The influence of continuum lowering on the equilibrium composition of plasma: case study of laser-induced plasma on a WC-Cu target

Abstract

The composition of the plasma obtained by laser ablation of cermet WC-Cu is calculated under the assumption of local thermodynamic equilibrium. Special attention is paid to the effect of lowering the ionization potential, the influence of which in the Saha equations is reflected both through the exponential Boltzmann term and through the partition functions of atomic and ionic species present in the plasma. The effects of these two terms are separated and quantified. It has been shown that the correction to the partition functions due to the reduction of the ionization potential is of greater importance than the correction to the Boltzmann term at higher temperatures for atomic species. It is thus necessary for the precise determination of the plasma composition, especially at higher temperatures. The effect of lowering the ionization potential on different types of atoms as well as on different ionic states is analyzed. The change of the partition function due to the lowering of ionization energy also affects the concentration of single charged ions in an amount comparable to the correction of the Boltzmann term.