Transport properties in a two-temperature plasma: Theory and application -art. no. 026409

An alternate derivation of transport properties in a two-temperature plasma has been performed. Indeed, recent works have shown that the simplified th eory of transport properties out of thermal equilibrium introduced by Devot o and then Bonnefoi, very often used in two-temperature modeling, is questi onable and particularly does not work when calculating the combined diffusi on coefficients of Murphy. Thus, in this paper, transport properties are de rived without Bonnefoi's assumptions in a nonreactive two-temperature plasm a, assuming chemical equilibrium is achieved. The electron kinetic temperat ure T-e is supposed to be different from that of heavy species T-h. Only el astic processes are considered in a collision-dominated plasma. The resolut ion of Boltzmann's equation, thanks to the Chapman-Enskog method, is used t o calculate transport coefficients from sets of linear equations. The solut ion of these systems allows transport coefficients to be written as linear combinations of collision integrals, which take into account the interactio n potential for a collision between two particles. These linear combination s are derived by extending the definition and the calculation of bracket in tegrals introduced by Chapman et al. to the thermal nonequilibrium case. Th e obtained results are rigorously the same as those of Hirschfelder et al. at thermal equilibrium. The derivation of diffusion velocity and heat flux shows the contribution of a new gradient, that of the temperature ratio the ta = T-e/T-h. An application is presented for a two-temperature argon plasm a. First, it is shown that the two-temperature linear combinations of colli sion integrals are drastically modified with respect to equilibrium. Second ly, the two-temperature simplified theory of transport coefficients of Devo to and Bonnefoi underestimates the electron thermal conductivity with respe ct to the accurate value at T-e = 20 000 K. Lastly, contrary to the simplif ied theory of transport coefficients, the diffusion coefficients satisfy th e symmetry conditions. An example is given at T-e = 6000 K for different va lues of theta for the diffusion coefficient between electrons and heavy spe cies De-Ar as well as for that between argon atoms and argon ions DAr-Ar+.