Investigation Into The Mechanism And Shielding Design Of Electromagnetic Pulses Generated By Intense Laser Interacting With Solid Targets

Intense laser-target interaction is a complex physical process that generates energetic particles and rays that radiate electromagnetic pulses(EMPs)with amplitudes to MV/m and spectra to THz.The generation mechanism of EMPs is complex,difficult to describe by a single model,and seriously interferes with the normal operation of diagnostic equipment.Therefore,an in-depth study of the mechanism of EMPs generated by strong laser-target coupling and an electromagnetic shielding solution for the diagnostic equipment in the target chamber are the main problems that need to be solved in the field of EMPs generated by laser targeting.In this paper,a three-dimensional physical model of XG-III target chamber,target holder and internal diagnostic equipment is established,and the EMP signal and electron energy spectrum generated by high power laser targeting obtained from experimental measurements are used as excitation sources to study the regular characteristics of hot electron emission and neutralizing current radiation EMP,and a shielding scheme for diagnostic equipment and transmission lines is designed and verified on this basis.The main research contents and conclusions are as follows.(1)A model of electromagnetic pulses radiated by hot electron emission and neutralizing current is established,and the electron energy spectrum tested by the XG-III laser facility is used as the excitation source to study and reveal the contributions of the hot electron emission process and neutralizing current to the electromagnetic pulse radiation,respectively.The results show that the electromagnetic radiation generated by the neutralization current decreases significantly with distance;the law that the picosecond laser energy and the number of emitted electrons is the main influencing factors of the electromagnetic pulse is revealed.(2)The neutralization current generated by the target rod in the XG-III laser facility was measured by a ring current probe,which was used as the excitation source to explore the influence mechanism of the target holder configuration on the radiation characteristic of the EMP induced by neutralizing current.The simulation results show that the EMP generated by the straight holder is 48.42 k V/m,while the spiral holder is twice as low;the current path length of the target holder is inversely proportional to the EMP amplitude;the EMP amplitude generated by the neutralizing current is reduced to 12.25 k V/m and8.64 k V/m by optimizing the embedding of the spiral target holder into the conductive straight holder and plate,respectively.(3)A shielding box adapted to Thomson spectrometer is designed,and the electromagnetic radiation characteristics around and inside the shielding box are measured and analyzed in the XG-III laser facility,and the results show that the electromagnetic pulse in front of the shielding box reaches 79.1 V,while the internal one is 10.4 V.The simulation results show that the main frequency of the signal inside the shielding box is the same as the resonant frequency of the shielding box,and the shielding box can prevent the electromagnetic pulse leakage.By filling the bellows with absorbing material and placing lead layer in front of the shielding box,the EMP inside the shielding box is significantly reduced,and comparing the collision current of the shielding box before and after strengthening the shielding,it is found that the charge accumulation caused by the hot electron collision with the shielding box wall is the main source of EMP.Using the experimentally measured EMP signal as the excitation source,the cable crosstalk problem of EMP signal coupling is studied,and it is found that the crosstalk signal amplitude is inversely proportional to the cable spacing and length through simulation,and the copper foil wrapped cable can significantly attenuate the crosstalk signal.The results help to deeply understand the mechanism of electromagnetic radiation generated by laser targeting and provide experimental ideas and theoretical support for the design of electromagnetic shielding of large laser facilities.