[Solid_gem] minutes of September GEM monthly meeting

[Jianbei Liu]

Hi All,

All the slides presented at yesterday's meeting can be found on the meeting indico agenda now:
https://hep.ustc.edu.cn/indico/conferenceDisplay.py?confId=6

Below are the minutes I've put together of the meeting

Uniformity tests of the 30*30cm^2 GEM prototype using X-rays at USTC (Wenhao You and Zhouyi)
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- large spatial and time variations of X-ray energy spectrum still observed.  The time variations were found to be caused by unstable CO2 gas flow. And the spatial variations were likely due to non-uniform tension distribution over GEM foils. 
- after re-stretching GEM foils several times, many sectors got shorted and the whole GEM chamber stopped working. 
+ to do
  * change the CO2 flow control
  * clean GEM foils with ultrosonic bath
 
Progress on GEM prototyping and CASAGEM electronics at Tsinghua (Zhigang Xiao)
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 - a 45*45cm^2 GEM prototype is being stretched at IMP, readout PCB in making.
 - CASAGEM scaled up to 80 channels, to be tested with a small GEM chamber first, then with the large GEM prototype described above when it's ready.

 Status of the Italian electronics (with APV25) setting-up at CIAE
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- Many things tried. No reasonable results observed yet. Quite a bit frustrating. 
- trigger got lost when running DAQ
o No detailed information available about MPD. But it (plus HDMI-29) will no longer be used in the release of DAQ setup
o A final choice may be made between Italian electronics and SRS after the beam test that is  presently ongoing at Fermilab for the SBS full-size GEM prototypes made by UVa. It was however agreed that it would be always good to get the italian electrons to work at the 4 Chinese institutes regardless of whether the italian electrons will be picked as the final electronics.

Fabrication of  drift cathode and readout PCB and triple GEM simulation  at Lanzhou U. (Xiaodong Wang)
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- fabricated a few drift cathodes 
- made a readout PCB
  o  A plain PCB was glued to the back of the readout PCB to block the via holes in the readout PCB for gas tightness. Excessive glue was used causing too much glue to spread into the holes. This needs to be improved in the future.
- simulated a triple GEM using ANSYS and Garfield++. Preliminary results (electron drift, avalanche)  obtained.
 
Simulation of thermal neutron detection efficiency using GEM at CIAE (Chao Shan)
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- the neutron detection efficiency was simulated for various GEM configurations, coating materials and thicknesses of the coating materials. The optimum coating thickness  was obtained along with the maximum efficiency for the two coating materials of B and LiF, respectively. 

GEM work at UVa  (Yuxiang Zhao)
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-  showed the whole construction process of the large GEM prototypes at UVa in a great deal of detail with lots of pictures. Very good references to those building GEMs using the gluing technology. 
  o  Will continue to build 2 GEM chambers each month till early next year. Can host one or two Chinese collaborators every month who would like to get trained for large GEM fabrication.

Jianbei