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4055. Transmittance of cultured crystalline quartz in the vacuum ultraviolet before and after electron irradiation. (USA)
Classified Classified
abstracts
abstracts
4054-4062
4054-4137
on this page
Editor’s note The label immediately following the title of each item denotes country or origin of publication, that at the end of each abstract indicates country of origin of work (where known).
I. General engineering 12. GASEOUS
vacuum
science
and
12
and
4058. Multidipole plasma density. (USA) The primary-electron bias voltage and theneutral-pressuredependence of plasma density in a multidipole device are investigated. Experi-
ELECTRONICS 12
4054. High-power discharge in Na-Xe vapor. (USA) High-power (10-100 MW/l) pulsed discharges in Na-doped Xe vapour have been studied at Na densities of 1015-10’6 crnv3 and Xe densities of 10’9-10*0 cme3, as appropriate for excimer-laser use. Stable steady-state discharges are obtained for a number of microseconds in a small-volume cell, without use of preionization or sustainers. This stability is attributed to the observed positive V-l characteristic. Measured spectra are interpreted to yield Na excited-state densities, and the implications for a potential excimer laser are discussed. H L Rothwell et al, J uppl Phys, 49 (8), 1978, 43964400. 12 4055. Transmittance of cultured crystalline quartz in the vacuum ultraviolet before and after electron irradiation. (USA)
The transmittance of cultured crystalline quartz has been measured in the vacuum uv from 2000 8, to its cutoff wavelength. For most samples this cutoff wavelength is approximately 1450 A, but some samples had very low transmittances to wavelengths as long as 1600 A. Furthermore, in the spectral region from 1450 to 2000 A, all the samples had nonuniform transmittances as a function of position on the sample. Most of these nonuniformities are quite pronounced close to the cutoff wavelength but disappear or are very small at 2000 A. After irradiation with 1 MeV electrons, the transmittances of the good, fairly uniform, samples were practically unchanged. However, areas of some of the less uniform samples became quite black to the eye and practically nontransmitting in the vacuum uv. In most cases, blackened and nonblackened areas, on the same sample had quite sharp boundaries, on the order of 1 mm or less. The blackened areas had excess aluminum and alkali impurities as determined by paramagnetic electron resonance measurements. A short comparison is made between cultured crystalline quartz and various types of fused silica. G Hass and W R Hunter, Appl. Opt, 17 (15), 1978, 231%2315. 4056 CAMAC-controlled (CR)
system for the measurement
12 of ion mohilities.
An electronic measuring system to determine ion time-of-arrival spectra in drift tubes is described. The system consists of a CAMAC crate interfaced to a minicomputer. An instrument with a great adaptive power, wide range of acceptable drift times and very short dead time has been realised. The circuitry and computer program used to perform the measurement are described, as well as the performance of the system. (Belgium) D Nevejans et al, JPhys E: Sci Instrum, 11 (9), 1978, 955-959. 4057. A rotating-electrode system for improved spark source mass spectrometry. (GB)
reproducibility
in
A modified electrode configuration in a spark source mass spectrometer improves the reproducibility of analytical results. The system consists of vertically mounted cylindrical electrodes facing each other, one of which is rotating. No rotary feedthrough is needed as coupling between a small magnet inside the source and one (driven by a motor) outside allows rotation. Hence, the vacuum inside the source can be kept low (less than 10m6 Pa = 1Om8torr). Relative standard deviations do not exceed 6% for highly inhomogeneous powder mixtures. Moreover, higher and more stable transmissions are obtained, while short-circuiting between low-melting-point materials is greatly reduced. (Belgium) J Haemers, J Phys Ec Sci Instrum,
11 (9), 1978, 897-898.
mental data are described by a simple model which takes into account the production of multiple electron-ion pairs by each ionizing primary electron. A Lang and N Hershkowitz,
4059. Recombination (USA)
J uppf Phys, 49 (9), 1978,4707-4710.
effects in an expanding
laser-produced
12 plasma.
