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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic measurement of atomic hydrogen level populations and hydrogen dissociation degree in expanding cascaded arc plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4499-4510 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical absorption spectroscopy has been applied to measure the absolute population densities of the first excited levels of atomic hydrogen H*(n=2) and argon Ar*(4s) in an expanding cascaded arc plasma in hydrogen-argon mixture. It is demonstrated that the method allows us to determine both H*(n=2) and Ar*(4s) absolute density radial profiles for H2 admixtures in Ar ranging from 0.7% to 10% with good accuracy. The measured H*(n=2) densities are in the 1014–1016 m−3 range, and Ar*(4s) densities are in the range of 1015–1018 m−3. It has been shown, that the density of hydrogen excited atoms H*(n=2) serves as an indicator of the presence of argon ions and hydrogen molecules in the expanding plasma. A kinetic model is used to understand evolution of H*(n=2) density in the expansion, and to estimate the total atomic hydrogen population density and hydrogen dissociation degree in sub- and supersonic regions of the plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357281
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  • 2
    Electronic Resource
    Electronic Resource
    Fabry–Pérot line shape analysis on an expanding cascaded arc plasma in argon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2775-2780 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fabry–Pérot line profile measurements have been used to obtain heavy particle temperatures and electron densities for an expanding cascaded arc plasma in argon. This was done for the argon 415.9 and 696.5 nm neutral lines as a function of the distance from the onset of the expansion. Temperatures in the range of 2000–12 000 K were obtained. The electron density in the beginning of the expansion appeared to be 5.6×1021 m−3. The 696.5 nm line profiles appeared to be asymmetric because of self-absorption by cool metastables around the plasma. The density and temperature of these metastables could be determined by fitting the measurements to a theoretical model, and appeared to be around 1017 m−3 and around 3000 K, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356216
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  • 3
    Electronic Resource
    Electronic Resource
    Emission spectroscopy on a supersonically expanding argon/silane plasma (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4156-4163 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from emission spectroscopy measurements on an Ar/SiH4 plasma jet which is used for fast deposition of amorphous hydrogenated silicon are presented. The jet is produced by allowing a thermal cascaded arc plasma in argon (I=60 A, V=80 V, Ar flow=60 scc/s and pressure 4 × 104 Pa) to expand to a low pressure (100 Pa) background. In the resulting plasma SiH4 is injected in front of the stationary shock front. Assuming a partial local thermal equilibrium situation for higher excited atomic levels, emission spectroscopy methods yield electron densities (∼ 1018 m−3), electron temperatures (∼5000 K) as well as concentrations of H+, Si+, and Ar+ particles. The emission spectrum of the SiH radical, the A 2Δ–X 2Π electronic transition, is observed. Numerical simulations of this spectrum are performed, resulting in upper limits for the rotational and vibrational temperatures of 4000 and 5600 K, respectively. The results can be understood assuming that, in the expansion, charge exchange and dissociative recombination are dominant processes in the formation of species in excited states, notably Si+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350850
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  • 4
    Electronic Resource
    Electronic Resource
    Dissociative recombination in cascaded arc generated Ar–N2 and N2 expanding plasma (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2086-2095 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The expanding plasma obtained from a cascaded arc thermal source is analyzed with double probe, mass spectrometric, and Faraday cup measurements. In the argon–nitrogen mixtures a decrease in ion fluence is observed, contrary to pure argon plasmas in which recombination is insignificant. The recombination in argon–nitrogen plasmas is caused by charge exchange between atomic ions and N2 molecules followed by dissociative recombination. Hence, these processes account for the enhanced axial decay of the plasma density and also for the change in the ion mass spectra of the ion beam extracted from the expanding plasma. The total ion beam current density is also governed by charge exchange followed by dissociative recombination and is thus dependent on the recirculating neutral molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870604
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  • 5
    Electronic Resource
    Electronic Resource
    A two-dimensional nonequilibrium model of cascaded arc plasma flows (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2548-2557 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonequilibrium model is developed for the prediction of two-dimensional flow, electron and heavy particle temperatures, and number density distributions in cascaded arcs of monatomic gases. The system of strongly coupled elliptic partial differential equations describing plasma flow is solved by a numerical method based on a control volume with a nonstaggered numerical grid. The model is applied for the computation of both stagnation and flowing argon arc plasmas. The results show that the plasma in stagnation arcs is nearly in local thermal equilibrium (LTE), except very close to the wall, whereas fast flowing arc plasmas exhibit a significant degree of nonequilibrium, both close to the wall and in the inlet region. The results of the calculations are in satisfactory agreement with experimental data, both for the cases of stagnation and flowing argon cascaded arc plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859967
