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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 15-21 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured and report the total gas-number-density normalized effective ionization coefficient, α¯/N, as a function of the density-reduced electric field, E/N for Ar, CO2, CF4, the binary gas mixtures CF4:Ar (20:80), CO2:Ar(20:80), CO2:CH4(20:80) and for the ternary gas mixtures CO2:CF4:Ar (10:10:80) and H2O:CF4:Ar(2:18:80). We also report the limiting value, (E/N)lim of the above gaseous systems. A comparison of our results on the unitary gases shows good agreement with previous measurements. The results on the ternary mixtures show that the addition of CO2 or H2O to the binary gas mixture CF4:Ar lowers the electron energies and increases α¯/N(E/N).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4879-4891 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electron attachment rate constants ka for SF6 have been measured in dilute mixtures of SF6 in high pressure (〉1 atm) N2, Ar, and Xe buffer gases at room temperature (T≈300 K) over a wide E/N range (electric field strength to gas number density ratio), corresponding to mean electron energies 〈ε〉 from near thermal electron energies (≈0.04 eV) to 〈ε〉≈4.3 eV. Particular attention has been paid to the effects of space charge distortion, molecular impurities, and changes in the electron energy distribution function on the measured electron attachment rate constant values at the lower E/N values in these mixtures. The present measured thermal electron attachment rate constants in SF6/N2 and SF6/Xe gas mixtures are in excellent agreement with recent accurate measurements of these parameters in several SF6/buffer gas mixtures. At higher 〈ε〉 values, the present SF6/N2 measurements are in fair agreement with previous measurements, while no previous measurements using Ar and Xe buffer gases have been published. These measurements have been used in numerical two term, spherical harmonic Boltzmann equation analyses of the electron motion in these gas mixtures to obtain the low energy (〈10 eV) nondissociative and dissociative electron attachment cross sections for SF6. The present derived electron attachment cross sections are compared with recently measured and derived nondissociative and dissociative electron attachment cross sections for SF6. The primary value of the present results is in the large and overlapping 〈ε〉 ranges of the present ka measurements for the three buffer gases compared with that for SF6/N2 gas mixtures alone, which in turn, makes these measurements ideal for testing cross-section sets in SF6 for use in many applied studies.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9031-9035 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electron attachment rate constant ka(〈ε〉, T) for CH3Br has been measured in a buffer gas of N2 using a high pressure electron swarm apparatus, within the mean electron energy range from thermal (∼0.046 eV) to 0.87 eV and over the temperature range, T, 300–700 K. At room temperature, CH3Br attaches low energy electrons weakly but as T is raised from 300 to 700 K the total electron attachment cross section increases by more than 2 orders of magnitude. At T=300 K the electron attachment cross section exhibits a peak at 0.38 eV which shifts progressively to lower electron energies as T is increased. The thermal value of ka is 1.08×10−11 cm3 s−1 at 300 K and 3.28×10−9 cm3 s−1 at 700 K.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8607-8616 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the temperature, T, range of 300–600 K and the mean electron energy range 〈ε〉 of 0.19–1.0 eV, the total electron attachment rate constant for SF6 and c-C4F6 measured in dilute mixtures with N2, is virtually independent of T. Under the same experimental conditions the stabilized SF−6 anion does not undergo autodetachment but the stabilized c-C4F−6 anion undergoes a profound increase in autodetachment (by about four orders of magnitude). This difference between the SF−6 and the c-C4F−6 anions is attributed to the larger electron affinity of the SF6 molecule compared to the c-C4F6 molecule. The heat-activated autodetachment for c-C4F−6 is related to increases in the internal energy content of the c-C4F−6 anion and is found to have an activation energy of 0.237 eV. The "limiting electric field strength'' of SF6 was found to increase by ∼11% as T was increased from 300 to 600 K.