Study On Instability Of Single-mode Interface Under Extreme Conditions With Molecular Dynamics Simulation

When an incident shock strikes a corrugated contact discontinuity between two kinds of materials with different densities and compressibility,the initial corrugated interface amplitude will evolve and eventually develop into turbulent mixing.This kind of phenomenon is so-called Richtmyer-Meshkov instability(RMI).RMI is one of key fundamental problems in Inertial Confinement Fusion(ICF)regime,in which the most challenging question comes from extreme thermodynamic conditions(P?100 GPoa,T?10000 K).In such conditions,solid or gas material will directly be ionized to plasma after shock,the hydrodynamic conditions,thermodynamic states,as well as material physical properties such as diffusivity,conductivity,viscosity etc.will undergo dramatic change,presenting great challenges to the related theoretical,experi-ments and numerical simulation.Up to now,works on RMI at extreme thermodynamic conditions are rarely reported.Based on such situations,the RMI cases of Cu-He/Ar under different loading conditions and scales(micro to nano scales)are firstly simulated with classical predefined-potential-based molecular dynamics,in which no ionization effects is considered.The results confirm the consistency of the micro and macro scale RMI laws Then with the consideration of ionization effects,the RMI cases of Li-H2 under similar extreme shock conditions and nano scales are simulated with eFF molecu-lar dynamics.The results indicate some new characteristics in RMI evolutions.Finally the mechanism of this new characteristics of RMI evolution is analyzed and verified.The main conclusions are follows:1.The proper computational parameters of molecular dynamics simulation on mi-cro/nano scale RMI case are determined with considerable generality by comparative optimization of time step,computational zone scales as well loading styles,etc.2.It is proved that the micro/nano scale RMI shares the same evolution process and laws with macro scale RMI in computational time scale.3.It is found that some new characteristics are presented in RMI amplitude evolu-tion under extreme conditions,i.e.,the prolonged linear region and elevated nonlinear region in dimensionless amplitude increasing history curves as compared with non-ionization cases.The conclusion is partly confirmed by Nova experiments.4.It is found that the electron/ion separation is produced by strong shock in ex-treme loading conditions,inducing an extra electric field along RMI evolution field.The extra electric field intensity is nonuniform along shock moving direction,which is obviously affected by shock compressing strength and its position as well as material ionization properties5.It is found that the effects of extra electric field on RMI is not monotonous positive or negative.The eventual results of RMI evolution is controlled obviously by the relative acceleration difference at positions of spike and bubble under the work of extra electric field.This is the mechanism to explain the new characteristics of RMI amplitude evolution under extreme conditions.In fact,it is the coupling effects of RMI and RTI(Rayleigh-Taylor instability)in terms of hydrodynamics.