| Time Projection Chamber (TPC) is a high precise tracking detector. It can provide both 3D spatial coordinates and particle tracks to get dE/dx information. With high?ability of particle identifying, it has been widely used in a lot of high energy physics experiments. At Tsinghua University, a TPC prototype based on GEM readout (named TU-TPC) was constructed successfully and has been proved with very good performance, providing a basis for future study and improvement.Drift field is very important to the performance of TPC detector, and there are two influence factors: one is the static electric field produced by Field Cage and the other is the dynamic electric field caused by space charge. Establishing a better static field is a most important task in TPC design, at the same time, the accumulation of space charge is inescapable, especially in TPC for HPLUS and PANDA, which have to obtain much higher spatial resolution and momentum resolution under high event rate. The high-rate colliding and no gating scheme used to suppress ion feedback will cause both the primary ions and the secondary ions drift back from the endplate accumulate heavily in drift volume, worsening the electric field there. The measurement of the distortion of the drift field and the calibration of the tracks reconstructed are significant. Based on the requirements for TPC improvement and the problem faced, this thesis focuses on the study of the influence of the electric field in TPC in order to get improved performance.To study and improve the TPC drift field, the followings were fulfilled: 1, Aimed at the design of the static field, the simulation of the initial electric field in TPC volume were accomplished in following conditions: Field Cages with one-side and double-side strips, with and without guard ring around GEM detector. The deviations of electron drift in static field for corresponding models were acquired with Garfield; 2, To calculate the dynamic field caused by space charge, according to Green formula to solve Poisson function, several Green functions for TPC geometry have been derived and employed, analytic equation has been provided, and potential and electric field intensity for space charge in unit region have been calculated, with simulation steps for space charge in TPC presented; 3, Through the comparison of the static electric field and the deviations of electron drift, the advantage and necessity of a Field Cage with mirror strips and a guard ring in proper position were foreseen; 4, TU-TPC was reconstructed and then modified with new schemes of Field Cage and guard ring, with performance test before and after modification, which verified the improvement of static drift field.The difference between the ionization position and the collecting position of electron was important for particle tracks calibration to get true tracks, therefore, with analysis methods for electric field in TPC drift volume basically completed, the calculation fundamental of electron drift deviation was searched. With a way proved feasible, the drift result in simple electric field was the same with the result got in Garfield, providing a maneuverable analytic way to calculate electron drift and convenient to import electric field. In the final part of the dissertation, several gas mixtures were studied to get the best choice for steady TPC performance, in term of space charge suppression.The accomplishment of this article will be important to improve and maintain the performance of TU-TPC, which is helpful to accumulate useful experiences for future GEM-TPC design and application in high-rate experiments as well.
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