Minutes of the forward endcap EMC eZuce SRN meeting, 18th of July 2016, 14:00-15:10

Presence:

• Basel: Werner
• Bochum: Cathrina, Claudius, Fritz-Herbert, Malte, Matthias, Miriam, Patrick, Stephan, Tobias H., Tobias T., Tom
• Bonn: Christoph
• Giessen: Hans-Georg
• Groningen: Myroslav
• Stockholm: -
• Uppsala: Pawel
• GSI: -

APD subunits:

• Summary of new insights into the '1:2 problem' (preamp output ratio of 2 of the two APDs of one crystal, seen on half of the crystals)
  • The unit showing both ratios of 1:1 and 1:2 in one cosmics run was found to be completely decoupled from the crystal
  • Looking at the event numer (aka time) one sees that the ratio started to be 1:2 at the beginning and soon turned to 1:1
  • A 'pressed coupling' of the APD unit against the crystal with the remaining silicon pad still attached to the APDs gives a read out ration of 1:1
• It seems that the 1:2 ratio problem is a coupling problem even though we are far from fully understanding what is going on
  • Does a perfect adhesive coupling give twice the light output of a coupling with the silicon just pressed to the crystal? (Measurements explicitly adressing this question are going on)
  • Why do we see ratios of 1:2 directly after a fresh glueing?
  • Why does it seem there are only tight coupled or totally decoupled APDs (no ratios in betwwen 1:1 and 1:2)? (There seem to be no 'partly' (de)coupled APDs)

APD preamps:

• There are about 170 VPTT preamps of one gain ready and tested that will be sent this week or next week
• There are also 32 APD preamps of the latest version ready to be sent

Radiation map:

• There was some discussion on how to proceed with getting detailed, realistic radiation maps
• It was agreed that Karoly, who started working on this, should go on with work on this topic
• Pawel has been in contact with Karoly as he needs information for further tests, awaits approximate values this week

ADC boards:

• Pawel needs information about the measured ratio between high and low gain in order to modify for a ratio of 1:16 (Malte will provide the Bochum results)
• We decided to leave all four different shaping constants implemented to the boards for the time being as we need to closer look at pulse shape stability
  • Myroslav pointed out that pulse shape stability is an important issue in the deconvolution of pile up events as the algorithms rely on stable shapes

HV adjustment boards:

• Christoph showed pictures of the latest PCB layouts
• There are mock-ups in the works to mechanically test for connectability, mounting sequence etc.
• For I2C cabling the barrel 'Bedea' cable seems to be probably not suitable (too tiny), Christoph will ask for a suitable cable w/ two differential lines plus one power line in a 3...4 mm overall diameter cable

HV module repair:

• We will send three broken HV modules to ISEG and await offers for repair.
• We will continue testing until all HV modules currently in Bochum have been screened

Irradiation of 'inner endcap wall' material candidates:

• Hans reported of 'plastic smell' at the end of an exposure to 1000 Gy of four different foam test pieces
• It is unclear what piece caused the smell
• He will send back the pieces to Bochum for evaluation of material deterioration
• Once we decided for a material we will need to test it at twice the dose as 1000 Gy may be a too short estimate for the inner walls