Research On The Radiation Temperature And Radiation Uniformity In Z-pinch Dynamic Hohlraum And The Fluid Instability In Ablator

Controllable inertial confinement fusion is an important way to solve the human energy crisis and environment crisis.Z-pinch dynamic hohlraum is one of the competitive ways to drive inertial confinement fusion due to the excellent properties,such as high radiation conversion efficiency,low cost of X-ray energy and larger fusion energy gain.The study and discussion on the issues existing in the process of dynamic hohlraum driving inertial confinement fusion is significant and valuable.There are still many problems need to be investigated in the process of Z-pinch dynamic hohlraum driving inertial confinement fusion.In order to increase the radiation conversion efficiency and improve the radiation uniformity in the dynamic hohlraum and suppress the fluid instability at the process of capsule implosion,the related factors affecting radiation temperature in dynamic hohlraum are analyzed,and the reasons of radiation non-uniformity around the surface of fusion capsule are discussed,and the fluid instabilities at the inner and outter surface of ablator are explored through combining theoretic analysis and radiation hydrodynamics simulations.Firstly,the physical models of radiation hydrodynamics,the equation of state and the radiation opacity are introduced,and the radiation hydrodynamics code used in this paper is benchmarked by several published works.The process of producing radiation and propagating radiaton is simulated.It is found that the radiation is produced from the high-temperature electrons of foam which is compressed by the shock,and the radiation spectrum approximates the Planck spectrum.Most of the radiation in the foam propagates with radiation heating wave.Some percent of high-energy x-rays can penetrate directly through the foam with the light speed.Based on the impact dynamics process,the energy conversion processes in dynamic hohlraum are analyzed.Two kinds of theoretical models are developed to study the main factors influencing the radiation temperature in hohlraum,and some radiation hydrodynamics simulations are also performed to verify the theoretical models.The results show that the temperature in hohlraum can be increased when the foam is made up by materials with low heat capacity.Redution of the foam density can increase the radiation temperature,but it also reduces the obtained internal energy of foam,thus also reduces the total radiation energy released by the foam.In addition,when the plasma shell has a larger density than the foam,decresing the density of plasma shell can increase the radiation temperature in the dynamics hohlarum.Under the same current pulse,the mass of the wire array should be setup slightly higher than the optimal mass,so that the radiation temperature in hohlraum can get higher.Secondly,the main reasons that cause the radiation non-uniformity around the capsule are discussed.The main factors influcing the speed of radiation heating wave are analyzed through the theoretical model and simulations of radiation hydrodynamics.The radiation non-uniformity around the capsule induced by the plasma shell with different shapes is explored through radiation hydrodynamics simulations.The results indicate that the time difference between the cylindrical radiation heating wave reaching the equator and the polar of capsule is a possible reason of radiation non-uniformity.In addition,the obliquely impact of the plasma shell on the foam can increase the radition non-uniformity and even lead to the asymmetry implosion of capusle.The perturbation in plasma shell will not induce the radiation non-uniformity around the capsule,but it can result in the radiation loss.Larger amplitude or smaller wavelength can lead to more drastic radiation loss.The high-enrgy X-ray which can directly penetrate the foam to ablate the capsule are also dicussed,which may be the main reason of the capulse implosion like a rugby under the condition of driving ICF.Thirdly,the development process of fluid instability at the inner and outter surface of the ablator is studied by theoretical analysis and simulations.The results show that the increasing of ablation velocity and plasma blow-off velocity,or decreasing of the sound speed after shock can reduce the ablative Richtmyer-Meshkov(RM)instability at the ablation front.The high-Z dopant in plastic ablator can suppress the growth of RM instability.Increasing the ablation velocity and the density gradient scale length at ablation front can reduce the linear growth of the ablative RT instability.The doped plastic target has a smaller linear growth rate of RT instability,which is attributed to the smaller acceleration.When a new linear growth rate eliminating the influence of acceleration is employed to evaluate the growth of RT instability,it is found that perturbation growth in the pure plastic target is less than that in the doped target due to the larger ablaton velocity and larger density gradient scale length.The growth of classical RM instability at the inner interface of ablator is depended on the density of ablator and the abaltion pressure.It is found that the perturbation in the interface of Be ablator has a lower growth than that in the interface of CH plastic abltor at the same radiation pulse drive.In addition,it is found that the profile of radiation pulse has a significant effect on the development of interface perturbation,which can change the growth direction of perturbation.The growth of interface perturbation can be suppressed by modulating the shape of the radiation pulse.