X-ray Microscope Using Toroidal Mirrors Working At Grazing Incidence

Laser inertial confinement fusion?ICF?is one of the effective ways to realize the controlled nuclear fusion,which can provide technical support for sustainable energy production and military applications.The physics basis is to utilize the material inertia to achieve compression of the deuterium-tritium-filled capsules via focusing megajoule laser energy onto the hohlraum,and finally achieve thermonuclear explosion and continuous combustion.High resolution imaging diagnosis based on X-ray microscope can be used to reveal some important physical information such as the temperature and density of the laser-produced plasma,symmetry and uniformity of the driving source of the radiation,the implosion compressed plasma hydrodynamic instability growth,the temperature and yield of hot electron.All of these parameters play an important role in ICF diagnosis.Since the core region of the target is an extremely dense plasma,the hard X-ray is of extremely strong penetrating ability and thus cannot be absorbed,besides,the hard X-ray has the characteristics of not being influenced by electromagnetic field in the hohlraum,so it is the most suitable diagnosis technology for the target core area.Considering the small scale of plasma,it is necessary to establish a hard X-ray imaging system with micron scale resolution.At present,X-ray diagnostic equipment used in ShenGuang system includes pinhole and KB microscopes working in the soft X-ray band.They are difficult to be extended to the hard X-ray imaging while ensuring wide field of view and high resolution.According to the requirements of laser fusion diagnosis and in order to overcome the shortcomings of the current diagnostic equipment,the research of hard X-ray microscope based on toroidal mirrors working at grazing incidence was carried out,the paper mainly includes the following parts:?.The design and research of the X-ray microscope focus on the overall requirement for large field of view and high resolution.The toroidal mirror with different meridian and sagittal curvature radii is selected as the focusing optical element of the imaging system to replace the orthogonal sphere mirrors,in order to eliminate the reflectance loss of mirrors and make the system structure more concise.At the same time,the toroidal mirror is a cheaper alternative to the use of more expensive aspheric surfaces for the simplicity of its super-smooth surface fabrication is second only to the spherical mirror.By analyzing the focusing characteristics of toroidal mirror and double mirrors,the basic structure of two tandem toroidal mirrors in U-shaped arrangement and one planar mirror for spectrum selection is proposed,which is convenient to introduce more freedom into the optimization to solve the serious aberrations caused by the reflection of single toroidal mirror and improve field of view.By analyzing the requirements of X-ray total reflection,the relationship between grazing angle and reflectivity are studied,and the design of W/B₄C non-periodical multilayers is designed to meet the requirements of high reflectivity and large angle bandwidth.According to the requirements of the laser fusion diagnosis,the basic suitable parameters are put forward for ShenGuang?,and then based on triangle geometry and the stigmatic requirements,further calculation for the parameters of toroidal mirrors and optical structure is carried out.A simulation model of the initial structure based on ray tracing is established,then the rationality of apertures'location is analyzed and the effects of various parameters on the imaging quality are studied through ray tracing,and the constraint between the variables in the optimization function are determined.The imaging quality of the optimized microscope is significantly improved.?.On the basis of geometric aberration analysis,the spherical aberration,coma,astigmatism and field curvature of the meridional plane of the double toroidal mirrors were analyzed.The results show that by adjusting the mirror length and mirrors'spacing can eliminate some aberration,which can be used as reference in the optimization.According to the non-coaxial asymmetric structure of the grazing incidence optical system,the vector aberration theory is introduced for analysis.Based on the vector aberration of the coaxial reflection system,the vector aberration of the grazing incidence system is derived by means of pupil transformation,for the apertures and the field of view are off-axis.The fringe Zernike expansion terms of aberration are modified for the rectangular aperture,and each aberration of the microscope is analyzed by using the method of full field display of aberration,which makes up for the incomplete analysis of the aberration only from the sagittal and meridian plane.As for the evaluation of image quality,the spot diagram and geometric transmission function are used for they are more suitable for a large aberration system,and the results show that the object resolution can reach 5?m in±500?m field of view.?.The influence of the tolerance for the alignment errors and processing errors on the system imaging quality are analyzed,the parameters such as object distance,image distance,mirrors'displacement and tilt are firstly analyzed,the key optical components of hard X-ray grazing incidence microscope–toroidal mirrors'meridional curvature,the shape error and roughness are analyzed,and then according to the sensitivity of various parameters'influence on imaging quality by ZEMAX tolerance analysis,different weights of tolerance are assigned,take that 80%spot radius are less than 75?m as a standard,then adjust the tolerance,the final tolerance distribution were determined.?.In view of the difficulty of accurate positioning of aspheric mirrors caused by a series of factors,such as non-coaxial of the optical components of the imaging system,too small grazing angle and X-ray invisibility,a visible light assisted assembly system is designed to precisely adjust the grazing incidence angle during off-line assembly phase.Due to the fact that the incident optical axis and the outgoing optical axis of the grazing incidence system are parallel and not collinear,a bidirectional binocular intersection aiming system is designed for the online high-precision target aiming and accurate positioning of X-ray CCD.Through experiments,the spatial resolution of the imaging system is tested.The main reason why the simulation results are better than the experimental results is analyzed that the processing of the toroidal mirror cannot meet the ideal requirements.