1. GEM tests at BNL Zvi, Sasha, Ilia and others

2. Triple GEM detector tests Last Tuesday after HBD meeting we exchanged CF4 by Ar/CO2 but still there were no signals. Then we started to check every swagelok and found the leaks. After fixing the problem we have seen the signals in Ar/CO2 but in order to get the gain of ~5000 in Ar/CO2 we had to go to dV=430V!!! The GEMs inside the vessel were socalled “Thanksgiving” GEMs. Nevertheless we decided to switch to CF4, raised voltage to 550V and again no signals. Then I decided to go back to Ar/CO2 to check whether there are still the signals at least at that gas. Yes, the signals were there. I left it overnight and in the morning recognized that the gain increased by ~50%. We again started CF4 flow and increased the voltage till 570V and only then we started to see some very low signals of the order of 5-6 mV. At this point we thought that probably there is something wrong with these GEMs and decided to exchange by “Hanuka” GEMs. Raise the voltage, the same. Then we checked CAEN N126 PS and it turned out that it was delivering 20% less voltage than you asked!!! We scaled the voltage by 20% and the signals! The gain was ~5000 at dV=508V. So I left it over night and ask Zvi to bring some more GEMs. In the morning Zvi brought 4 GEMs: as Zvi told these GEMs were tested on the laminar table and showed some current. So they never seen the glovebox. We installed triple GEMs detector (the 4 th one has a scratch, looks like knife). We checked all 3 GEMs in CF4, 2 were fine, the 3 rd one showed the current of the order of ~100 nA at 500V but going down. We waited till went to 0 and then ramped it to 550V. Then RC, some problems with the mesh and finally one of the GEMs showed a short, that was already Friday night.

3. Summary Although we lost many days fighting with these stupid problems like connectors, leaks, CAEN PS etc we successfully operated two triple GEM stacks: 1.“Thanksgiving” GEMs: these GEMs I sent from WIS to BNL and they never been at SB. 2.“Hanuka” GEMs: these GEMs were tested in quadruple GEM stack at SB and now in triple GEM detector at BNL.