Development of an equation of state to characterize an electron beam interacting with an aluminum target

Abstract

The Equations Of State (EOS) of materials under extreme conditions of temperature and pressure can be experimentally studied, thanks to intense electron beam-target experiments. The latter are powerful tools to probe materials in the warm dense matter regime. At CEA/CESTA, we use the CESAR pulsed generator (1 MV, 300 kA). During an experimental shot, a high-power 800 keV, 100 kA, 20 mm-diameter, 100 ns electron pulse produces shock waves in an aluminum target. The behavior of the latter is explored by analyzing the time-history of its rear face velocity, as measured by photon Doppler velocimetry. Using simulations, we can test the accuracy of an EOS over a wide range of densities and temperatures. In addition, an accurate EOS allows for reduction of the uncertainties of the beam parameters that have an impact on beam energy deposition. We have observed that the measurements are not correctly restituted by the simulation codes when they use the available EOS (BLF, SESAME). Thanks to both published data and ab initio calculations, which are valid in the considered thermodynamic regime, we have developed a new EOS describing precisely the thermodynamic (isochoric) regime from one-half to one-third the normal density. The corresponding hydrodynamic simulations appear to be in much better agreement with the measurements. In addition, this new EOS has allowed us to refine the knowledge of the input electron beam parameters that have an impact on beam energy deposition.