Onsager symmetry of the average ion near equilibrium

Abstract

The linear response of the average-ion model near local thermodynamical equilibrium (LTE) is written in Onsager's symmetric form. The symmetry shows up through a “spectral signature” of one-electron levels, which describes both the sensitivity of the level population to non-LTE radiation, and the effect of a non-LTE population on the spectral response of the plasma. In particular, we prove analytically the symmetry and negativity properties of the “response matrix” defined by More and Kato. More generally, we expect to speed up non-LTE atomic physics computations by using these linear response equations.