Using a relativistic electron beam to generate warm dense matter for equation of state studies

Summary form only given. Experimental equation-of-state (EOS) data are difficult to obtain for warm dense matter (WDM)-ionized materials at near-solid densities and temperatures ranging from a few to tens of electron volts-due to the difficulty in preparing suitable plasmas without significant density gradients and transient phenomena. We propose that the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility can be used to create a temporally stationary and spatially uniform WDM. DARHT has an 18 MeV electron beam with 2 kA of current and a programmable pulse length of 20 ns to 200 ns. This poster describes how Monte Carlo n-Particle (MCNP) radiation transport and LASNEX hydrodynamics codes were used to demonstrate that the DARHT beam is favorable for avoiding the problems that have hindered past attempts to constrain WDM properties. In our concept, a 60 ns pulse of electrons is focused onto a small, cylindrical (1 mm diameter x 1 mm long) foam target, which is inside a stiff high-heat capacity tube that both confines the WDM and allows pressure measurements. In our model, the foam is made of 30% density Au and the tamper is a B4C tube. An MCNP model of the DARHT beam investigated electron collisions and the amount of energy deposited in the foam target. The MCNP data became the basis for a LASNEX source model, where the total energy was distributed over a 60 ns time-dependent linear ramp consistent with the DARHT pulse. We used LASNEX to calculate the evolution of the foam EOS properties during and after deposition. Besides indicating that a ~3 to 4 eV Au plasma can be achieved, LASNEX models also showed that the WDM generates a shock wave into the tamper whose speed can be measured using photonic Doppler velocimetry. EOS pressures can be identified to better than 10% precision. These pressures can be correlated to energy deposition with electron spectrometry in order to obtain the Au EOS. Radial uniformity in the DARHT beam was also investigated. To further obtain uniform radial energy deposition, MCNP calculations were carried out with radial beam filters. Results are presented.