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947. A high-vacuum sorption pump
Classified abstracts
940-948
the discharge. Using this relaxation constant and known excitation cross sections, a comprehensive picture of the kinetics of the CO,-He laser has been obtained. This approach does not require knowleged of the electron energy distribution function. Populations and temperatures of different vibrational levels have been calculated, as well as energy transfer rates to these levels. Quantitative results are presented and compared with otherwise known data on small-signal gain and energy transfer rates.
values obtained from magnetic probe data. These measurements gave the dependence I, CCt-o,66, which was weaker than the dependences predicted by theories based on neutral depletion (1-314), pressure balance (t- ‘), magnetically reduced conductivity (t- I) and wall evaporation (teZ). Moreover, all of these theories gave numerical values of I, that were very different from the measured times. C B Wheeler, J Phys D: Appl Phys 7, (2), 1974, 363-368.
L Friedland et al, J Phys D: Appl Phys, 7 (2), 1974, 303-313.
18 944. Microwave radiometric investigation of the positive column instability in pulsed nitrogen discharges. (USA) A microwave radiometric technique has been used to study the
940. Dissociation (CB)
mechanism
in pulsed and continuous
CO,
18 lasers.
The dissociation of carbon dioxide in the positive column of a glow discharge has been measured in CO, and in C02-Nz and CO1N2-He mixtures as used in low-pressure (l-20 torr) gas lasers. Both for continuous and pulsed discharges the measured dissociation rate is proportional to the electron density. The dissociation cofficient increases with the reduced field strength E/p, but for a given E/p it is very much greater for C02-N,-He than for C02-NZ, and is greater for COZ-N, than for CO,. This variation is consistent with the variation of the electron energy distribution and drift velocity with the different gases, and it is not necessary to postulate more than one dissociation mechanism. A L S Smith and J M Austin, J Phys D: Appl Phys, 7 (2), 1974, 314-322. 18 941. Increased efficiency and new CW transitions in the helium-iodine laser system. (GB)
Continuous-wave laser oscillation on transitions of singly ionized iodine has been obtained at increased laser efficiency in heliumiodine gas mixtures using a narrow-bore (3 mm), multiple-anode/ hollow-cathode laser tube. The sixteen CW laser lines observed include among their number six which have not formerly been reported as oscillating on a CW basis. Output characteristics of the laser as a function of helium pressure, iodine partial pressure and discharge current have been studied. The output intensity for all lines rises linearly for increasing discharge current beyond threshold to the limit of currents investigated. J A Piper, J Phys D: Appl Phys, 7 (2), 1974,323-328. 942. Orifice probe for plasma diagnostics:
II. Multi-parameter
18 analysis.
(Canada) A multi-grid orifice probe and analysis technique are presented which permit the measurement of the following plasma parameters: the electron number density a., the electron temperature T., the space potential V., and an estimate of the metastable number density n,. Simultaneously, the analysis allows the quantitative determination of instrumental parameters such as the reflection coefficient for slow (~30 eV) electrons from the grids R,(G) and roughened (gold-black) collector’R.(C), the secondary electron. emission-coefficient for fast (>30 eV) electrons y.(G) from the grids, and the effective transparencies of the grids for electrons T.(G), and for metastable T,(G). Experimental ion, electron and total current characteristics are presented for a low-pressure (1.8 x 10m2 torr) RF discharge in argon. The major part of the analysis method involves the use of ten ‘plateau values’ obtained from the characteristics to determine values for most of these parameters. T, and V, are determined separately. The values obtained are: n. = 2.74 x lo9 cme3 & 18 ‘A, kT, = 1.92 eV f 5%, V, = 11.7 f 0.1 V, n, N 3.3 x lo9 cmm3 + 50x, R,(G) = 0.65 f 0.10, R,(C) = 0.22 & 0.10, y.(G) = 0.935 ic 0.010, T,(G) = 0.830 & 0.002, and r,,,(G) = 0.850 f 0.002. The transparencies r,(G) and r,(G) are within 4% of the geometrical transparency T(G) = 0.860. Approximately equal numbers of atoms (I in 2 x 105) are in metastable and ionized states. S M L Prokopenko et al, J Phys D: Appl Phys, 7 (2), 1974, 355-362. 943. Measurement (GB)
18 of wall bang-up time for the linear pinched discharge.
