Research On The Spatial Resolution Performance Of The Pulse-dilation Framing Camera

The pulse-dilation framing camera is the two-dimensional ultrafast diagnostic device that combines pulse-dilation technology with MCP framing camera,which is widely used in Inertial Confinement Fusion diagnostic experiments because of its picosecond-level temporal resolution and micron-level spatial resolution.The diagnostic data acquired by the camera is used as the key basis for studying the stability of ICF combustion and improving the energy gain of ICF.With the continuous breakthroughs of ICF research in recent years,not only is the framing camera required to have a temporal resolution better than 30 ps or even faster,but also needs to have a large detection area and high spatial resolution performance,which can achieve fusion burn phase detection with a duration of approximately 100 ps.Therefore,in order to meet the requirements of the ICF diagnostic experiment,the pulse-dilation framing camera is taken as the research object,and the magnetic focusing imaging system is designed under the premise that the temporal resolution is better than 10ps,and the influence of physical parameters on spatial resolution performance is analyzed,and the method of improving the detection area of the pulse-dilation framing camera and the overall spatial resolution performance of the Gaussian image plane is studied by optimizing the physical parameters.The main work of the article includes:（1）The temporal resolution research model of pulse-dilation framing camera is established based on the principle of pulse-dilation and the working principle of the framing camera.And the optimal physical and technical parameters of the 10 ps pulse-dilation framing camera is constructed by analyzing the relevant factors which affecting the temporal resolution;The picosecond pulse generator is designed by adopting Marx circuit with avalanche triodes and pulse steepening circuit,which obtains a dilation pulse with rising slope of 5.54 V/ps,and a gating pulse with amplitude of-2.7 k V and full width at half maximum of 198 ps.When the drift area is 400 mm and the cathode voltage is-3.75 k V,the pulse-dilation framing camera with temporal resolution of 8.6 ps is achieved;（2）The visualized magnetic focusing pulse-dilation framing camera space resolution research model is established by the physical modeling software COMSOL based on the finite difference method,magnetic scalar potential method,Monte Carlo photoelectron emission theory and axisymmetric magnetic field imaging theory.The evaluation method for the overall spatial resolution and uniformity of the Gaussian image plane is constructed,by analyzing the variation relationship of the spatial modulation transfer function between off-axis object points on the Gaussian image plane;The standard deviation is used to quantify the degree of deviation between the ideal imaging surface and the Gaussian image plane by analyzing the field curvature characteristics of the magnetic focusing imaging system,and the research method of the optimal overall spatial resolution performance is obtained based on the dynamic imaging magnetic field;（3）The spatial resolution and uniformity of the Gaussian image plane,the spherical aberration,field curvature and distortion of the imaging system are used as evaluation indicators,and the influence of parameters such as the number,position,leakage magnetic slit and aperture of the magnetic lens on the spatial resolution performance of the pulse-dilation framing camera is analyzed.When the drift area is 400 mm and the cathode voltage is-3.75 k V,and the imaging system is designed with three magnetic lenses with an axial width of 100 mm,an aperture of 220 mm and an leakage magnetic slit of 30 mm,the10 ps pulse-dilation framing camera’s detection area can reachΦ70 mm（radius is 35 mm）,the overall spatial resolution and uniformity of the Gaussian image plane are better than 3lp/mm and 167%,and the spherical aberration of the imaging system is 47.40μm,the imaging distortion rate is 2.27%,and the maximum curvature of field curvature is 0.015mm^-1.The main innovations of the article include:（1）The temporal resolution research model of pulse-dilation framing camera is established,the picosecond high-voltage pulse circuit was designed by using the Marx circuit with avalanche transistor and the pulse steepening circuit,and the optimal physical and technical parameters of the pulse-dilation framing camera with the short drift region is constructed by analyzing the influence of cathode voltage,drift area length,dilating pulse slope and MCP framing camera temporal resolution on the pulse-dilation framing camera temporal resolution.It provides a theoretical basis for the development of 10 ps pulse-dilation framing camera with short drift region.（2）The evaluation method of the overall spatial resolution of the Gaussian image plane is studied by analyzing the relationship between the spatial modulation transfer function curves of off-axis object points,and based on the physical meaning of the maximum relative error,the quantification of the spatial resolution uniformity of Gaussian image plane is achieved by analyzing the modulation difference between the off-axis object points;The standard deviation is used to quantify the overall deviation between the ideal imaging surface and the Gaussian image plane,and the method of obtaining the optimal spatial resolution and the optimal imaging magnetic field of pulse-dilation framing camera is studied under dynamic imaging magnetic field;（3）The 10 ps pulse-dilation framing camera imaging system is designed using short magnetic lens with large aperture and wide leakage magnetic slit.Based on the performance indicators such as spatial resolution and uniformity of the Gaussian image plane,spherical aberration,field curvature and distortion of the imaging system,a pulse-dilation framing camera with large detection area is achieved by analyzing the influence of imaging system parameters on the spatial resolution performance indicators,which provides a new idea for the research of pulse-dilation framing camera with large detection area.