Thermodynamic And Optical Properties Of Warm Dense Argon And Helium Under Multiple Reverberation Shock Compression

Astrosphere structure evolution and confinement fusion process both involve the thermodynamic state of material in extreme conditions.In many parameters of dynamic process,the equation of state of warm dense matter(WDM)at high temperatures and high pressures plays an important role.WDM is non-ideal,strong coupling,partially ionized,and partially degenerate.For the special status it is lack enough understanding.Both experiment and theory have enormous challenges.The key is how to solve the problem of generation,constraint,state diagnosis,characterization,and theoretical modeling of WDM.In this thesis,the noble gases argon(Ar)and helium(He)with a stable structure are chosen as the research object.Our work mainly focuses on experiments.By using multiple reverberation shock compression,dense gas Ar and He are compressed to warm dense state,and the equation of state parameters at high temperatures and high pressures are diagnosed.Combined the experiments with theoretical analysis,the thermodynamic,optical,and electrical properties of warm dense Ar and He are reasonable explained.This deepens the understanding of astrophysical evolution and fusion rule.Our major progresses are listed as follows:(1)The equation of state and transport parameter of warm dense plasma is the indispensable important data in astrophysical and fusion simulation.The state diagnosis of opaque plasma generated by multiple reverberation compression is a key problem.Based on the previous diagnosis target,we optimize to improve and perfect the target design composed of multi-layer composite windows.Combing with a Multi-Channel Optical Pyrometer,a Doppler Pins System,and a Streaked Optical Pyrometer,the optical radiation brightness history and the particle velocity profile history for Ar and He under shock compression are measured.The equation of state of opaque warm dense Ar with the pressure up to 160 GPa via 1-4 times compression,and warm dense He with the pressure up to 150 GPa via 1-10 times compression are obtained.This provides a scientific basis to examine the existing warm dense matter model and construct a new warm dense model.(2)Multiple reverberation shock compression can effectively improve the compression ratio.It can provide a reference for the dynamic compression properties of material.In our experiment,the shock wave is generated by the impact of flyer.In the condition of same work from outside,the internal energy increment of the system is also the same.But the ionization energy in different sample is distinguishing,and it leads to different atomic excitation and ionization.On the one hand,the atomic excitation and ionization absorb the heat energy in the system,and the compression ratio will increase.On the other hand,the ionization makes the particle number increase and it enhances the repulsion interaction between the particles.The compression ratio will decrease.Due to these two opposite process with partially offset,the compression ratio depends on the dominant extent.For dense gas Ar and He with the initial pressure of about 20 MPa and initial room temperature,when they are shock-compressed up to the same final pressure of about 150 GPa,the compression ratio is about 20 for Ar,and is about 35 for He.Thus,under the same condition,He is more easily compressed than Ar.(3)The radiation spectrum diagnosis with high time-spatial resolution is established and evaluated.The time-resolved spectra for multiple shock temperatures are of great significance.For the optical radiation intensity of He with large dynamic range change,how to realize the whole record of high time-spatial resolution spectra and the estimate between the temperature and radiation intensity.This is crucial to provide the parameter setting for the spectrometer and the streaked camera.For this purpose,we explore and analyze the streaked camera trigger timing,the scanning time,the exposure intensity,and so on.At present,the trigger device and intensity forecast have been effectively solved.The whole multi-shock radiance spectra with good signal noise ratio have been measured.The time-resolved spectra and the optical radiation history from the pyrometer are able to check each other.(4)In astrophysics,constructing the stellar evolution model is closely related to the material opacity.The calculated results of the opacity are discrepant due to the different theoretical model by considering the physical mechanism.Also the opacity is related to the material state.In this experiment,according to the optical radiance intensity history of shocked He,it is difficult to distinguish the compression process between the 2th and 3rd times directly,and it shows current He become opaque after second shock compression(the corresponding density of about 0.3 g/cm3 and the temperature of about 1 eV).By using free electron Drude model,the ionization degree and the electrical conductivity of He are calculated.The results show that the current region is in a weakly ionized and semiconducting fluid state,and dense He was compressed to the semiconducting fluid with low mobility electrons.The transformation from transparent insulator to opaque semiconducting fluid under shock compression is observed,which is consistent with the McWilliams' results(PNAS,2015).This can provide a reference for White Dwarf stars with opaque helium atmospheres.(5)Based on our experiments,the electron energy gap of dense Ar and He are analyzed by the experimental internal energy change,and the electrical conductivity of warm dense Ar and He are estimated by the fluid semiconductor Mott theory and free electron Drude theory.The results show that the lower initial density refers to the higher specific internal energy increment,and the corresponding energy gap is lower and the conductivity is higher.The conductivity of warm dense Ar under multiple compression is in the region of 103-105(ohm m)-1,where the ionization degree of Ar is higher.It indicates that current Ar is partially or completely conductive.Compared with the calculation of the Comptra04 program,our conductivity is lower.For warm dense He,the highest conductivity in our experimental state is about 103(ohm m)-1,and the current He is in a weakly ionized semiconducting fluid state.This is consistent with the conclusion of opaque He under multiple shock compression.