Measurements were carried out on a slow linear pinch in argon using rates of current rise f between IO* and 10”’ A s-‘. Determination of the wall hang-up time t, by comparison of the measured time to pinch with theoretical collapse models gave values that strongly disagreed with estimates obtained from image converter observation. However, the duration of the initial plateau in the tube voltage waveform yielded values of f, that were in excellent agreement with 320
positive column instability in pulsed nitrogen discharges. The technique involves monitoring the effective temperature of microwave radiation as a function of the longitudinal magnetic field. The critical magnetic field B, for the onset of the instability is found to be dependent on both the discharge current and the duration of the excitation pulse. The experimental results are consistent with an explanation based on significant cumulative ionization. The plasma became turbulent at progressively lower values of magnetic field above B, as the discharge current was increased. Further increase in current led to the unstable regime beyond B, reverting back to stability on progressively increasing the magnetic field. Omesb Sabni and W C Jennings, J Phys D: Appl Phys, 7 (2), 1974, 369-373. 945. Microwave
18 multiple-pulse
breakdown
in nitric oxide. (Norway)
The minimum value of the peak RMS electric field for the TE, I mode resulting in the breakdown of pure nitric oxide has been measured in the pressure range 0.5-10 torr. The microwave frequency was 9.361 GHz. For each pressure selected, the breakdown formation time 7 was found as a function of the electric field. For all breakdown formation times, the minimum breakdown field occurred at a pressure of 34 torr, the pulse repetition frequency and pulse length being 100 pps and 4.7 ms respectively. M Mentzoni, J Phys D : Appl Phys, 7 (2), 1974,374-377. 946. The limiting condition negative ions. (GB)
for sparkover
18 in gases forming unstable
The theory predicting the limiting E/p (electric field strength/gas pressure), below which uniform-field breakdown is not possible, is extended to cover those electro-negative gases where unstable negative ions are effective. The result is consistent with the experimental results of other authors in oxygen. It is shown that in general at the limiting E/p the growth of current with distance is not linear, in contrast to the case where only stable negative ions are formed. D T A Blair and B H Cricbton, J Phys D: Appl Phys, 7 (2), 1974, 378-382.
II. Vacuum 21. PUMPS
apparatus
and auxiliaries
AND PUMP FLUIDS
947. A high-vacuum sorption pump. (USSR) A method of preventing the accumulation of oxide films on the getters of sorption pumps operating under leak conditions is described. The sorbing element is made of a sorption-active metal such as niobium and differs from existing models in that this element is made in the form of a hermetic hollow vessel containing an alkali metal such as lithium in order to remove oxygen from the sorbing metal. The pump is first evacuated to IO-“ torr and the sorbing element is then heated to 1000°C; the pump is thereby enabled to evacuate the attached system to lo- ” torr. Best results are obtained in evacuating oxygen and oxygen-containing gases. E N Martinson et al, Soviet Patent, class F 04 b, 37103, No 355, 38 I, claimed 2517169, published 1/I l/72 (in Russian). 21 948. A magnetic discharge evacuation
system. (USSR)
A new design of anode for magnetic discharge pumps is described. The orthogonal faces of the anode cells are made of different heights in accordance with a strictly specified geometry relative to the cathode. The effect of this construction is that of retaining electron clouds favourably oriented with respect to the magnetic field inside
940-948
the discharge. Using this relaxation constant and known excitation cross sections, a comprehensive picture of the kinetics of the CO,-He laser has been obtained. This approach does not require knowleged of the electron energy distribution function. Populations and temperatures of different vibrational levels have been calculated, as well as energy transfer rates to these levels. Quantitative results are presented and compared with otherwise known data on small-signal gain and energy transfer rates.
values obtained from magnetic probe data. These measurements gave the dependence I, CCt-o,66, which was weaker than the dependences predicted by theories based on neutral depletion (1-314), pressure balance (t- ‘), magnetically reduced conductivity (t- I) and wall evaporation (teZ). Moreover, all of these theories gave numerical values of I, that were very different from the measured times. C B Wheeler, J Phys D: Appl Phys 7, (2), 1974, 363-368.
L Friedland et al, J Phys D: Appl Phys, 7 (2), 1974, 303-313.
18 944. Microwave radiometric investigation of the positive column instability in pulsed nitrogen discharges. (USA) A microwave radiometric technique has been used to study the
940. Dissociation (CB)
mechanism
in pulsed and continuous
CO,
18 lasers.
The dissociation of carbon dioxide in the positive column of a glow discharge has been measured in CO, and in C02-Nz and CO1N2-He mixtures as used in low-pressure (l-20 torr) gas lasers. Both for continuous and pulsed discharges the measured dissociation rate is proportional to the electron density. The dissociation cofficient increases with the reduced field strength E/p, but for a given E/p it is very much greater for C02-N,-He than for C02-NZ, and is greater for COZ-N, than for CO,. This variation is consistent with the variation of the electron energy distribution and drift velocity with the different gases, and it is not necessary to postulate more than one dissociation mechanism. A L S Smith and J M Austin, J Phys D: Appl Phys, 7 (2), 1974, 314-322. 18 941. Increased efficiency and new CW transitions in the helium-iodine laser system. (GB)
Continuous-wave laser oscillation on transitions of singly ionized iodine has been obtained at increased laser efficiency in heliumiodine gas mixtures using a narrow-bore (3 mm), multiple-anode/ hollow-cathode laser tube. The sixteen CW laser lines observed include among their number six which have not formerly been reported as oscillating on a CW basis. Output characteristics of the laser as a function of helium pressure, iodine partial pressure and discharge current have been studied. The output intensity for all lines rises linearly for increasing discharge current beyond threshold to the limit of currents investigated. J A Piper, J Phys D: Appl Phys, 7 (2), 1974,323-328. 942. Orifice probe for plasma diagnostics:
II. Multi-parameter
18 analysis.
