The calculation of free electron density in Cassandra

Abstract Cassandra is an AWE opacity code used to model plasmas in local thermal equilibrium: there is a desire to expand its use to calculating plasma equations of state. Cassandra' s self-consistent field calculation ( scf ) uses the local density approximation for bounds states and has a free electron contribution based upon the Thomas-Fermi model [B.J.B. Crowley et al., J. Quant. Spectro. Radiat. Trans. 71 , 257(2001)]. Whilst this is applicable for very high temperature or low density plasmas; in hot and dense matter the effect of ionization will lead to discontinuities in the effective ionisation, Z ⋆ . The electron contribution to hydrostatic pressure is associated with Z ⋆ , thus these discontinuities produce unphysical jumps in the resulting calculated material pressure. We describe a procedure to mitigate the effect by calculating the free electron wave functions within the generalized ion-cell model [B.J.B. Crowley et al., Phys. Rev. A 41 , 2179(1990)], and thus explicitly calculate free-electron resonances.