采用大面积GEM读出的TPC探测器研制

The time projection chamber(TPC) is a charged particle tracking detector. It can provide both 3D spatial coordinates and dE/dx for every track segment precisely, and has been widely used in experimental facilities with much success. As the traditional TPC’s read out methods, multi wire proportional chambers(MWPCs) have some weaknesses, such as it can only worked in on/off model for suppress the ion feedback when the track density is higher. This greatly limited the TPC’s maximum counting rate. A multi-layers GEM amplification stage offers a number of advantages: the homogeneity of the sensitive volume make it suited for read out with high granularity, E×B effects are strongly reduced, the electric field configuration provides intrinsic ion feedback suppression so the continuous operation is possible. The studies of the TPC using GEMs have attracted great interesting in decade, but the large area GEMs were used only in recent two or three years. Through our research, we can develop key technology for the purpose of improvement of our experimental facilities.

时间投影室(TPC)是一种径迹测量探测器，它可以测量带电粒子的连续的三维径迹和dE/dx能损信号。对于采用气体为工作介质的TPC探测器，被探测粒子的散射几率会大大降低，这一方面可以保证粒子径迹的测量精度，另一方面也减小了对后续测量的干扰，因此在许多大型的实验装置中都采用了TPC探测器来确定粒子径迹。目前已工作的TPC，大多数采用了多丝正比室(MWPC)作为端部放大器，而随着探测器技术的发展，一些新型探测器开始替代MWPC，其中GEM具有较为突出的优点，如灵敏区内各向同性、适合高密度读出、磁场引起的放大区径迹畸变(B×E效应)小等，另外多层GEM还可以有效的抑制正离子反馈，使得探测器可以工作在连续模式。大面积GEM读出的TPC探测器研究在国际上刚刚开始，获得相关的关键技术，对我们现有的探测器装置的升级改造或建造新的探测器装置都有非常重要的意义。

采用GEM读出的TPC探测器，由于结构简单，测量精度高的优点，受到人们的密切的关注。由于读出电子学成本的下降，原来只能应用于大型高能粒子物理实验的TPC探测器也可以应用在普通的一些小型核物理实验中。本项目通过理论模拟显示出GEM探测器的性能与电压有密切关联，优化电压可以提升探测器的性能。另外通过对TPC场笼电场的模拟显示，优化场笼设计可以提高电场的均匀性。本项目研制完成了一个45×45cm2的GEM探测器，测量显示该探测器具有较好的增益均匀性。同时本项目还建成了一个小型GEM读出的TPC探测器，通过激光对该探测器的测试显示其能量分辨为12%，漂移时间分辨为1ns，漂移方向的定位精度达到100微米。