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4238-4238 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7279-7279 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 24-35 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved pulsed Townsend technique for the measurement of electron transport parameters in gases is described. The accuracy and sensitivity of the technique have been investigated by performing, respectively, electron attachment coefficient measurements in pure O2 over a wide range of E/N at selected O2 pressures and by determining the electron attachment and ionization coefficients and electron drift velocity in CH4 over a wide E/N range. Good agreement has been obtained between the present and the previously published electron attachment coefficients in O2 and for the drift velocity measurements in CH4. The data on the electron attachment coefficient in CH4 (measured for the first time) showed that with the present improved pulsed Townsend method, electron attachment coefficients up to 10 times smaller than the ionization coefficients at a given E/N value can be accurately measured. Our measurements of the electron attachment and ionization coefficients in CH4 are in good agreement with a Boltzmann equation analysis of the electron gain and loss processes in CH4 using published electron scattering cross sections for this molecule.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3001-3015 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gas mixtures for possible use in diffuse discharge switching applications require both high dielectric strength and specific electron transport properties in the conducting and the opening stages of the operation of the switch. In the conducting stage, the electron drift velocity must be large, and the electron loss processes (e.g., due to electron attachment and recombination) must be low so as to maximize the current in the discharge while maintaining low-discharge impedance. In the opening stage, strong electron attachment along with high dielectric strength is required of the gas mixtures in order to extinguish the discharge as quickly as possible (and, thus, achieve a fast opening time) and to prevent arcing occurring between the switch electrodes due to the high voltages induced across the switch in the opening phase. Measurements of the electron drift velocity, attachment, ionization and transverse diffusion coefficients, and high-voltage dielectric strengths of several gas mixtures proposed as candidates for use in diffuse discharge switching applications have been made and are reported and discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1858-1865 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The drift velocity of electrons (w) in SiF4 and BF3 has been measured over the density-reduced electric field (E/N) range 0.5×10−17 V cm2 ≤E/N≤300×10−17 V cm2 using a pulsed Townsend experimental technique. The electron attachment (η/N) and ionization (α/N) coefficients have also been measured in SiF4 and BF3 over the E/N range 30×10−17 V cm2 ≤E/N≤300×10−17 V cm2 in the same experiment. The electron drift velocities in these two gases exhibit regions of negative differential conductivity (NDC) similar to but smaller in magnitude than those in CH4 and CF4 . The effective ionization coefficient (α¯/N) has been obtained from the η/N and α/N measurements in both gases, from which the high-voltage limiting electric field strengths (E/N)lim have been found to be 123×10−17 V cm2 for BF3 and 121×10−17 V cm2 for SiF4. The significance of these results in modeling gas discharges for a number of technological applications is indicated.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 52-59 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In general, the electron attachment rate constant ka (〈ε〉, T), as a function of the mean electron energy 〈ε〉 and temperature T for electronegative gases which attach electrons nondissociative ily, decreases greatly with T from room temperature to T(approximately-less-than)600 K, while the ka (〈ε〉, T) of electronegative gases which attach electrons dissociatively increases with increasing T. Based on recent studies at our laboratory on ka (〈ε〉, T), we investigated the variation with T (∼295–575 K) of the uniform field breakdown strength, (E/N)lim, for three classes of electronegative gases: (a) gases such as c-C4F8 (and c-C4F6, 1−C3F6) which attach strongly low-energy ((approximately-less-than)1 eV) electrons nondissociatively and for which ka (〈ε〉, T) decreases precipitously with T above ambient: (b) gases such as C2F6 and CF3Cl which attach electrons exclusively dissociatively and whose ka (〈ε〉, T) increases with T; and (c) gases such as C3F8 and n-C4F10 which attach electrons both nondissociatively and dissociatively over a common low-energy range and whose ka (〈ε〉, T) first decreases and then increases with T above ambient. The (E/N)lim(T) has been found to decrease significantly with T for (a), to decrease slowly with T for (c), and to increase slightly with T for (b). These changes in (E/N)lim follow those in ka (〈ε〉, T). A similar behavior is expected for other electronegative gaseous dielectrics in the respective three groups.
    Type of Medium: Electronic Resource
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