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4068. Two modes of moving striations in neon glow discharges. (GB)
Classified
abstracts
4063-4073
or somewhat higher. The dominant influence of the electric field on the electron emission is established. This result is in agreement with the total ion mass produced by Joule heating in the cathode as has been previously calculated for the same range of metals. (Netherlands) J E Daalder, JPhys D: Appl Phys, 11 (12), 1978, 1667-1682.
._ IL
4063. Time-resolved studies of the electrical breakdown of a gas at radio frequencies. (GB) The electrical breakdown of a gas at radio frequencies in the hf band (f-10 MHz) has been studied in some detail over a period of about 10 cycles of the applied field immediately prior to and following a breakdown event. Discharge current and voltages are monitored as a function of time, together with the photon output from electronically excited species in the gas. The development of the discharge over the first few cycles of the applied field following initiation of the discharge is determined by parameters such as overvoltage and the dynamic properties of the radio frequency generator. These two properties in particular control to a large extent the early breakdown phase. (Australia) S C Haydon and I C Plumb, J Phys D: Appl Phys, 11 (12), 1978, 1721-1730. 12 4064. Boltzmann equation analysis of the electron swarm development in nitrogen. (GB) The electron swarm development in nitrogen is studied for EN values from 56.6 to 1131 Td (E/p,, = 20-400 V cm-’ torr-’ at 0°C) by a Boltzmann equation method in which the etTect of ionisation is considered properly. Alteration of the electron collision crosssections from the literature is limited to a minimum, although minor amendments are found necessary for the ionisation coefficient to agree well with previous measurements. The cross-sections for vibrational excitation are considered separately for its quantum number c = I-10. The electron swarm parameters are calculated for the time-of-flight, pulsed Townsend and steady-state Townsend experiments. The results show that the deducted electron drift velocity, diffusion coefficient and mean energy are generally in good agreement with previous experimental and theoretical values and that the value of a swarm parameter should depend on the type of experiment at high E/N in nitrogen, the same as suggested with argon by Tagashira et al in 1977. The electron energy distribution, excitation frequencies to the vibrational and electronic levels, electron energy loss factor and percentage energy loss are also calculated and discussed. (Japan) T Taniguchi et al, J Phys D: Appl Phys, 11 (12), 1978, 1757-1768.
4065. The transition from the first to the second stage of the ring discharge. (GB) The circumferential component of electric field EO required to initiate the transition from the first to the second stage of the ring discharge was measured in the pressure range 10e3-1 torr in hydrogen while the field frequency was varied between 3 and 20 MHz. It was found that EO decreased with the increase in p. reached a minimum and then increased with the further increase in p. EO also increased with the increase in J However, at higher p the influence of .f on 6 was less noticeable. At lower ,fand lower p when the wall collisions were the dominant factor, no discharge could be produced. These observations are explained in simple physical terms. K Chandrakar, JPhys D: Applfhys, 11 (l3), 1978, 1809-1813. I2 4066. The motion of a low-pressure arc in a strong magnetic field. (GB) A low-pressure arc between copper electrodes has been driven by a transverse magnetic field of up to 5 T. At low field the arc moves in the retrograde direction, but above about I T the motion changes to the amperian direction. This result is consistent with the theory of retrograde motion proposed by Robson and von Engel. (USA) A E Robson, JPhys D: ApplPhys, 11 (l3), 1978, 1917-1923. 12 4067. Measurement of the traverse diffusion and Townsend’s first ionisation coefficients from the observation of the photon flux produced in a Townsend discharge in molecular hydrogen. (GB) The method used to obtain the transport parameters of a Townsend discharge reported by Blevin et al in 1976 from the observation of the photon flux produced in the discharge has been extended to enable measurements of the transverse diffusion coefficient and Townsend’s 324
first ionisation to be made. The results obtained in molecular hydrogen are reported in this paper. (Australia) H A Blevin et al, J Phys D: Appl Phys, 11 (16), 1978, 2295-2303. 4068. Two modes of moving striations in neon glow discharges. (Gg) Three kinds of moving striations, calledp, r and s waves, are known to be excited at low discharge current in positive columns of glow discharges in neon gas. The dispersion relation for r and p weaves numerically calculated from the basic equations, which are modified from Wojaczek’s ones to include the metastable atoms, agree fairly well with the experimental results. The frequency of the r wave decreases with increase in the discharge current, while that of the p increases. The frequency dependence of the gas pressure for both waves is inverse. The calculated gas temperature dependence of the frequency for both waves also agrees well with the experimental values for gas temperatures from 80 to 250 K. (Japan) K Ohe and S Takeda, J Phys D: Appl Phys, 11 (16), 1978,2257-2265. 12 4069. Observation of high-temperature electron injection in dense argon and mercury: application to cathode spots. (GB) The author presents experimental results which show that a wall in contact with a dense hot metal vapour injects a very-high-density current. In the same way, at the root of a cathode spot the vapour density is very high and a calculation is made of the enhancement of the electron emission due to the lowering of the work-function caused by the polarization energy of the excess electrons in the vapour. A relation is established which allows the density of the vapour to be determined and, thus, the rate of evaporation of a cathode made out of any material. Reasonable agreement is found with experiments. (France) A Leycuras, J Phys D: Appl Phgs, 11 (l6), 1978, 2249-2256. 4070. The spatial and temporal development of the early phases b’f homogeneous discharges in N,. (GB) The spatiotemporal development of electron densities within homogeneous overvolted discharges in Nz is investigated by optical means during the early build-up phases. The use of photomultiplier techniques rather than image devices enables a quantitative comparison between experiment and one-dimensional model calculations. The influences of space-charge fields and photosuccessors on discharge development are investigated. Considerable electron densities are also detected in front of the primary avalanche even during the early, field-distortion-free stages of the development. Their distribution can be described by a two-component gas photoionisation model. (Germany) 0 R Ahrens, .I Ph.tl.7 D: ApplPhys, 11 (l6), 1978, 2175-2184.
