【摘要】：隨著航天技術(shù)的發(fā)展，傳統(tǒng)的衛(wèi)星導(dǎo)航系統(tǒng)越來越不能滿足需求，在功能上呈現(xiàn)出一定的局限性。為了打破這一局限，近些年各航天大國對下一代導(dǎo)航系統(tǒng)—X射線脈沖星導(dǎo)航系統(tǒng)，投入了大量的人力、物力資源進(jìn)行研究。本文在調(diào)研國內(nèi)外探測器研究與應(yīng)用發(fā)展的基礎(chǔ)上，對應(yīng)用于X射線脈沖星導(dǎo)航系統(tǒng)的探測器性能需求進(jìn)行了分析，并重點(diǎn)研究了用于導(dǎo)航的MCP空間X射線探測器。 在進(jìn)行X射線脈沖星導(dǎo)航空間搭載試驗和未來脈沖星導(dǎo)航系統(tǒng)實際應(yīng)用之前，必須在地面搭建實驗?zāi)M系統(tǒng)，對探測器進(jìn)行全面的實驗測試與標(biāo)定，例如量子效率、探測效率、光子到達(dá)時間精度、脈沖輪廓的累積時間、定位精度等的計算。要標(biāo)定探測器首先要有一個已知光子流量的X射線源，并且該射線源的能譜具有良好的單色性。此外，X射線源的光子流量可以根據(jù)測試需求進(jìn)行調(diào)節(jié)。根據(jù)實驗需求，對課題組研制的用于標(biāo)定測試探測器的X射線源。該X射線源能夠產(chǎn)生七個單色能量的射線，分別是1.49keV、4.51keV、5.41keV、6.4keV、8.05keV、15.77keV、17.48keV。在真空環(huán)境下，用SDD探測器測試標(biāo)定了X射線源的最佳預(yù)熱時間、光子流量穩(wěn)定度、能譜分布、模擬脈沖輪廓特性，并通過改變X射線源到探測器的距離、燈絲電流和陽極高壓，對每一個能量下的X射線光子流量進(jìn)行了測試標(biāo)定，為后續(xù)探測器的探測效率的測試標(biāo)定奠定了基礎(chǔ)。 關(guān)于MCP探測器的研究本文重點(diǎn)從兩個方面進(jìn)行了研究： 一、為了提高探測器的探測效率，設(shè)計了復(fù)合式光電陰極結(jié)構(gòu)，主要工作內(nèi)容如下所述： 在對復(fù)合式光電陰極進(jìn)行實驗測試之前，仿真計算出探測器正常工作時的兩個電壓的最優(yōu)值：（1）采用CST軟件模擬計算出陰極電壓和MCP輸入電壓的電勢差在-300V時工作最佳；（2）為了提高探測器探測效率和探測的可靠性，優(yōu)化了收集陽極電壓V1。提高探測器收集陽極電壓可以減小電子云團(tuán)的直徑，，降低電子云團(tuán)發(fā)生交疊的概率，陽極電壓越高，電子云團(tuán)的直徑就越小，小到一定的尺寸后將不會變。通過計算可以得到電子云團(tuán)入射到收集陽極上時的半徑，計算結(jié)果顯示：當(dāng)收集陽極電壓在0V時，將電子云團(tuán)的半徑約為0.9mm；當(dāng)收集陽極電壓在-450V時，電子云團(tuán)的半徑為0.6mm，繼續(xù)增大收集陽極電壓至-800V，電子云團(tuán)的半徑變化很小，仍然約為0.6mm。根據(jù)這一計算結(jié)果可以確定收集陽極電壓-450V時最佳。（3）對復(fù)合式光電陰極的透射層碘化銫的最佳厚度采用兩種計算方法進(jìn)行計算，第一種是1981年漢克推導(dǎo)的計算模型，第二種是2011年胡慧君博士論文中推導(dǎo)出的計算模型，計算結(jié)果顯示，兩種算法下的最佳厚度值有一定的偏差。為了確定哪種計算方法可靠，用GEANT4軟件對不同厚度下的透射層碘化銫的量子效率和探測效率進(jìn)行模擬計算，通過模擬實驗獲知：采用第二種算法得出的厚度值是最佳的；為了進(jìn)一步確認(rèn)第二種算法的可靠性，計算光子能量一定時，不同厚度的透射層碘化銫陰極的量子效率和探測效率，計算結(jié)果表明，第二種計算方法得出的最佳厚度值是可靠的。 為驗證復(fù)合式光電陰極是否能夠有效的提高探測器的探測效率，制備了純反射式光電陰極和復(fù)合式光電陰極，并測試它們的探測效率。測試結(jié)果顯示：在相同的實驗條件下，復(fù)合式光電陰極的探測效率要高于純反射式光電陰極，分別可達(dá)到25.2%@1.49keV（透射層79.9nm+反射層1000nm）、14.2%@4.51keV（透射層144.35nm+反射層1000nm），而純反射光電陰極在相同的實驗條件下的探測效率分別16.2%@1.49keV（1079.9nm）、10.1%@4.51keV（1144.35nm）。 二、為了增大探測器的面積，初步對2×2陣列探測器進(jìn)行研究，重點(diǎn)是多通道共享陽極的研究。 首先，依據(jù)航天探測器設(shè)計的基本原則設(shè)計了2×2陣列的X射線探測器雛形用于實驗研究，并對各個零件進(jìn)行了選材工作。此外，從兩個方面對2×2陣列探測器進(jìn)行了優(yōu)化。 （1）提出了一種甄選性能一致的MCP的方法，該方法包括確立4個甄選關(guān)鍵參數(shù)、建立MCP可用標(biāo)準(zhǔn)、優(yōu)化實驗測試流程和實驗測試四個過程。 （2）研制出多通道共享陽極，通過減少讀出電子學(xué)通道數(shù)以降低大面陣MCP探測器電子學(xué)采集系統(tǒng)的成本、重量和功耗。分別對單通道陽極、雙通道共享陽極、和四通道共享陽極的脈沖信號傳輸性能進(jìn)行了模擬，模擬結(jié)果顯示這三種陽極在傳輸頻率低于0.1GHz的脈沖信號時波形無畸變、幅值無衰減、脈沖寬度無展寬，與實驗中用示波器觀察得到的結(jié)果相吻合。實驗表明：可以使用一個收集陽極和一路電子學(xué)來接收四個通道的信號，這樣使得探測器的電子學(xué)通道數(shù)目減少到原來的1/4，可以大大減小電子學(xué)系統(tǒng)的成本、重量和功耗。
[Abstract]:With the development of space technology, the traditional satellite navigation system can not meet the demand more and more, and has some limitations in function. In order to break this limitation, in recent years, the space powers have invested a lot of manpower and material resources in the next generation of navigation system-X-ray pulsar navigation system. On the basis of the research and application development of the external detectors, the performance requirements of the detectors used in the X-ray pulsar navigation system are analyzed, and the MCP space X-ray detectors used for navigation are mainly studied.
