FAST-ION STOPPING POWER IN HOT, DENSE, STRONGLY-COUPLED PLASMA

Abstract

The relativistic form of the Bethe fast-ion stopping power involving the transverse dielectric function, as given by Landau and Lifshitz, is applied to calculation of atomic ion stopping in hot, dense plasmas in which the ions are strongly coupled ( r o c p > > 1). An average-atom plasma model, suitable for implementation on a PC spreadsheet, is described. This model, which provides the basis of a calculation of a bound-free and free-free representation of the plasma excitation function, incorporates several novel enhancements over the standard one-component plasma (OCP) or Debye-Huckel models. In highly ionised (Z* > > 1) plasmas, a frequently found situation is that the ions appear strongly coupled while the continuum electrons remain weakly coupled. Thus, while the Debye-Huckel treatment may therefore remain valid for the electrons, the OCP approximation for the ion component may not hold except at very much higher densities. The model therefore allows for electron polarisation within an ion sphere and treats the influence of electron screening on the ion dynamics. These effects are incorporated into a continuum lowering model which includes microfield (Stark) fluctuations. The plasma model also provides a reasonable treatment of the plasma collective effects around the plasma resonance. Since spectroscopic accuracy is not demanded for stopping power calculations provided that the appropriate sum rule is obeyed, use is made of an approximate analytical formula for the atomic energy levels. Bound-bound transitions are omitted the bound-bound oscillator strength being appropriately transferred to the bound-free. Calculations of excitation functions and stopping powers are presented for lOOeV aluminium and 300eV lead plasmas at normal densities. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988713