| The process that The perturbed interface of two fluids with different densities is accelerated impulsively by an incident shock wave,is called Richtmyer-Meshkov Instability(RMI).In astrophysics and practical engineering problems,like supernova explosion and inertial confinement fusion(ICF),RMI is generally generating in plasmas with hig-energy density.which results in multiple physical coupling in one system.Different from RMI in neutral medium,the self-generated magnetic field will be induced when RMI start arising in plasmas,which may lead to the different flow phenomena.Especially in ICF,the self-generated magnetic field can suppress the electron thermal conductivity which would be contributed to ignition.Although there have been many studies on the superssion of RMI by external magnetic field,moreover,there have been a few theoretical studies on the self-generated magnetic field in Rayleigh Taylor instability(RTI).However,the study on the self-generated magnetic field of RMI in plasma is still quite weak,they are still unclear that the physical mechanism of self-generated magnetic field in RMI and its effect on flow of electrons and ions.This paper focus on the problem of self-generated magnetic field of RMI in plasmas,the numerical simulation method based on two-fluid Magnetohydrodynamics(two-fluid MHD)was developed,one parallel code based on two fluid MHD was developed.Futhermore,the generating mechanism of self-generated magnetic field of RMI in plasma and its influence on the evolution of flow field were studied.The main results are as follows:Firstly.In this paper,a high accuracy numerical method and two-dimensional parallel code are developed based on ion and electron two-fluid MHD model.The ideal single-fluid MHD model is usually used in plasma numerical simulation,however,the single-fluid model cannot reflect the self-generated magnetic field effect.For this reason,the numerical method and code based on two-fluid model are developed.For problem like RMI,which contains the interaction of interface and shock with strong discontinuities.This paper presented a hybrid high accuracy method-hybrid monotonicity-preserving Scheme(referred to as HMP5)which combines the advantages of traditional monotonicity-preserving scheme and piecewise parabola method.The HMP5 improves the robustness without the decreasing of accuracy.In addition,in order to investigate the adaptability of two-fluid MHD model,the effective scale ranges of Euler equations and NS equations are given quantitatively by solving boltzmann equation in this paper,the results show that the wo-fluid MHD model can be used to study the self-generated magnetic field at the urrent scale.Secondlyiin this paper,the mechanism of generation of self-generated magnetic field in RMI is explained as well as a theoretically predicted model of the peak intensity in seld-generated magnetic field is derived by combining theoretical analysis and numerical simulation.According to the analysis of two-fluid MHD model,the key of self-generated magnetic field is the velocity separation of electrons and ions.Based on this,the electron and ion velocities after shock wave are analyzed through shock wave relation,the results show that the velocity separation of electron and ion after shock wave is proportional to the square root of particle mass ratio.Subsequently,through numerical simulation,it was found that the velocity difference of electrons and ions still played a key role in the evolution of the self-generated magnetic field at different stages of the subsequent development of RMI,the distribution of velocity diff-erence of electrons and ions determines the distribution of self-generated electric field,and the self-generating magnetic field is the time integral of self-generated electric field.In order to explore the largest magnitude of self-generated magnetic field at different stages of RMI evolution,a prediction model for the peak value of self-generated magnetic field intensity of single-mode RMI is established in this paper by combining Faracday's law with the momentum equation of flow field,tt is found that the predicted value of the model is in good agreement with the numerical simulation result,which shows the validity of the model.Finally,the effect of self-generated magnetic field on electron and ion flow is investigated and its mechanism is analyzed.Through the numerical simulation based on two-fluid MHD model,RMI of single mode,multi-mode,and multi-mode reshock was compared and studied with or without selt-generated electromagnetic field.The results show that compared with the situation without self-generated electromagnetic field,when there is self-generated electromagnetic field,the mixing zone width of electron in RMI increased siginificantly faster,and after a period of time of RMI developing,some new high wavenumber perturbation modes would be generated at the spike of the electronic interface,which results in the small-scale structures faster arised in flow field.while it doesn't make much difference for ions.Combined with the analysis of electromagnetic field properties,it can be concluded that:The accelerated growth of electron mixing zone width is due to the coupling effect of self-generated electric field on electrons and ions,which makes the motion of low-mass electrons tend to follow the motion of ions.It is equivalent to a variable acceleration RTI for electrons under electric field force of ions.Well,the high-wavenumber perturbation generated in the electronic interface is caused by the electrons which are moving forward flow direction near the spike skewing to the both sides of the spike under the lorentz force of the self-generated magnetic field,The perturbation crest appear where some of the electrons are concentratedIn this paper,the problem of self-generated magnetic field of RMI in plasma is studied systematically.The mechanism of RMI induced self-generated magnetic field and the effect of self-generated magnetic field on the development of interface instability are presented,it provides a reliable numerical method and data for the study of RMI under two-fluid MHD model,it promotes the development of the research on interface instability under the condition of multiple physical coupling and has important scientific significance and application background. |
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