After the liquefaction of Monday, we observed a strong noise on the anode FE and on the micro-mesh electronics. Yuki and Tugdual investigated the reason of this noise, discovering by the way that a part of it was due to our primary pump and the noise was decreasing when gas pressure was higher and when voltage was lower. By the way, we decided Friday to cryopump the xenon to investigate our electronics noise without liquid. At this moment, we thank that the noise was perhaps associated to the fail of liquid xenon dropplets from the cold head.
After recovering 3 cm of liquid xenon by cryopumping, this strong noise has completely disapeared ! And when after, we filled back the liquid to the previous level (~ 20 cm for ~ 20 kg), the noise stayed at the low level.
So of course, I think something is not understood conerning this noise. It could be linked to the vaporisation process or to the gas line injection. It makes a lot of micro-waves, inducing by the way strong noise on our FE.
Friday afternoon, Yuki and Tugdual investigated the noise in this condition. It is now between 200 and 400 e/channel, but the noise contains a common contribution which is present on the 16 channels (due at least to the primary pump and to the vibrations induced by the PTR). We are now working to suppress this common contribution, hoping to reduce the noise level.
Monday, we will try to reduce the common noise by playing with grounds and the primary pump. After that, I think we will try to calibrate precisely the sensitivity of each channels with a gamma ray source with in addition, I hope, a first Compton reconstruction. It is now very exciting even if all can change fastly due to the problem we met the last week without successing to identify it.