Study On The Equation Of State Of Low-density Foam Au

In inertial confinement fusion,high Z materials,such as gold,are usually used as wall materials in hohlraum.The laser energy is absorbed by the wall materials through inverse bremsstrahlung absorption and converted to X-ray flux.As a result,the homogeneous radiation field is formed due to the X-ray flux.The energy conversion efficiency from the laser to the X-ray takes the significant value to improve the energy use efficiency and achieve the ignition in indirect-driven ICF.gold foam,one kind of porous materials,is an alternative wall material in hohlraum,which could decrease the energy loss and increase the laser energy conversion efficiency.The equation of state for gold foam is indispensable for the simulation of gold foam-wall hohlraum.Currently,the EOS for gold foam used in the simulation comes from the EOS database,such as SESAME library or QEOS model.The EOS experiments for gold foam have not been reported so far.Therefore,the gold foam is chosen to study its equation of state in different pressure range from three different aspects,as well as to verify the theoretical models.Firstly,based on Geng HY model,which possesses the widely pressure range appli-cation,the influence of input parameters,the porosity m,the parameter R,the anharmonic parameters l and the intial temperature,to the prediction Hugoniot curve have been dis-cussed.The compressed porous Cu,which have been experimental researched before,have been computed by the numerical program based on the Geng HY model.The pre-diction curves whose parameter R was computed by the combination of the cold pressure curve and the Hugoniot curve of solid regime was proved to be more consistent with the experiment data than other method of computing R during the computed pressure range of 10GPa?300GPa.However,the different values of l seem to have no influence on the predicted curves at the same calculation pressure range.What's more,for different initial temperatures,the discrepancy exist only in low pressure range(?10GPa);while the diver-sity area extended to the high pressure with the initial temperature increase obviously.In other words,the effect of preheating could be ignored in high pressure range when the preheating temperature is not beyond 5000K.Secondly,the molecular dynamics method have been employed to simulate the shock response of gold foam.Before the shock compression simulation,the embeded-atom-method potentials have been chosen by the simulation compression state of solid gold.The simulation results suggest that the two potentials proposed by the Zhakhovskii and Olsson,respectively,are fit for describing the interaction of gold atoms during the shock loading process.Besides,the effect of the outer-diameter and the thickness of the sphere shell to the stability of the simulated configuration have also been simulated.The influ-ence of the outer-diameter to the stability is weak which can be ignored.However,it dominates the porosity of the configuration.The configurations are unstable when the thickness of the shell is less than 1.3nm in these simulation.The stability configura-tions were used to simulate the shock response in the 1GPa?1TPa pressure range.The comparison between the simulation results and the prediction Hugoniot curves from the SESAME 2700,QEOS model and the Geng HY model indicates that the diversity are existing among each other.However,the trend between the simulation results with the prediction curves from SESAME 2700 and the Geng HY model are in consistent.More-over,the predictions for solid gold from the SESAME 2700 and the QEOS model are almost the same,while the diversity for predictions for porous gold are obvious which in-crease with the increase of the porosity.This phenomenon provides an alternative method to carry out shock experiments for high porous materials to confirm the correctness of the two models.In the third part,the shock experiments for gold foam with an initial density ?00 ?3.2g/cm3 have been carried out.utilizing the impedance match technique and passive shock breakout diagnostic system,the experiments for gold foam in the pressure near 2TPa were performed on SG-III prototype facility.The shock state of shocked gold foam have been obtained by using the impedance method.Furthermore,the experiment data due to unsteady shock wave were corrected by the unsteady loading source experiments.The experiment results compared with the prediction curves from SESAME 2700,QEOS model and Geng HY model suggest that SESAME 2700 and QEOS could approximately describe the shock state of gold foam in the TPa pressure range.However,the Geng HY model sesames to take a poor prediction than SESAME 2700 and QEOS model,which is possibly caused by the over consideration of the effect of heating.The theoretical research on the porous materials could help us have a better under-standing of the universal thermodynamic properties of porous materials.The molecular dynamic simulation for gold foam makes the analysis of the evolution of thermodynamic quantities in gold foam,as well as a supplement to theoretical research and experimen-tal research.The corresponding EOS experimental research for gold foam make a better understanding of the thermodynamic characteristics for gold foam.simultaneously,these experiments add the EOS data for gold where the principal Hugoniot could not be attained by using solid gold.What's more,the experiment data could provide a reliable basis for the identification of different theoretical models.