Single Photon Imaging System Based On The Wedge Strip Anode Detector

There is a plasmasphere around the Earth, whose thickness is～10 times of the Earth's radius. The plasmasphere is composed of the abundant ions such as N⁺, O⁺, H⁺, He⁺, etc. It is a main way for studying the geospatial magnetosphere explosion by imaging the distribution of the He⁺ ion through its emission at 30.4 run. A Lunar Imaging Detection for the Earth's Plasmasphere will be carried out in the 2^nd project of Chinese Moon Program. Therefor, a prototype of "Single Photon Imaging System Based on Wedge and Strip Anodes Detector" has been proposed and developed with full independent intellectual property rights.The main contents, methods and achievements are presented as follows:1) Through the analysis and comparison between the Photoconductive and Photoemissive image sensors, the Anode Detector Based on MCP was proposed to the experiment of Lunar Imaging Detection for the Earth's Plasmasphere.2) A scheme of Single Photon Imaging System Based on WSA Detector was established by studying the WSA, Resistive Anode, Delay-line, Cross Strip, etc.3) A type of WSZ was chosen for the anode design through the analysis and comparison among the diverse electrode structures.4) A scheme for the overall system design was set up by studying the correlative theory of Single Photon Imaging. It was presented below:(a) A way of "Mercury Lamp + Diaphragm + Weakeners + Narrow-band Optical Filter of 253.7 nm + Optical Input Window + Imaging Mask + MCP" was used to simulate the single photon radiant source of 30.4 nm. (b) A windowless structure was chosen for the mainbody design. (c) Two MCPs were cascaded in a chevron mode. (d) The imaging charge was directly read out by the position-sensitive anode. (e) A way of "CSA + Gussian Shaping Amplifier + DAQ Card + MPU (Micro Processor Unit)" was applied for the electronic readout subsystem design.5) The correlative theory and technics were systematically studied. The formula of position decoding for the WSZ was deduced. The methods for revising the calculating errors caused by the interelectrode disturbances were studied. The effect of each parameter for WSZ on the imaging performance were analysed. Two simple and convenient methods of measuring the radius of imaging charge distribution were presented. A design method for the circular pattern of WSZ was studied. Two parameters for the circular pattern, the varation coefficient of strip width and the bottom wedge width, were optimized. An auxiliary program for the WSZ design was developed. Two technical ways, "Plating-incrassation after Photo-lithography" and "Photo-lithography after Plating-incrassation", were studied in detail and the former was chosen as the final technics.Two WSZ anodes have been fabricated with diverse electrode thickness: one was 1μm , and the other was 2μm. The rest parameters were same: the imaging charge collecting area wasΦ48 mm; the period width was 1.2 mm; the width of insulating gap was 30μm.6) On the bases of theoretical study and simulation, the CSA and Gaussian shaping amplifier were designed and fabricated.An architecture of multi-feedback infinite-gain high-pass filter was chosen for the CSA design and a N type JFET (Junction type Field Effect Transistor) was taken as the input stage of CSA. The shaping amplifier was composed of a pole-zero cancellation circuit, a two-stage Sallen-Key low-pass filter, and a pulse amplitude adjustment circuit.7) A software of data acquisition & processing based on the PCI-DAQ Card was developed.The software included a data acquisition module, a data processing module, and a digital image module. The communication mode between PCI-DAQ Card and host computer was of PCI bus-mastering DMA (Direct Memory Access). Four ping-pang buffers were configured in the host memory to answer for the continuous and high-speed data acquisition & processing by a pipelining mode. The data processing module carried out the main functions such as smoothing filter, peak detection, pulse amplitude discrimination, pulse pileup rejection, position decoding, event counting, and so on. The digital image module answered for exporting an integrated image with 256-level gray.8) An experimental system was set up in term of the scheme for the overall design and the primary technical indexes such as spatial resolution, linearity, counting rate, dark counting rate, and so on were tested. Additionally, the primary factors related to the imaging performance were analysed and studied.With proper evaluation, the system reveals an effective imaging area more thanΦ38 mm, a spatial resolution superior to 100μm, a nonlinear distortion less than 1% and a dark counting rate below 0.67 Hz/cm². It indicates that the developed prototype is up to the main technical requirements of the 2^nd Project of Chinese Moon Program for the EUV Detector.9) Some advices for the system optimization and the formal device development were presented by summarizing this thesis.