Influence of the equation of state on the compression and heating of hydrogen

This paper presents two-dimensional hydrodynamic simulations of implosion of a multilayered cylindrical target that is driven by an intense heavy ion beam which has an annular focal spot. The target consists of a hollow lead cylinder which is filled with hydrogen at one tenth of the solid density at room temperature. The beam is assumed to be made of 2.7-GeV/u uranium ions and six different cases for the beam intensity (total number of particles in the beam, N) are considered. In each of these six cases the particles are delivered in single bunches, 20 ns long. The simulations have been carried out using a two-dimensional hydrodynamic computer code BIG-2. A multiple shock reflection scheme is employed in these calculations that leads to very high densities of the compressed hydrogen while the temperature remains relatively low. In this study we have used two different equation-of-state models for hydrogen, namely, the SESAME data and a model that includes molecular dissociation that is based on a fluid variational theory in the neutral fluid region which is replaced by Padé approximation in the fully ionized plasma region. Our calculations show that the latter model predicts higher densities, higher pressures but lower temperatures compared to the SESAME model. The differences in the results are more pronounced for lower driving energies (lower beam intensities).