[Solid_gem] Minutes for March GEM monthly meeting

[liujianb at ustc.edu.cn]

Hi All,
 
Minutes from yesterday's GEM meeting have been attached to the meeting agenda and copied below
https://hep.ustc.edu.cn/indico/conferenceDisplay.py?confId=13
 
We saw a lot progress on large area GEM R&D at yesterday’s meeting.  
 
A large area GEM detector prototype built jointly by Tsinghua and IMP
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- GEM size : 45*45 cm^2, with 20 sectors on one side and a single sector on the other, GEM spacing: 2-2-2-2mm
- Hybrid readout board with pads and 1d/2d strips
- Process of the GEM prototype assembling was described in detail with a lot of pictures. Those interested can take a look at the slides posted on the agenda.
- Gain uniformity was tested of the prototype with F55. A uniformity of ~10% was observed for one pad readout area. 
- More tests will follow 
 
Tests of a large area GEM prototype at USTC
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- Tested the gain uniformity of a 30*30cm^2 GEM prototype and investigated the rather large gain fluctuations observed across sectors.  Mechanical deformations of the drift and readout boards caused by inaccuracy in machining of the GEM frames were finally found to be blamed. After fixing the deformations, the gain uniformity reached ~25%. 
- Measured absolute gain by monitoring the current drawn from the readout board when irradiating the GEM chamber with X-ray. The gain was measured as a function of high voltage for individual sectors. A good exponential relationship was observed between gain and high voltage. And a gain of up to 10^5 could be reached at 4400 V. It was commented, though, the measured gain seemed a bit too high compared to other similar measurements. 
- Spatial resolution studies are being prepared for the GEM prototype. 
- Building a even larger GEM prototype (of 0.5*1 m^2) is also planed.  
 
Progress in GEM foil production R&D at CIAE
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- Different formulas were tried for Kapton etching. An optimal one was identified which takes 40mins or so to reach 100% etching.  
- It is hoped to see a completely etched GEM foil in the near future.


Jianbei