Higher-order contributions to transport coefficients in two-temperature hydrogen thermal plasma

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Abstract
Within the framework of Chapman-Enskog method, electron transport properties and their higher-order contributions have been studied in temperature range 5000–40 000 K at different pressures for hydrogen thermal plasma in local thermodynamic equilibrium (LTE) and non-local thermodynamic equilibrium (NLTE) regimes. Two cases of thermal plasma have been considered: (i) Ground state (GS) plasma in which all atomic hydrogen has been assumed to be in ground state and (ii) the excited state (ES) plasma in which hydrogen atoms are distributed in various possible electronically excited states (EES). The plasma composition is calculated by modified Saha equation of van de Sanden et al. The influence of non-equilibrium parameter θ (=Te/Th) on these properties has been examined in both the cases. It has been observed that both EES and θ modify the plasma composition and consequently affect the electron transport properties (viz., electron thermal conductivity, electrical conductivity, thermal diffusion and thermal diffusion ratio). It is shown that non-equilibrium parameter θ has meager effect on the higher-order convergence in comparison to EES. The unique behaviour observed for third-order contribution to these transport properties in GS plasma for small values of θ could be explained only when EES are taken into account. It is noted that EES show their influence on higher-orders to a considerable extent even when e-H(n) cross-sections are replaced by the ground state ones. Thus electron transport coefficients and their higher-order contributions are affected significantly due to inclusion of EES in LTE and NLTE plasmas.

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