| The fusion energy produced by laser Inertial Confinement Fusion(ICF)has the advantages of clean,efficient and controllable,which has become one of the important frontier research fields in international nuclear physics.According to Lawson's criterion,it is necessary to ablate and compress the target in order to realize the fusion reaction successfully,but a large number of hot electrons will be produced in this process,which will induce the strong electromagnetic pulse(EMP)radiations.The energy of these electromagnetic radiations is large and the frequency band is wide,which will not only interfere with the physical experiment in the process of shooting,but also cause damage to the precision diagnostic equipment.Therefore,it is of great theoretical significance and practical value to reveal the key factors that affect the characteristics of electromagnetic radiation produced by the coupling of high-power laser and targets,and to explore the generation mechanism.In this thesis,combined with the experimental measurement and simulation calculation analysis,the hot electron produced by high-power laser irradiation the target and the induced electromagnetic pulse are comprehensively analyzed.The relationship between the quantity,energy and distribution of the emitted hot electron and the intensity,direction and change rule of the EMP is established,and the mechanism of the EMP generation is deeply discussed by establishing the relevant model.The specific research contents and important conclusions are as follows:(1)the characteristics of the EMP generated by femtosecond laser incident on aluminum targets are studied and analyzed.The results show that: the radiation intensity and frequency band width of EMPs in target chamber and diagnosis cavity can be enhanced by applying a pre-ablation laser before the main laser.When the ablation laser is incident on the target 100 ps in advance,the strongest EMP signal can be obtained.The simulation results also show that the enhancement effect of the ablation laser on the energy and quantity of escaping hot electrons.Combined with the analysis of the "sin c" function,it is confirmed that the escaping thermal electrons are the main source of the electromagnetic pulse;(2)The radiation characteristics of the EMP generated by interaction between powerful laser and CH doped target are studied.The EMP generated after the picosecond laser incident on the CH target doped titanium is measured and analyzed on the XG-? laser device.It is found that the intensity of the EMP first increases with the increase of the doping amount from 1% to 12% and reaches the maximum at 7%.In order to further understand the law,we establish the target-holderground equivalent antenna model proving that the escaping hot electrons are the main source of EMPs,and obtain the spatial distribution laws of hot electrons and EMPs by simulating the electronic transport process.(3)The linear relationship between the radiation characteristics of electromagnetic pulses and the laser intensity is studied,and the protection scheme of the cable of the diagnostic equipment is preliminarily explored through the simulation.The cables are shielded with thin metal copper,and the distance between the cables is more than 5mm,which will further improve the antielectromagnetic interference performance of the equipment.The research results of this thesis will help to deepen the understanding of the mechanism of escaped hot electron and the EMP generation,provide experimental and theoretical support for the shielding design of domestic high-power laser,and provide new ideas for the development of high-energy EMPs. |
PDF Full Text Request