Before carrying out the space test of X-ray pulsar navigation and the practical application of future pulsar navigation system, it is necessary to build an experimental simulation system on the ground to test and calibrate the detector comprehensively, such as quantum efficiency, detection efficiency, photon arrival time accuracy, pulse profile accumulation time, positioning accuracy and so on. In order to calibrate the detector, we must first have an X-ray source with known photon flux, and the energy spectrum of the source has good monochromaticity. In addition, the photon flux of the X-ray source can be adjusted according to the test requirements. The optimum preheating time, photon flux stability, energy spectrum distribution, pulse profile characteristics of the X-ray source were calibrated by SDD detector in vacuum. The distance from the X-ray source to the detector, filament current and positive current were changed. The X-ray photon flux at each energy was measured and calibrated under extreme high pressure, which laid a foundation for the subsequent detection efficiency test and calibration of the detector.
The research on MCP detector is focused on two aspects:
First, in order to improve the detection efficiency of the detector, a composite photocathode structure is designed. The main work is as follows:
Before testing the composite photocathode, the optimal values of the two voltages in the normal operation of the detector are calculated by simulation: (1) the potential difference between the cathode voltage and the MCP input voltage is calculated by CST software, which works best at - 300V; (2) in order to improve the detection efficiency and reliability of the detector, the collecting anode is optimized. The higher the anode voltage is, the smaller the diameter of the electron cloud will be, and it will not change when it reaches a certain size. When the anode voltage is 0 V, the radius of the electron cloud is about 0.9 mm; when the anode voltage is - 450 V, the radius of the electron cloud is 0.6 mm; when the anode voltage is - 450 V, the collection anode voltage continues to increase to - 800 V, the radius of the electron cloud changes very little, still about 0.6 mm. The optimum thickness of the transmission layer of compound photocathode cesium iodide is calculated by two methods. The first one is the calculation model deduced by Hank in 1981 and the second one is the calculation model deduced by Hu Huijun in his dissertation in 2011. The calculation results show that there is a certain deviation between the two methods. The quantum efficiency and detection efficiency of the transmission layer of cesium iodide with different thickness are simulated by GEANT4 software. The simulation results show that the thickness obtained by the second algorithm is the best; in order to further confirm the reliability of the second algorithm, when the photon energy is fixed, the thickness of the different thickness is calculated. The quantum efficiency and detection efficiency of the transmission layer cesium iodide cathode show that the optimum thickness obtained by the second method is reliable.
Pure reflection photocathode and composite photocathode were fabricated to verify whether the composite photocathode can effectively improve the detection efficiency of the detector, and their detection efficiency was tested. The detection efficiency of pure reflection photocathode is 16.2%@1.49 keV (1079.9 nm) and 10.1%@4.51 keV (1144.35 nm) respectively.
Secondly, in order to increase the area of the detector, the 2 *2 array detector is preliminarily studied, with the emphasis on the study of multi-channel shared anode.
Firstly, according to the basic principle of spacecraft detector design, the prototype of 2 *2 array X-ray detector is designed for experimental research, and the material selection of each part is carried out. In addition, the 2 *2 array detector is optimized from two aspects.
(1) A method of selecting MCP with uniform performance is proposed. The method consists of four steps: establishing four key parameters, establishing available standards of MCP, optimizing experimental testing process and testing process.
(2) A multi-channel shared anode is developed to reduce the cost, weight and power consumption of the electronic acquisition system for large area array MCP detectors by reducing the number of readout electronics channels. The waveform of the pulse signal with transmission frequency less than 0.1 GHz is not distorted, the amplitude is not attenuated, and the pulse width is not broadened, which is consistent with the experimental results obtained by oscilloscope observation. The experiment shows that a collector anode and a circuit electronics can be used to receive the signals of the four channels, thus reducing the number of electronic channels of the detector to less than 0.1 GHz. The original 1/4 can greatly reduce the cost, weight and power consumption of the electronics system.
【學(xué)位授予單位】：中國科學(xué)院研究生院（西安光學(xué)精密機(jī)械研究所）
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TN966

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