II. Vacuum 21. PUMPS
AND
4071. Capabilities liquid ring pumps. This paper covers ejectors and liquid of operation. B Ebdale, Vac~nr,
apparatus PUMP
and auxiliaries
FLUIDS
21 and limitations of pumps. Steam jet ejectors and (GB) two distinct types of vacuum producing pumpsring pumps, which completely differ in their mode 28 (8:9), 1978, 337-341.
21 4072. Rotary pump back-migration. (GB) This review deals exclusively with vacuum system contamination which can be attributed to back-migration of rotary pump working fluid. It discusses the origins of this type of contamination and survey methods used to prevent and control it. N S Harris, Vacul~m, 28 (67), 1978, 261-268.
Ill.
Vacuum
30. EVAPORATION
applications AND
DEPOSITION
IN VAC(I0
30 4073. Controlled vapour growth of small particles of Pd and Fe on thin A1203 substrates. (USA) An exploratory study, dealing with the preparation of well-defined particulate metal deposits that can be used in model studies of
abstracts
4063-4073
or somewhat higher. The dominant influence of the electric field on the electron emission is established. This result is in agreement with the total ion mass produced by Joule heating in the cathode as has been previously calculated for the same range of metals. (Netherlands) J E Daalder, JPhys D: Appl Phys, 11 (12), 1978, 1667-1682.
._ IL
4063. Time-resolved studies of the electrical breakdown of a gas at radio frequencies. (GB) The electrical breakdown of a gas at radio frequencies in the hf band (f-10 MHz) has been studied in some detail over a period of about 10 cycles of the applied field immediately prior to and following a breakdown event. Discharge current and voltages are monitored as a function of time, together with the photon output from electronically excited species in the gas. The development of the discharge over the first few cycles of the applied field following initiation of the discharge is determined by parameters such as overvoltage and the dynamic properties of the radio frequency generator. These two properties in particular control to a large extent the early breakdown phase. (Australia) S C Haydon and I C Plumb, J Phys D: Appl Phys, 11 (12), 1978, 1721-1730. 12 4064. Boltzmann equation analysis of the electron swarm development in nitrogen. (GB) The electron swarm development in nitrogen is studied for EN values from 56.6 to 1131 Td (E/p,, = 20-400 V cm-’ torr-’ at 0°C) by a Boltzmann equation method in which the etTect of ionisation is considered properly. Alteration of the electron collision crosssections from the literature is limited to a minimum, although minor amendments are found necessary for the ionisation coefficient to agree well with previous measurements. The cross-sections for vibrational excitation are considered separately for its quantum number c = I-10. The electron swarm parameters are calculated for the time-of-flight, pulsed Townsend and steady-state Townsend experiments. The results show that the deducted electron drift velocity, diffusion coefficient and mean energy are generally in good agreement with previous experimental and theoretical values and that the value of a swarm parameter should depend on the type of experiment at high E/N in nitrogen, the same as suggested with argon by Tagashira et al in 1977. The electron energy distribution, excitation frequencies to the vibrational and electronic levels, electron energy loss factor and percentage energy loss are also calculated and discussed. (Japan) T Taniguchi et al, J Phys D: Appl Phys, 11 (12), 1978, 1757-1768.
