Research On Position Encoding Readout Method For Micro-pattern Gas Detectors

Due to the good spatial resolution,high rate capability,large active areas and radiation hardness,Micro-pattern Gas Detectors(MPGDs)are widely used in many applications such as particle physics experiments,nuclear science and medical imaging.Most of the readout techniques employ a large number of electronics channels to readout directly.The requirement of a large number of electronics channels has become an issue to the further applications of MPGDs,and poses a big challenge for the integration,power consumption,cooling and cost.Consequently,how to reduce the electronics channels is an urgent problem need to be solved,and also is a research hotspot.By changing the arrangement or structure of the readout electrode and multiplexing the readout channels with appropriate rules,position encoding readout can significantly reduce the number of readout channels and such work has been started in some research group.Based on the researching the readout methods of MPGDs,this thesis deeply studied two different position encoding readout methods,including the induction encoding readout and the direct encoding readout.The two position encoding methods are demonstrated by the Eulerian path of graph theory.A standard rules for encoding is provided,and general formulas of encoding&decoding for n channels are derived.Under the premise of such rules,a robust decoding algorithm is proposed,and then the charge gravity method is used in the algorithm to increase spatial resolution.Besides,the one-dimensional position encoding readout circuit boards and two-dimensional position encoding readout circuit boards were designed based on a 5×5 cm2 Thick Gas Electron Multiplier(THGEM).In the last part,using two different readout electronics,the verification tests were carried out on a 8 keV Cu X-ray source with 100?m slit.The test results show a robust feasibility of the position encoding readout methods,and have a good spatial resolution and linearity in its position response.The method can dramatically reduce the number of readout channels,and has an attractive potential to build large area detectors and can be easily adapted to other detectors like MPGDs.Inevitably,the method has some disadvantages,such as lowering the signal to noise ratio(SNR)and lowering the detector's rate capability.This thesis is arranged as follows:In chapter 1,the background information for MPGDs has been introduced.Firstly,three most mature MPGDs,including MicroMegas,GEM and THGEM,was selected and illustrated their principle and application.Secondly,described the readout signal feature and performance parameter of MPGDs.At last,generalized MPGD's readout methods and provided several methods which could reduce the number of electronics readouts.In chapter 2,the principle of two position edcoding readout methods has been illustrated,and its encoding method and decoding algorithim are discussed in detail.Firstly,we introduced the current research status of the position encoding readout method.Secondly,we explained the principle of induction encoded readout method and provided its two different encoding rules,and generalized the enconding&decoding formula for n channels readout.Thirdly,explained the principle of direct encoded readout method and provided an extensible encoding rule,and also presented a encoding&decoding formula for n channel readout.Based on the encoding rules,a robust decoding algorithm is proposed,and the charge gravity method is used in the algorithm to increase spatial resolution.Finally,we summarized the features and electronics requirements of the two position encoding readout methods.In chapter 3,several position encoding readout designs base on a 5x5cm2 THGEM are described.Firstly,the feasibility simulation of induction encoding readout is shown.According to simulation results,we designed a one dimensional gouping encoding induction readout board and discussed the fesibility of two dimensional encoding induction readout.Secondly,we designed a 1D direct readout board and two 2D direct readout boards with different resolution,and presented the corresponding encoding rules and decoding algorithm.Thirdly,we presented the design of multi-channel signal generator for verification test of encoded readout.Finally,the readout electronics for MPGDs is investigated,and briefly introduced two readout electronics for verification test of the position encoded readout method.In chapter 4,the verification test was described.Firstly,the test requirements are analyzed and a test plan is provided.Secondly,the X-ray test result is shown,such as single event verification,spatial resolution,postion scanning and 2D imaging;Finaly,discussded the test result.Finally,in chapter 5,we summarized the whole work and proposed an outlook.