Example: calculation of electron transport coefficients in Xenon, Methane and their mixtures.

Electron transport coefficients are different in atomic gases (such as Xenon) and in molecular gases (such as Methane). Elastic collisions of electrons with atoms occurs in the first case. Electrons colliions with molecules occurs as both elastic and inelastic processes. A small amount of molecular addition changes strongly the electron transport coefficients in mixtures. Two figures present calculations of electron drift velocity and transverse diffusion coefficient as a function of the parameter E/N, which is the ratio of the electric field strength and the gas density. The calculated values are compared with experimental data. Third figure shows the mean electron energy calculated for pure Xenon and Methane and their mixture. The electron tramsport coefficients depends on the ratio E/N in gases. The mean energy of electrons exceeds the gas temperature for high E/N. The electrons become “hot”. The drift velocity of hot electrons is less than the drift velocity of “thermal” electrons in molecular Methane for the same values of the parameter E/N. The mean energy of electrons is less than that in pure Xe but higher than in pure Methane for the mixture Xe+1%CH4. It leads to increasing of the drift velocity in the mixture compare with the pure Xe.

Результаты расчетов и эксперимента для скорости дрифта в ксеноне, метане и их смеси. Поперечный коэффициент диффузии.
Сравнение результатов расчетов с экспериментальными данными для скорости дрифта в ксеноне, метане и их смеси. Эксперимент: Xe+10%CH4 [1], чистый CH4 – [2], [3], [4], [5].
Сравнение результатов расчетов с экспериментальными данными для поперечного коэффициента диффузии в ксеноне, метане и их смеси. Эксперимент: pure CH4 – [6].

Mean electron energy in pure xenon, methane and Xe + 1%CH4 mixture.
Mean electron energy in pure xenon, methane and Xe + 1%CH4 mixture.
References

[1] Christophorou L.G., Maxey D.V., McCorkle D.L., Carter J.G. “Xe-containing fast gas mixtures for gas-filled detectors.” Nuclear Instr. and Methods, 1980, v.171, p.491.

[2] Nakamura Y. Technical Report ED-84-28 IEEE Japan, 1984, р.3311.

[3] Pollock W.J. Trans. Faraday Soc., 1968, V.68, р.2919.

[4] Wagner E.B., Davies F.J., Hurst G.S. Journal Chem. Phys., 1967, V.47, р.3138.

[5] Hunter S.R., Carter J.G., Christophorou L.G. Journal Applied Phys., 1986, V.60, р.24.

[6] Duncan C.W., Walker I.C. Collision cross-section for low energy electrons in methane. Journal Chem. Soc. Faraday Trans. II, 1982, V.68, р.1514.

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