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  • 6
    Electronic Resource
    Electronic Resource
    A combined Thomson–Rayleigh scattering diagnostic using an intensified photodiode array (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3369-3377 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A combined Thomson–Rayleigh scattering device is discussed. It consists of a Nd:YAG laser as a light source in combination with a multichannel detection technique consisting of a gated light amplifier in combination with an optical multichannel analyzer. Special attention is focused on the analysis of the measured spectra. Including convolution methods and taking into account weak coherent effects increases the dynamic range and the accuracy of the measured electron density ne and temperature Te and neutral particle density n0. Accuracies of 1%–4% for ne, 2%–6% for Te, and 10%–50% for n0 depending on the plasma condition are obtained. The dynamic range for ne is 7×1017–1021 m−3, for n0 is 1020–1023 m−3 and for Te is 1000–50 000 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142554
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  • 7
    Electronic Resource
    Electronic Resource
    Experimental characterization of a hydrogen/argon cascaded arc plasma source : Proceedings of 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1469-1471 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A H2 /Ar cascaded arc plasma source has been experimentally characterized by determination of the efficiency, the electric field, and the pressure gradient of the arc. The results show that the efficiency of a H2/Ar cascaded arc drops when the hydrogen flow rate is increased. The electron temperature in the argon cascaded arc has been derived to be in the range 9000–12 500 K. For a hydrogen arc, the mass dissociation degree of hydrogen molecules has been derived to be above 60%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144949
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  • 8
    Electronic Resource
    Electronic Resource
    Visible light tomography using an optical imaging system : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5185-5187 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A system for tomography in the wavelength range 200–1100 nm has been designed for the Rijnhuizen Tokamak Project (RTP). The plasma is viewed from five directions in one poloidal plane with a total of 80 detectors. An optical imaging system consisting of two spherical mirrors for each viewing direction is used to combine a good spatial resolution (1 cm, the minor radius of RTP being 17 cm) with a sufficiently high signal level for the fast electronics (200 kHz). Because of the complexity of the imaging, implementation of the system into common tomography codes is not straightforward. Ray tracing is used to calculate the contribution of the local emissivities in the plasma to the measured signals of the various detectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143424
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  • 9
    Electronic Resource
    Electronic Resource
    The meiobenthos of five mangrove vegetation types in Gazi Bay, Kenya (1992)
    Springer
    Hydrobiologia 247 (1992), S. 99-108 
    Details
    ISSN: 1573-5117
    Keywords: meiobenthos ; mangroves ; distribution ; Kenya
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The vertical distribution of meiofauna in the sediments ofAvicennia marina,Bruguiera gymnorrhiza,Ceriops tagal,Rhizophora mucronata andSonneratia alba at Gazi Bay (Kenya), is described. Seventeen taxa were observed, with highest densities in the sediments ofBruguiera (6707 ind. 10 cm−2), followed byRhizophora (3998 ind. 10 cm−2),Avicennia (3442 ind. 10 cm−2),Sonneratia (2889 ind. 10 cm−2) andCeriops (1976 ind. 10 cm−2). Nematodes accounted for up to 95% of total densities; other common taxa were copepods, turbellarians, oligochaetes, polychaetes, ostracods and rotifers. High densities occurred to about 20 cm depth in the sediment. EspeciallyCeriops sediments show still high densities of nematodes (342 ind. 10 cm−2) and copepods (11 ind. 10 cm−2) in the deepest layer (15–22 cm). Particle size and oxygen conditions were major factors influencing meiobenthic distribution;Uca burrows had a major impact on distribution and abundance of meiofauna.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008208
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  • 10
    Electronic Resource
    Electronic Resource
    Description of a flowing cascade arc plasma (1990)
    Springer
    Plasma chemistry and plasma processing 10 (1990), S. 531-551 
    Details
    ISSN: 1572-8986
    Keywords: Cascade arcs ; flowing plasmas ; nonequilibrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The plasma in a cascaded arc in argon with flow is studied both experimentally and theoretically. The plasma pressure has been measured as a function of axial position in the are channel with a Baratron pressure transducer. The electron density and the electron temperature have been determined as a function of axial position using Hβ-Stark broadening and line-continuum emissivity ratio, respectively. Comparison of the gas pressure measurements with an equilibrium model suggests that the /low is laminar. A one-dimensional nonequilibrium model based on the electron- and heavy-particle number balances and the heavy-particle energy balance is presented. The measured axial profiles of the electron density agree well with the model predictions, especially in the most upstream part of the arc channel. The plasma is strongly ionizing. Temperature equilibration takes about 20 mm of arc length, depending on the argon flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01447263
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