Ablative Rayleigh-Taylor Instability Under Nonlocal Heat Transport Regime

The vast majority of matter in the known universe is in a state of high energy density(energy density greater than 105J/cm3).High energy density fluids are ubiquitous in astrophysical processes and in many important defense and engineering applications,such as supernova explosions and inertial confinement fusion(ICF),which inevitably involve changes in fluid density and accelerated interfaces of fluids of different densities.The physical process of destabilizing growth of perturbations at the interface through the Rayleigh-Taylor instability(RTI)plays a critical role in these applications.Matter at high energy density conditions often exists in a plasma state,consisting of fully or partially ionized electrons and ions,and is often also accompanied by a dramatic stratification of density and temperature,which results in intense heat transport and mass ablation at the interface.This kind of RTI with ablation effect is called ablative RTI(ARTI).The classical theory of thermal transport based on the assumption of local equilibrium often fails in ICF relevant environments,with the nonlocal thermal transport effects non-neglectable.In the context of ARTI and electron nonlocal heat transport(NLHT)in ICF,this thesis systematically studies the phenomena,mechanisms and regularities of the influence of electron NLHT caused by steep temperature gradient and long mean free path hot electrons on the growth of ARTI by theoretical analysis and direct numerical simulation.The main works and research results are as follows:(1)A three-dimensional multigroup diffusion electron NLHT parallel program is developed and coupled with a plasma fluid dynamics program ART for calculation.The effects of electron NLHT due to steep temperature gradients in the ICF on the two-dimensional single-mode ARTI up to the highly nonlinear phase are investigated for the first time.It is found that as well as its role in the linear stabilization of ARTI growth by NLHT,NLHT can also mitigate ARTI bubble nonlinear growth after the first saturation to classical terminal velocity,compared with what is predicted by the local Spitzer-H?rm electron heat transport model.The key factor affecting the reduction in the linear growth rate is the enhancement of the ablation velocity by preheating caused by NLHT.It is found that NLHT mitigates nonlinear bubble growth through a mechanism involving reduction of vorticity generation.NLHT enhances ablation near the spike tip and slows down the spike,leading to weaker vortex generation as the pump of bubble reacceleration in the nonlinear stage.NLHT more effectively reduces the nonlinear growth of shorter-wavelength ARTI modes seeded by the laser imprinting phase in direct-drive laser fusion.(2)The effects of hot-electron energy transport on the evolution of two-dimensional single-mode ARTI are investigated by numerical simulations with a multigroup diffusion model.Hot electrons with complex distribution function are simplified to a mono-energetic group of electrons.It is found that the linear growth rate of ARTI can be significantly reduced,and the stabilizing effect on the growth of spikes is stronger than that of bubbles.The reduction of linear growth rate is mainly due to the increase of ablation velocity and density gradient scale length by hot electrons.The increase of ablation velocity enhances the ablative stabilization effect,and the increase of density gradient scale length reduces the effective Atwood number.The self-consistent stability theory gives a good approximation to the linear growth rate of ARTI in the presence of hot electrons.This linear stabilization effect is greater for small wavelengths and thus hot electrons may change the linear cutoff wavelength of ARTI.In the current simulation parameter range,hot electrons with higher energy have a more significant effect on the decrease of peak density and the increase of density gradient scale length.Increasing the amount of hot electrons,the linear growth rate of ARTI does not keep decreasing.After exceeding a certain hot electron number density,the growth rate of ARTI increases slowly as the increase in shell acceleration by hot electron begins to dominate.(3)The characteristics of multimode ARTI evolution and the effect of hot electron transport on the growth of multimode ARTI bubble front are investigated based on direct numerical simulations.It is found that the multimode ARTI bubble front shows a self-similar growth pattern in the highly nonlinear phase,and the self-similar growth coefficient is closely related to the initial perturbation and may have different values at different time.Hot electrons can affect the initial perturbation spectrum amplitude of multimode ARTI.Hot electrons can significantly delay the growth of multimode ARTI bubble front into the self-similar growth phase.