Equation of state of weakly nonideal plasmas and electroneutrality condition

Abstract

Derivation of weakly nonideal hydrogen plasma EOS and detailed results on partial contributions to plasma pressure for the Sun's interior are presented. The impetus for this work was the demand for high accuracy of the EOS of the solar plasma in relation to the problems of modern helioseismology, accuracy sufficient for reproducing the velocity of sound on the Sun from optical measurements with errors not exceeding 10−4. In our computations the relativistic corrections, degeneracy of electrons, radiation pressure in plasma, the Coulomb interaction in the Debye–Hückel approximation together with diffraction and exchange corrections and the contribution of bound and scattering states are taken into account. The analysis of the electrical neutrality condition in terms of activities and concentrations is presented. It is shown how to modify the relation between activities and concentrations for removing divergences of the Hartree contribution, representing the first order correction due to the Coulomb interaction in plasma. For the conditions of the Sun trajectory it is shown that the widely used practice of ignoring the neutrality condition in terms of activities, taking the Hartree contribution into account, gives a maximal error for plasma pressure of the order of 10−5.