Theoretical And Numerical Simulation Studies On The Mechanical Effects Of Material Ionization Under Extreme Shock Impacting

Inertial confinement fusion(ICF)restricts the particles themselves through the inertial action of the particles,thus forming a strong convergent shock wave so that the plasma with extremely high density at the central convergent pole can be maintained for a certain time under ultrahigh temperature and ultrahigh pressure conditions and then realize fusion ignition.The process of implosion convergence is affected by extreme conditions,and the material will change from the original solid/liquid/gas state to the plasma state.Its physical properties and thermodynamic conditions have undergone drastic changes,such as material density,temperature,viscosity,etc.,which brings great challenges to fusion research.There is a strong ionization effect in front of the shock wave compression wave.The diffusion difference between ions and electrons after the wave will cause a large number of free electrons to converge near the ignition pole in advance,which may cause special physical and mechanical effects.Literature reviews indicate that there are few reports about the impact of the ionization effect on the hydrodynamic interface instability and its effects on the convergence process.This paper first transplanted the molecular dynamics program of the open source code LAMMPS(Large-scale Atomic/Molecular Massively Parallel Simulator)electronic force field potential function(eFF)to the Sunway supercomputing platform,performed large-scale numerical simulation of the impact compression ionization effect on different configurations(plane,cylindrical)of the Li/H2 interface under extreme impact loading conditions,and studied the charge separation phenomenon and mechanical effects in the impact process.The relevant theoretical models of the electric field/force field changes at the interface and the convergence pole are established,and the relevant physical and mechanical effects and mechanisms are revealed.The main contents of this paper are as follows:1.The molecular dynamics LAMMPS code with cylindrical and spherical loading boundary conditions was developed and transplanted to the domestic Sunway "masterslave" heterogeneous supercomputing platform.The simulation scale of the electronic force field potential function on the scale of 10 million particles is realized with parallel computation optimization to the scale of 100000 cores.2.The dynamic process of the shock wave impacting the plane Li/H2 interface was simulated.After the shock wave compresses the ionization of the material,the electron/ion creates an additional electric field through bipolar diffusion and forms a quasistable electron/ion separation zone near the shock front.Based on the simulation results,a one-dimensional microscopic theoretical model is established,and then a macroscopic mechanical model is established through multiscale analysis.It is applied to the nonlinear model of Richtmyer-Meshkov(RM)instability amplitude growth in fluid mechanics and validated with macroscopic Nova experimental data.The hydrodynamic effect of the shock-induced additional electric field is theoretically verified.3.The dynamic process of converging a strong shock wave impacting the cylindrical Li/H2 interface was simulated.It is found that there is not only a strong charge separation phenomenon in the converging process but also that the electrons converge to the pole of the ignition point in advance,forming a special polar constraint electric field.Statistical analysis shows that the additional force field induced by charge separation not only increases the velocity of the convergent shock wave but also presents a new phenomenon of the "platform effect" in the plasma density of the convergent pole region,which is constrained by the polar electric field.4.A theoretical model of the change in the electric field/force field at the convergence pole was established,and the mechanical constraint mechanism of the pole-constrained electric field on the plasma material in the polar region during the convergence process was analyzed theoretically.The new mechanism of the density change of the pole-constrained plasma is explained,and the positive significance of the mechanical effect of the ionization on the ICF fusion ignition is revealed.