Characterization Technology And System Of Inertial Confinement Fusion Target

In the ICF(inertial confinement fusion)system,the target is the core where all laser beams converge to induce nuclear fusion.To achieve the implosion condition,parameters of the shell and the ice-layer of the target should be strictly controlled.In that case,the implementation of its quality control is very important to the ignition.A critical step in the characterization of target is the precise determination of the refractive index and thickness of the layers.This thesis studies an iterative algorithm based on optical path difference(OPD)and ray deflection to obtain the ice-layer refractive index and thickness of the ICF target simultaneously;a compact,snapshot and triple-wavelength system is proposed for the target in-situ characterization;the proposed iterative algorithm is further improved to obtain the refractive index of the shell and the ice-layer simultaneously;a method based on the phase-shifting interferometry and ray tracing is proposed to obtain the 2D(two-dimensional)refractive index distributions of the shell/ice-layer at three wavelengths(532 nm,785 nm,1064 nm),from which the 2D density distribution of the layer is got.The main research contents and innovation results are as follows:1.An iterative algorithm based on OPD and ray deflection(IAORD)is proposed to obtain the ice-layer refractive index and thickness of the ICF target simultaneously.Starting from an assumed initial value,the refractive index and thickness are solved back and forth until the iteration stopping criterion is reached.Simulations show that the relative retrieval error of the ice-layer refractive index is better than 0.05%after finite iterations,and that of the thickness is better than 0.1%.While the relative retrieval error of the shell refractive index is better than 0.7%after finite iterations,and that of the thickness is better than 1.1%.Experiments show that the target shell refractive index and thickness can be retrieved with a relative error below ±2%.2.A compact system for testing ICF target shell/ice-layer refractive index and thickness simultaneously and in-situ at triple-wavelength is proposed.The system has been improved to adapt to the requirements of in-situ characterization of the target in the vacuum environment and engineering practice.The lateral resolution of the system is better than 2?m.Experiments show that a relative error below 2.1%is achieved for the target shell refractive index and thickness measurement,which is consistent with the simulated values of 2.19%for the refractive index and 1.09%for the thickness obtained from the test uncertainty analysis.The test uncertainty analysis also shows that the uncertainties of the ice-layer refractive index and thickness are 1.42%and 5.04%respectively.The system has the advantages of simple device,in-situ characterization,fast detection speed,high precision and high resolution,which poses great potential on the in-situ measurement of the ICF target.3.The IAORD is investigated in detail,and an advanced version(AIAORD)is proposed to obtain the refractive indices of the shell and the ice layer of the ICF target simultaneously.The concept of the fixed-point iteration and the cobweb graph are introduced in the advanced algorithm,and it is found that the right choice of the combination of the input values and the characteristic curves is the key to ensure convergence in the iteration.Simulations show that AIAORD is versatile and suitable for the applications with any two unknown target parameters to be solved.The test uncertainties of the index measurement are analyzed by simulations,and they show that the uncertainties of the refractive indices of the shell and ice layer are 9.78%and 1.10%,respectively.It can be found that the AIAORD has a good performance on measuring the refractive index of the ice layer when both the refractive indices of the shell and the ice layer are unknown.4.A method based on the phase-shifting interferometry and ray tracing is proposed to obtain the 2D refractive index distributions of the shell/ice-layer at three wavelengths(532 nm,785 nm,1064 nm),from which the 2D density distribution of the layer is got.A differential method is utilized to get the reference refractive index,based on which the refractive index distribution of the layer is retrieved.For targets with uniform refractive index in the ice-layer,simulations show that the relative retrieval accuracies are better than 10 ppb.For targets with nonuniform refractive index in the ice-layer,the optimal selection of the two rings on the wavefront map that yields minimal uncertainty to the reference refractive index is discussed.Experiments show that the refractive index distributions have good consistency at different wavelengths for the same target.The detectable normalized RMS(root mean square)of the refractive index distributions is at least 2.9E-4.The relative accuracies of the average refractive indexes of the shells are better than 1.5%for all three wavelengths.It is concluded that the proposed method and system poses great potential in the in-situ measurement of the refractive index and density distribution of the ICF target layers.