Development of a prototype GEM TPC with a gating grid for an H-dibaryon search experiment at J-PARC
Development of a prototype GEM TPC with a gating grid for an H-dibaryon search experiment at J-PARC
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开发带有门控网格的原型 GEM TPC，用于 J-PARC 的氢二重子搜索实验
DOI：
10.1016/j.nima.2014.06.007
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
K. Tanida et al.
中科院分区：
文献类型：
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作者：
H.Sako;K. Tanida et al.
我们开发了一个基于 GEM（气体电子倍增器）的原型 TPC（时间投影室），带有门控网格，用于 J-PARC 的氢二重子搜索实验。为了研究其性能，我们进行了实验室测试和使用Ar–CH 4 (90:10)和Ar–CF 4 (95:5)两种气体的束流测试，其中前者主要用于测试。在光束速率高达 5× 10 5 cps cm 2 （每秒计数）时，每行焊盘的命中检测效率经测量为 98%，在 3× 10 6 cps/cm 2 速率下为 90%。基于在漂移长度 5–20 cm 处测得的水平分辨率为 0.19–0.46 mm，估计在 1 T 磁场中水平位置分辨率优于 0.3 mm进行最后的实验。测量离子回流分数为 5%，并通过调整 GEM 电压配置（增益为 1.6× 10 4）将离子回流分数降低至 3%。在高达 5× 10 5 cps/cm 2 的束流速率下，由于门操作中的离子回流而导致的水平位置失真被抑制在 0.2 mm 以内，对应于高达 2.7× 10 8 s− 1 cm− 1 的离子回流。另一方面，测得浇口打开时的变形为1.3mm，对应于1.3×10 9 s−1cm−1的回流。最终实验中的变形估计为0.3±0.2mm，在1mm的要求之内。 GEM 在与最终实验相当的时间内连续运行，单位 GEM 面积的平均能量沉积率是实验预期的 30 倍。
We have developed a prototype TPC (Time Projection Chamber) based on GEMs (Gas Electron Multipliers) with a gating grid for an H-dibaryon search experiment at J-PARC. To investigate its performance, we conducted laboratory tests and a beam test with two kinds of gases, Ar–CH 4 (90: 10) and Ar–CF 4 (95: 5), where the former is mainly used for the tests. The hit detection efficiency per pad row was measured to be 98% at the beam rate up to 5× 10 5 cps cm 2 (counts per second), and 90% at the rate of 3× 10 6 cps/cm 2. Based on the measured horizontal resolution of 0.19–0.46 mm at the drift length of 5–20 cm, the horizontal position resolution of better than 0.3 mm is estimated in 1 T magnetic field for the final experiment. The ion backflow fraction was measured to be 5% and reduced up to 3% by tuning the GEM voltage configuration, at the gain of 1.6× 10 4. The horizontal position distortion due to ion backflow in the gate operation was suppressed within 0.2 mm at the beam rates up to 5× 10 5 cps/cm 2, corresponding to the ion backflow up to 2.7× 10 8 s− 1 cm− 1. On the other hand, the distortion with the gate open was measured to be 1.3 mm, corresponding to the backflow of 1.3× 10 9 s− 1 cm− 1. The distortion in the final experiment is estimated to be 0.3±0.2 mm, within the requirement of 1 mm. The GEMs have been operated continuously for a comparable period of the final experiment, with average energy deposit rates per unit GEM area of 30 times as high as that expected for the experiment.