Structures In High-Energy-Density Plasmas

Recently, high-energy-density physics (HEDP) has become an active area of research that receives considerable attentions. Progresses in theories have cast new lights on many HED phenomena. Developments in experimental techniques, such as ultra-intense lasers, pulsed power techniques and various advanced di-agnostics, enable us to create certain HED systems in laboratories, to detect processes occurred under HED conditions, and to estimate physical mechanisms responsible for some astrophysical phenomena far away in the universe. High-energy-density physics research has no only scientific significance, but also po-tentials of future applications. From the view of thermal and statistical physics, one important characteristic of HED systems is that they are usually under non-equilibrium conditions. Structures or modes often appear in systems under such conditions. Since the appearance of structures and modes is a common phe-nomenon in high-encrgy-density systems, investigation in this phenomenon is of considerable importance to get a deeper understanding of HED processes.Based on the reasons mentioned above, in this thesis we study the spon-taneous magnetization and surface charge density modulation mode selection processes in plasmas under high-energy-density conditions, as well as the effects of such structures and modes on relevant HED processes. We hope to provide new insights for certain HEDP problems and reference in relevant researches. The main topics and results contained in this thesis are as follows:1. The possibility of spontaneous magnetization in plasmas under high-energy-density conditions has been discussed. A quasi-static model is developed for qualitative calculations. By using a dynamic model, we investigated the responses of HED plasmas to interior statistical fluctuations. The temperature-density phase diagram for spontaneous magnetization of plasmas is obtained through these qualitative calculations and quantitative solutions of model equa-tions, indicating that the spontaneous magnetization process is possible, at least theoretically. Further more, we discussed the appearance of common cosmic magnetic fields and proposed a novel explanation for the origin of the large-scale magnetic field structures in the universe. We also discussed the relation between the inflation phase and the cosmic magnetic fields and gave a new energy source for the inflation.2. The mode selection of plasma surface under high-energy-density condi-tions has been investigated. We first discussed the evolution of one-dimensional electron systems under HED conditions by the least-action principle and variation method. Assuming that charge density modulations are basic modes and choos-ing the amplitude and spatial wavelength of these modes as general coordinates, we obtained the equations of energy conservation and force balance. Numerical solving these equations gives the temporal dependence of amplitude and spatial wavelength of the modes. We also discussed the mode selection of plasma surface in two-dimensional case, using fluid equations of plasma and eigen-mode method. The dispersion relations of surface charge density modulation modes have been obtained.3. The effects of structures or modes of high-energy-density plasmas on certain processes have been researched. In the case of generation of electron beams through ultra-intense laser-plasma interaction, we discussed the effect of magnetic field on the divergence of electron beams through theoretical analysis and classical trajectory Monte Carlo simulations. Results show that self magnetic field of electron beams has non-negligible influence on the their divergence. After including both electric and magnetic field in our consideration, our results are in good agreement with experiments. In the case of oblique incident intense x rays on metallic targets, we discussed the possibility of the generation of surface Compton current density, as well as electromagnetic pulse due to this current density. Theoretical analysis reveals that such surface Compton current density could generate strong electromagnetic pulses, and this mechanism might be of considerable importance in the generation of electromagnetic pulses.