The design and study of a compact bakeable ultra-high vacuum system for calibrating absolutely low pressure gauges. (GB) .& compact stainless-steel &a-high vacuum system is designed, constructed and tested which enables anv vacuum gauge to be calibrated absolutely, quickly and reliably o;er the pressure range 10