4065. The transition from the first to the second stage of the ring discharge. (GB) The circumferential component of electric field EO required to initiate the transition from the first to the second stage of the ring discharge was measured in the pressure range 10e3-1 torr in hydrogen while the field frequency was varied between 3 and 20 MHz. It was found that EO decreased with the increase in p. reached a minimum and then increased with the further increase in p. EO also increased with the increase in J However, at higher p the influence of .f on 6 was less noticeable. At lower ,fand lower p when the wall collisions were the dominant factor, no discharge could be produced. These observations are explained in simple physical terms. K Chandrakar, JPhys D: Applfhys, 11 (l3), 1978, 1809-1813. I2 4066. The motion of a low-pressure arc in a strong magnetic field. (GB) A low-pressure arc between copper electrodes has been driven by a transverse magnetic field of up to 5 T. At low field the arc moves in the retrograde direction, but above about I T the motion changes to the amperian direction. This result is consistent with the theory of retrograde motion proposed by Robson and von Engel. (USA) A E Robson, JPhys D: ApplPhys, 11 (l3), 1978, 1917-1923. 12 4067. Measurement of the traverse diffusion and Townsend’s first ionisation coefficients from the observation of the photon flux produced in a Townsend discharge in molecular hydrogen. (GB) The method used to obtain the transport parameters of a Townsend discharge reported by Blevin et al in 1976 from the observation of the photon flux produced in the discharge has been extended to enable measurements of the transverse diffusion coefficient and Townsend’s 324
first ionisation to be made. The results obtained in molecular hydrogen are reported in this paper. (Australia) H A Blevin et al, J Phys D: Appl Phys, 11 (16), 1978, 2295-2303. 4068. Two modes of moving striations in neon glow discharges. (Gg) Three kinds of moving striations, calledp, r and s waves, are known to be excited at low discharge current in positive columns of glow discharges in neon gas. The dispersion relation for r and p weaves numerically calculated from the basic equations, which are modified from Wojaczek’s ones to include the metastable atoms, agree fairly well with the experimental results. The frequency of the r wave decreases with increase in the discharge current, while that of the p increases. The frequency dependence of the gas pressure for both waves is inverse. The calculated gas temperature dependence of the frequency for both waves also agrees well with the experimental values for gas temperatures from 80 to 250 K. (Japan) K Ohe and S Takeda, J Phys D: Appl Phys, 11 (16), 1978,2257-2265. 12 4069. Observation of high-temperature electron injection in dense argon and mercury: application to cathode spots. (GB) The author presents experimental results which show that a wall in contact with a dense hot metal vapour injects a very-high-density current. In the same way, at the root of a cathode spot the vapour density is very high and a calculation is made of the enhancement of the electron emission due to the lowering of the work-function caused by the polarization energy of the excess electrons in the vapour. A relation is established which allows the density of the vapour to be determined and, thus, the rate of evaporation of a cathode made out of any material. Reasonable agreement is found with experiments. (France) A Leycuras, J Phys D: Appl Phgs, 11 (l6), 1978, 2249-2256. 4070. The spatial and temporal development of the early phases b’f homogeneous discharges in N,. (GB) The spatiotemporal development of electron densities within homogeneous overvolted discharges in Nz is investigated by optical means during the early build-up phases. The use of photomultiplier techniques rather than image devices enables a quantitative comparison between experiment and one-dimensional model calculations. The influences of space-charge fields and photosuccessors on discharge development are investigated. Considerable electron densities are also detected in front of the primary avalanche even during the early, field-distortion-free stages of the development. Their distribution can be described by a two-component gas photoionisation model. (Germany) 0 R Ahrens, .I Ph.tl.7 D: ApplPhys, 11 (l6), 1978, 2175-2184.
II. Vacuum 21. PUMPS
AND
4071. Capabilities liquid ring pumps. This paper covers ejectors and liquid of operation. B Ebdale, Vac~nr,
apparatus PUMP
and auxiliaries
FLUIDS
21 and limitations of pumps. Steam jet ejectors and (GB) two distinct types of vacuum producing pumpsring pumps, which completely differ in their mode 28 (8:9), 1978, 337-341.
21 4072. Rotary pump back-migration. (GB) This review deals exclusively with vacuum system contamination which can be attributed to back-migration of rotary pump working fluid. It discusses the origins of this type of contamination and survey methods used to prevent and control it. N S Harris, Vacul~m, 28 (67), 1978, 261-268.
Ill.
Vacuum
30. EVAPORATION
applications AND
DEPOSITION
IN VAC(I0
30 4073. Controlled vapour growth of small particles of Pd and Fe on thin A1203 substrates. (USA) An exploratory study, dealing with the preparation of well-defined particulate metal deposits that can be used in model studies of