Heat flux effects in Ohm's law

Abstract

The velocity dependence of the collision frequency nu in a plasma causes the appearance of the thermoelectric field and heat flux effects in Ohm's law. An artificial dependence on electron velocity nu of v varies as nu -2 allows an exact representation of the two terms valid for any isotropic lowest order distribution function. The thermoelectric coefficient and the electric conductivity are isotropic (i.e. independent of the Hall parameter) in this model, and there is a magnetomotive force, additional to the usual v*B/c term, equal to 2(qT*B)/5(pec) where qT is the total electron flux (measured in the ion rest frame) and pe is the electron pressure. Similarly the inertial contribution to Ohm's law depends on delta qT/ delta t. Comparison is made with the full Braginskii transport (as modified by Epperlein and Haines 1986), including electron-electron collisions, for a lowest order Maxwellian distribution. If Ohm's law is written in a more physical form to include a term in qe*B (where qe is the electron heat flux measured in the electron fluid rest frame), it leads to a good approximation also to an isotropic thermoelectric coefficient and electric conductivity. Some applications of this new form of Ohm's law are outlined, particularly the role of the qe*B term.