Research On Key Technologies Of Space UV Photon Counting Imaging Readout System

Currently,there is a growing demand for high-resolution and high counting rate observation of ultraviolet targets such as near-earth space and deep space in the field of space science.The detection system is required to have a high sensitivity level,capable of single photon detection due to the weak ultraviolet radiation intensity generated by the observation target.Furthermore,the counting capability of the photon counting detection system needs to be able to handle the rapidly increasing radiation intensity of ultraviolet bands during an observed target’s active burst period.Photon counting imaging technology based on Microchannel Plate(MCP)can make full use of the advantages of high gain,high spatial and temporal resolution of MCP,and has been widely used in the field of space ultraviolet observation.However,the position-sensitive anode and readout technology for two-dimensional imaging and radiation protection technology remain limiting factors in further improving the system performance.This paper focuses on optimizing the design and preparation of the position-sensitive anode,analyzing the electronic readout noise,counting error mechanism,and space radiation protection materials and structure shape,among other key technologies.The main research achievements include:(1)A three-dimensional structural model of a cross strip(XS)anode was established to investigate the relationship between the anode electrode capacitance and the anode material and pattern through finite element analysis.The inter-electrode charge crosstalk was represented using a cross capacitance matrix,and a charge correction method was developed.An XS anode design method was proposed with a three-layer superimposed structure.A 32×32 groups of electrodes XS anode sample was prepared using a printed circuit board(PCB)process.The experimental results demonstrated that the deviation between the electrode capacitance and the simulation results was less than 9%.The crosstalk between interlayer electrodes in the X and Y directions was lower than that between adjacent electrodes within the layer.The proposed three-layer structure is suitable for high-reliability space applications,and the total counting rate of the XS anode reached 600 kcps.The full width at half maximum in the X direction can reach 0.8mm.(2)The calculation method for equivalent noise charge(ENC)has been derived by combining the anode with the readout electronics.Two types of shapers,complex conjugated pole and real pole,have been designed,and the ENC values of different orders have been calculated.The complex conjugated pole shapers have shown better ENC performance than the real pole shapers.Based on this,the parameters of the charge sensitive amplifier(CSA)input transistor and the order and time constant of the shaper have been optimized,and a low-noise detection system has been realized.The experimental results have demonstrated that the optimized readout electronics ENC is reduced to 220 e-,which is much lower than the output charge of the detector and achieves the goal of a high signal-to-noise ratio.By adjusting the time constant of the complex conjugate pole shaper to 500 ns,the spatial resolution can be improved to5.657 lp/mm.(3)Circuit models were established for the anode and readout electronics in both time and complex frequency domains,and their impact on charge-induced readout time,CSA response time,and shaper time constant were analyzed.The research also proposed a counting error representation method for the entire system.The effects of anode capacitance,transistor transconductance parameters,and shaper time constant on system response time and counting error were verified through experiments.The stability of the analog shaper at high count rates was also discussed,and a pulse shaping method based on trapezoidal function was simulated.Finally,an adaptive trapezoidal shaping width method was proposed,which dynamically adjusts the shaping width with the input pulse interval to reduce counting and amplitude extraction errors.The photon counting detection system was tested,achieving a linearity of system count rate of up to 900 kcps and a spatial resolution of up to 4.490 lp/mm when the incident light intensity was 400 kcps.(4)Finally,the research used the Geant4 Monte Carlo application software package to simulate the interaction processes of electrons and protons with aluminum(ALU),high-density polyethylene(HDPE),and tantalum(TA).The results showed that at the same mass,TA and HDPE have better shielding effects on incident electrons and protons,respectively.The target received the lowest total ionizing dose(TID),which was 71% lower than the maximum dose,when the total equivalent aluminum thickness was 7 mm(0.7 mm for ALU,2.8 mm for TA,and 3.5 mm for HDPE).The shielding effect of three layers is significantly better than that of a single layer.A local protection structure with a finite boundary outer edge was proposed.This structure combines the equivalent range of charged particles in PCB to provide uniform thickness protection in all directions for each point inside the local box.The radiation protection structure of the detector was also studied,and an additional shielding ring was added to the most sensitive area of the input side wall of the detector to achieve lightweight protection.The findings indicate that the XS anode,consisting of three superimposed layers,offers a straightforward preparation process and facilitates achieving the optimal design of the readout electronics ENC.Its low distributed capacitance contributes to this advantage.Furthermore,the ideal counting error mechanism can enhance the counting capability of the system.The photon counting imaging technology can be more extensively utilized in space science by selecting an appropriate combination of multilayer shielding materials and a local shielding structure shape.