The expansion of a laser-produced Be plasma is studied by comparing hydrodynamical model calculations with experimentally measured distributions of each charge state as a function of energy. The plasma is generated with l-10 J 200 ps pulses from the LPARL Nd-glass laser facility and the distributions are obtained using a Thomson parabolic spectrograph. The hydrodynamic equations include fluxlimited thermal conductivity and collisional-radiative recombination and ionization. For the proper choice of the initial parameters, we obtain qualitative agreement between the model prediction and the experimentally measured distributions. G L Payne et al, .I uppl Phys, 49 (9), 1978,4688-4693. 12 4060. Negative work-function correction at a positively-charged surface. (CB) It is shown that if a very high positive electric field is present at a
metal surface then the dipole moments electrically induced in the surface atoms must give rise to a field-related negative work-function correction. At the high fields encountered at a field-ion emitter, approximately 50 V nm-‘, the correction may be several electronvolts or more. It is also suggested that, in consequence of the Hellman-Feynman theorem, a discrete-charge model may in principle be a better classical model for a positively charted surface than a representation in terms of a continuous positive charge distribution. R G Forhes,JPhys D: ApplPhys, 11 (14), 1978, Ll61-L164. 12 4061. The effect of non-uniformities on the measured transport parameters of electron swarms in hydrogen. (GB) Measurements of transport parameters of pulsed electron swarms moving through a low-pressure gas by observation of the photon flux resulting from electron-molecule collisions have been recently reported. One of the possible sources of error in this kind of experiment is the variation of mean electron energy through the swarm. This effect is considered here along with the resulting variation of ionisation and excitation frequency through the swarm. The validity of the experimental method is considered in the light of the above factors. (Australia) HA
Blevin et al,JPhys
D: ApplPhys,
11 (12), 1978, 1653-1665.
12 4062. A cathode spot model and its energy balance for metal vapour arcs. (GB)
A non-stationary cathode spot model is proposed which is based on an interpretation of experimental data recently obtained. The significance of ion mass generation by Joule heating and the separation of energy flows associated with electron and ion currents in thecathodespot are the main differences with other known cathode spot models. The ion energy balance at the metal-vacuum transition is evaluated quantitatively and applied to a calculation of the ion fraction in the cathode current. For a broad range of metals and independent of the electron emission mechanism, minimum and maximum ion current fractions are found of around 10 and 20x, respectively. By considering TF emission it is shown that the ion currents orientated from and towards the cathode have the same size, each being 10% of the arc current 323
abstracts
abstracts
4054-4062
4054-4137
on this page
Editor’s note The label immediately following the title of each item denotes country or origin of publication, that at the end of each abstract indicates country of origin of work (where known).
I. General engineering 12. GASEOUS
vacuum
science
and
12
and
4058. Multidipole plasma density. (USA) The primary-electron bias voltage and theneutral-pressuredependence of plasma density in a multidipole device are investigated. Experi-
ELECTRONICS 12
4054. High-power discharge in Na-Xe vapor. (USA) High-power (10-100 MW/l) pulsed discharges in Na-doped Xe vapour have been studied at Na densities of 1015-10’6 crnv3 and Xe densities of 10’9-10*0 cme3, as appropriate for excimer-laser use. Stable steady-state discharges are obtained for a number of microseconds in a small-volume cell, without use of preionization or sustainers. This stability is attributed to the observed positive V-l characteristic. Measured spectra are interpreted to yield Na excited-state densities, and the implications for a potential excimer laser are discussed. H L Rothwell et al, J uppl Phys, 49 (8), 1978, 43964400. 12 4055. Transmittance of cultured crystalline quartz in the vacuum ultraviolet before and after electron irradiation. (USA)
The transmittance of cultured crystalline quartz has been measured in the vacuum uv from 2000 8, to its cutoff wavelength. For most samples this cutoff wavelength is approximately 1450 A, but some samples had very low transmittances to wavelengths as long as 1600 A. Furthermore, in the spectral region from 1450 to 2000 A, all the samples had nonuniform transmittances as a function of position on the sample. Most of these nonuniformities are quite pronounced close to the cutoff wavelength but disappear or are very small at 2000 A. After irradiation with 1 MeV electrons, the transmittances of the good, fairly uniform, samples were practically unchanged. However, areas of some of the less uniform samples became quite black to the eye and practically nontransmitting in the vacuum uv. In most cases, blackened and nonblackened areas, on the same sample had quite sharp boundaries, on the order of 1 mm or less. The blackened areas had excess aluminum and alkali impurities as determined by paramagnetic electron resonance measurements. A short comparison is made between cultured crystalline quartz and various types of fused silica. G Hass and W R Hunter, Appl. Opt, 17 (15), 1978, 231%2315. 4056 CAMAC-controlled (CR)
system for the measurement
12 of ion mohilities.
