Behavior of the coupling parameter under isochoric heating in a high-Z plasma

The ion-ion coupling parameter Gamma is estimated for tungsten along the rho = 40 g/cm(3) isochore corresponding to twice the normal density with temperatures ranging from 10 eV to 5 keV. Using a variety of approaches from a spherical Thomas-Fermi ion to a full three-dimensional orbital-free method, we show that along an isochore the effective ionic coupling parameter is almost constant over a wide range of temperatures ( in our case Gamma similar or equal to 20) due to the competition between rising temperatures and increased ionization. This Gamma-plateau effect depends on the chosen density and is well delineated at normal density but almost disappears at five times the normal density. This effect could be used to obtain well-defined and predictable experimental conditions.