(Canada) A multi-grid orifice probe and analysis technique are presented which permit the measurement of the following plasma parameters: the electron number density a., the electron temperature T., the space potential V., and an estimate of the metastable number density n,. Simultaneously, the analysis allows the quantitative determination of instrumental parameters such as the reflection coefficient for slow (~30 eV) electrons from the grids R,(G) and roughened (gold-black) collector’R.(C), the secondary electron. emission-coefficient for fast (>30 eV) electrons y.(G) from the grids, and the effective transparencies of the grids for electrons T.(G), and for metastable T,(G). Experimental ion, electron and total current characteristics are presented for a low-pressure (1.8 x 10m2 torr) RF discharge in argon. The major part of the analysis method involves the use of ten ‘plateau values’ obtained from the characteristics to determine values for most of these parameters. T, and V, are determined separately. The values obtained are: n. = 2.74 x lo9 cme3 & 18 ‘A, kT, = 1.92 eV f 5%, V, = 11.7 f 0.1 V, n, N 3.3 x lo9 cmm3 + 50x, R,(G) = 0.65 f 0.10, R,(C) = 0.22 & 0.10, y.(G) = 0.935 ic 0.010, T,(G) = 0.830 & 0.002, and r,,,(G) = 0.850 f 0.002. The transparencies r,(G) and r,(G) are within 4% of the geometrical transparency T(G) = 0.860. Approximately equal numbers of atoms (I in 2 x 105) are in metastable and ionized states. S M L Prokopenko et al, J Phys D: Appl Phys, 7 (2), 1974, 355-362. 943. Measurement (GB)
18 of wall bang-up time for the linear pinched discharge.
Measurements were carried out on a slow linear pinch in argon using rates of current rise f between IO* and 10”’ A s-‘. Determination of the wall hang-up time t, by comparison of the measured time to pinch with theoretical collapse models gave values that strongly disagreed with estimates obtained from image converter observation. However, the duration of the initial plateau in the tube voltage waveform yielded values of f, that were in excellent agreement with 320
positive column instability in pulsed nitrogen discharges. The technique involves monitoring the effective temperature of microwave radiation as a function of the longitudinal magnetic field. The critical magnetic field B, for the onset of the instability is found to be dependent on both the discharge current and the duration of the excitation pulse. The experimental results are consistent with an explanation based on significant cumulative ionization. The plasma became turbulent at progressively lower values of magnetic field above B, as the discharge current was increased. Further increase in current led to the unstable regime beyond B, reverting back to stability on progressively increasing the magnetic field. Omesb Sabni and W C Jennings, J Phys D: Appl Phys, 7 (2), 1974, 369-373. 945. Microwave
18 multiple-pulse
breakdown
in nitric oxide. (Norway)
The minimum value of the peak RMS electric field for the TE, I mode resulting in the breakdown of pure nitric oxide has been measured in the pressure range 0.5-10 torr. The microwave frequency was 9.361 GHz. For each pressure selected, the breakdown formation time 7 was found as a function of the electric field. For all breakdown formation times, the minimum breakdown field occurred at a pressure of 34 torr, the pulse repetition frequency and pulse length being 100 pps and 4.7 ms respectively. M Mentzoni, J Phys D : Appl Phys, 7 (2), 1974,374-377. 946. The limiting condition negative ions. (GB)
for sparkover
18 in gases forming unstable
The theory predicting the limiting E/p (electric field strength/gas pressure), below which uniform-field breakdown is not possible, is extended to cover those electro-negative gases where unstable negative ions are effective. The result is consistent with the experimental results of other authors in oxygen. It is shown that in general at the limiting E/p the growth of current with distance is not linear, in contrast to the case where only stable negative ions are formed. D T A Blair and B H Cricbton, J Phys D: Appl Phys, 7 (2), 1974, 378-382.
II. Vacuum 21. PUMPS
apparatus
and auxiliaries
AND PUMP FLUIDS
947. A high-vacuum sorption pump. (USSR) A method of preventing the accumulation of oxide films on the getters of sorption pumps operating under leak conditions is described. The sorbing element is made of a sorption-active metal such as niobium and differs from existing models in that this element is made in the form of a hermetic hollow vessel containing an alkali metal such as lithium in order to remove oxygen from the sorbing metal. The pump is first evacuated to IO-“ torr and the sorbing element is then heated to 1000°C; the pump is thereby enabled to evacuate the attached system to lo- ” torr. Best results are obtained in evacuating oxygen and oxygen-containing gases. E N Martinson et al, Soviet Patent, class F 04 b, 37103, No 355, 38 I, claimed 2517169, published 1/I l/72 (in Russian). 21 948. A magnetic discharge evacuation
system. (USSR)
A new design of anode for magnetic discharge pumps is described. The orthogonal faces of the anode cells are made of different heights in accordance with a strictly specified geometry relative to the cathode. The effect of this construction is that of retaining electron clouds favourably oriented with respect to the magnetic field inside