An electronic measuring system to determine ion time-of-arrival spectra in drift tubes is described. The system consists of a CAMAC crate interfaced to a minicomputer. An instrument with a great adaptive power, wide range of acceptable drift times and very short dead time has been realised. The circuitry and computer program used to perform the measurement are described, as well as the performance of the system. (Belgium) D Nevejans et al, JPhys E: Sci Instrum, 11 (9), 1978, 955-959. 4057. A rotating-electrode system for improved spark source mass spectrometry. (GB)
reproducibility
in
A modified electrode configuration in a spark source mass spectrometer improves the reproducibility of analytical results. The system consists of vertically mounted cylindrical electrodes facing each other, one of which is rotating. No rotary feedthrough is needed as coupling between a small magnet inside the source and one (driven by a motor) outside allows rotation. Hence, the vacuum inside the source can be kept low (less than 10m6 Pa = 1Om8torr). Relative standard deviations do not exceed 6% for highly inhomogeneous powder mixtures. Moreover, higher and more stable transmissions are obtained, while short-circuiting between low-melting-point materials is greatly reduced. (Belgium) J Haemers, J Phys Ec Sci Instrum,
11 (9), 1978, 897-898.
mental data are described by a simple model which takes into account the production of multiple electron-ion pairs by each ionizing primary electron. A Lang and N Hershkowitz,
4059. Recombination (USA)
J uppf Phys, 49 (9), 1978,4707-4710.
effects in an expanding
laser-produced
12 plasma.
The expansion of a laser-produced Be plasma is studied by comparing hydrodynamical model calculations with experimentally measured distributions of each charge state as a function of energy. The plasma is generated with l-10 J 200 ps pulses from the LPARL Nd-glass laser facility and the distributions are obtained using a Thomson parabolic spectrograph. The hydrodynamic equations include fluxlimited thermal conductivity and collisional-radiative recombination and ionization. For the proper choice of the initial parameters, we obtain qualitative agreement between the model prediction and the experimentally measured distributions. G L Payne et al, .I uppl Phys, 49 (9), 1978,4688-4693. 12 4060. Negative work-function correction at a positively-charged surface. (CB) It is shown that if a very high positive electric field is present at a
metal surface then the dipole moments electrically induced in the surface atoms must give rise to a field-related negative work-function correction. At the high fields encountered at a field-ion emitter, approximately 50 V nm-‘, the correction may be several electronvolts or more. It is also suggested that, in consequence of the Hellman-Feynman theorem, a discrete-charge model may in principle be a better classical model for a positively charted surface than a representation in terms of a continuous positive charge distribution. R G Forhes,JPhys D: ApplPhys, 11 (14), 1978, Ll61-L164. 12 4061. The effect of non-uniformities on the measured transport parameters of electron swarms in hydrogen. (GB) Measurements of transport parameters of pulsed electron swarms moving through a low-pressure gas by observation of the photon flux resulting from electron-molecule collisions have been recently reported. One of the possible sources of error in this kind of experiment is the variation of mean electron energy through the swarm. This effect is considered here along with the resulting variation of ionisation and excitation frequency through the swarm. The validity of the experimental method is considered in the light of the above factors. (Australia) HA
Blevin et al,JPhys
D: ApplPhys,
11 (12), 1978, 1653-1665.
12 4062. A cathode spot model and its energy balance for metal vapour arcs. (GB)
A non-stationary cathode spot model is proposed which is based on an interpretation of experimental data recently obtained. The significance of ion mass generation by Joule heating and the separation of energy flows associated with electron and ion currents in thecathodespot are the main differences with other known cathode spot models. The ion energy balance at the metal-vacuum transition is evaluated quantitatively and applied to a calculation of the ion fraction in the cathode current. For a broad range of metals and independent of the electron emission mechanism, minimum and maximum ion current fractions are found of around 10 and 20x, respectively. By considering TF emission it is shown that the ion currents orientated from and towards the cathode have the same size, each being 10% of the arc current 323