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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5254-5262 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spatial growth of ionization currents has been measured in CCl2F2/N2 mixtures by the steady-state Townsend method over the range of reduced fields 80 ≤E/p20≤180 V cm−1 Torr−1. The experimental values obtained differ markedly from those published in the literature. A detailed account of the various hypotheses used in the experiment is presented in the light of correspondence with the electron transport theory and is followed by a comparison of experimental data, i.e., limit fields (E/p20)*, ionization (α), attachment (η), and effective ionization (α¯) coefficients, with available theoretical values from Boltzmann-equation analysis of electron swarms in the pure gas and its mixture with N2. Good agreement with the theoretical calculations by J. P. Novak and M. F. Fréchette [J. Appl. Phys. 57, 4368 (1985)] provides further supporting evidence for the applicability of these authors' proposed set of electron scattering cross sections and, in particular, favors the attachment cross sections reported by E. Illenberger, H.-U. Scheunemann, and H. Baumgärtel [Ber. Bunsenges. Phys. Chem. 82, 1154 (1978); Chem. Phys. 37, 21 (1979)].
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 552-558 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ionization and attachment coefficients for CCl2F2/SF6 mixtures were determined from measurements of prebreakdown ionization currents in a steady-state Townsend discharge at a pressure p25=4 Torr and temperature of 25 °C. The curves representing the ionization coefficient (α) for reduced fields in the range from 110 to 180 V cm−1 Torr−1 exhibit a small maximum at about 15% of CCl2F2, while those representing the attachment coefficient (η) flatten out between 0% and 50% CCl2F2 and decrease at higher partial densities. The limit field obtained using the condition α=η shows two extrema, i.e., a minimum at approximately 20% and a maximum at 75% of CCl2F2, while the curves obtained from the breakdown-potential measurements available in the literature show only a maximum, at roughly the same position. Theoretical values of the transport coefficients were obtained by numerically solving the Boltzmann equation using previously determined effective sets of electron collision cross sections [J. P. Novak and M. F. Fréchette, J. Appl. Phys. 55, 107 (1984); 57, 4368 (1985)]. The good agreement between the calculated and the experimental values provides supporting evidence for the applicability of the present calculation method and collisional cross sections to analyze electron swarms in the range of fields comparable in magnitude to the limit field.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 3684-3693 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Prebreakdown ionization currents have been measured in SF6/N2 and SF6/CCl2F2 mixtures and respective gases by the steady-state Townsend method over the range of reduced fields 70≤E/p20≤200 V cm−1 Torr−1. Relevant collisional processes to be included in the formulation of the current-growth equation are briefly reviewed; electron detachment was accordingly neglected in the present current-growth analysis. A numerical simulation has been carried out to quantify the errors expected when numerically retrieving the transport coefficients. A two-parameter model, for which the initial current I0 is considered known, is found to give the best performance. Nonlinear regression analysis using Marquardt's procedure is performed for evaluation of the ionization (α), attachment (η), and effective ionization (α¯) coefficients. The limit fields are obtained from the condition α¯(E/p*)=0. The coefficients for the respective gases compare well with available data in the literature with the exception of the attachment coefficient in SF6 which shows a more pronounced decrease than the general trend as E/p increases. In the case of SF6/N2 mixtures, good agreement is found for the effective ionization coefficients. The attachment coefficients do not saturate but rather increase with the SF6 partial density. In SF6/CCl2F2 mixtures, the variation of α¯ is found to be nonlinear with the percentage mixture ratio. The resulting limit field exhibits small positive and negative synergistic effects, 6% and 3%, respectively; at 25% SF6 content, the limit field is approximately 5% greater than that of pure CCl2F2. For SF6/N2 mixtures, however, the limit field never exceeds that of SF6.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2570-2575 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An effective set of collisional cross sections of c-C4F8 was determined by fitting the transport coefficients, i.e., drift velocity, diffusion, ionization, and attachment coefficients, to available experimental data. The best fit was obtained for the following values: a total momentum transfer cross section of 8×10−15 cm2 for electron energies of z≤4 eV dropping to 1.75×10−15 cm2 for z〉12 eV, a maximum vibrational cross section of 8×10−15 cm2 at 0.4 eV, and an excitation cross section of about 4×10−16 cm2 between 9 and 20 eV. Ionization and attachment cross sections based on measurements by M. V. Kurepa [Transactions of the 3rd Czechoslovak Conference on Electronics and Vacuum Physics (Academia, Prague, 1967), p. 107] were used; the ionization cross section was multiplied by a correction factor of 0.59, while the attachment cross sections were readjusted according to measurements by C. Lifshitz and R. Grajower [Int. J. Mass Spectrom. Ion Phys. 10, 25 (1972/73)] and I. Sauers, L. G. Christophorou, and J. G. Carter [J. Chem. Phys. 71, 3016 (1979)]. Calculations of the transport coefficients of N2-c-C4F8 mixtures were also performed.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4368-4376 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of effective electron collision cross sections, including momentum transfer, vibration, and electron excitation collisions has been determined for CCl2F2 gas: the momentum transfer is approximately 2×10−15 cm2 with the highest maximum about 4×10−15 at 6 eV, two vibrational maxima with thresholds of 0.11 and 0.14 eV are about 9 and 4 (10−16 cm2) at 0.2 and 0.25 eV and two excitation maxima with thresholds of 7.0 and 9.8 eV are 2.8 and 5.1 (10−16 cm2) at 11 and 18 eV, respectively. The calculated transport coefficients are in satisfactory agreement with measured values, except for the attachment coefficient, which is too high at low (below 90 V cm−1 Torr−1) and high (above 180 V cm−1 Torr−1) reduced fields. The possibility of comparison in the case of N2-CCl2F2 mixtures is limited and agreement is less satisfactory than in the case of pure CCl2F2. Deviations for medium fields are within about 30% for the D/μ ratio and ionization coefficients. The attachment coefficients agree well at high partial density of CCl2F2 (above approximately 50%) but the experimental values are much higher than predicted at low CCl2F2 content. Calculated values of the limit fields agree well with the values obtained from breakdown potential measurements available in the literature.
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Optics Communications 30 (1979), S. 79-82 
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Thermochimica Acta 171 (1990), S. 115-122 
    ISSN: 0040-6031
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Thermochimica Acta 126 (1988), S. 155-164 
    ISSN: 0040-6031
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Thermochimica Acta 176 (1991), S. 221-232 
    ISSN: 0040-6031
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Thermochimica Acta 127 (1988), S. 125-137 
    ISSN: 0040-6031
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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