Electron Transport Coefficients in Hydrogen and Deuterium

Abstract

SummaryMeasurements have boon made of the drift velooity W and the ratio of diffusion ooefficient to mobility D/,.. for low energy electrons in deuterium at 77°K, and of D /,.. in hydrogen at 77 and 293°K. Tabulated data are given for D /,.. within the range 2x 10-20 .;; E/N .;; 1·2x 10-16 V cm2 and for W within the range 8x 10-20 .;; E/N .;; 9·5x 10-17 V cm2• The low temperature results show a considerably reduced scatter when oompared with previously published data and are of an aocuracy comparable with the results of recent measurements made at room temperature. The data obtained complement those of Lowke and of McIntosh thus completing a set from which a more acourate determination of low energy elastic and inelastic cross sections can be made.

Momentum Transfer Cross Section for e??Kr Scattering

“…The maximum value of E / N considered in this study was 2·0 Td (1 Td == [10][11][12][13][14][15][16][17][18][19][20][21] Vm 2 ), in order to limit the energy range of the present investigation to 0::; E ::; 4 eV. The upper limit is set by the availability of cross sections for hydrogen, which are assumed to be known sufficiently accurately over this energy range (Crompton and Morrison 1993;present issue p. 203).…”

“…The original transport data used to obtain the best estimate cross section am were increased by the quoted systematic errors (Elford et al 1992;England and Elford 1988) and a new cross section found by the procedure described in Section 2. The original transport coefficient data were then decreased by the quoted systematic errors and another cross section derived.…”

“…The large number of derivations of the momentum transfer cross section for krypton, am, from analyses of electron swarm transport data that exist in the literature, are in poor agreement (see for example Elford et al 1992), reflecting uncertainties in the experimental data and the intrinsic non-uniqueness of cross sections derived from transport data. Despite accurate experimental data, recent derivations, such as that of Hunter et al 1988 (based on an analysis of electron drift velocity data for pure krypton), suffer from significant uncertainty, arising from the relatively low sensitivity of the drift velocity to the momentum transfer cross section at energies in the vicinity of the Ramsauer-Townsend minimum.…”

“…1992) (where DT is the transverse diffusion coefficient and J. L the electron mobility) for electrons in a 0·4673% hydrogen-99·5327% krypton mixture; and the drift velocity, W, for electrons in two hydrogen-krypton mixtures containing 0·4673% and 1·686% hydrogen respectively . The use of hydrogen-krypton mixtures, rather than pure krypton, has a number of advantages (discussed in Elford et al 1992), in spite of the introduction of uncertainties in the assumed set of scattering cross sections for hydrogen, which necessarily increase the uncertainty in the derived krypton O"m.…”

“…This manifests itself as poor uniqueness in the derived cross section. The problem of uniqueness in the derived cross section, discussed by Elford et al (1992) and references therein, can be alleviated to some extent by using drift velocity data for krypton-hydrogen mixtures as the basis for deriving a cross section . The uncertainty in the derived cross section, due to the uniqueness problem, may be further reduced by basing the cross section on an analysis of two or more transport coefficients in such mixtures.…”