Minutes of the forward endcap EMC eZuce SRN meeting, 4th of July 2016, 14:00-15:30

Presence:

• Basel: Werner (left soon because of bad connection)
• Bochum: Claudius, Fritz-Herbert, Malte, Markus, Matthias, Tobias H., Tobias T., Tom
• Bonn: Christoph
• Giessen: Hans-Georg
• Groningen: Myroslav
• Stockholm: -
• Uppsala: Pawel
• GSI: -

ADC read out:

• Bonn (Johannes) has been working on the adaption of their VHDL code to what we need for ADC readout
  
  • We will test it as soon as we get the ADC back from Sweden
  • The ADC board is still radioactive from the TSL beam time
  • As soon as it is manageable it will go to Stockholm for further performance tests, will be modified according to what we need (input range, gain ratios) and then will be sent to Bochum (in about two weeks from now)
    • We will provide gain ratio measurement results
    • Where did the ringing come from we observed in Bochum? There is no ringing showing up in the TSL beamtime measurements (w/o preamp/detector coupled to the ADC board). Does the ringing show up w/ connected preamp only (-> test in Stockholm)?

Glueing of photo detectors to crystals:

• We need to modify our glueing procedure
  
  • We need to test different methods (cleaning fluids, primer) on real PWO material with comparable stresses.loads.torques on the couplings
  • Malte presented a plot of a measurement on a recently reglued APD-unit that was fallen off its crystal: The ratio plot showed both ratios 1:1 and 1:2! This is the first time we observe this behaviour... (On Tuesday the unit was found to be fallen off the crystal!)

APDs:

• Matthias presented some strange results of an APD screening measurement:
  • There seems to show up some saturation effect causing non linearities even in the some uA-current range: The lower you set your (DC) light source the higher is the resulting gain
  • As we will have pulsed current peaks in the order of mA this might be a problem: maximum 2 V preamp output at a gain of 0.1 V/pC gives a charge of 20 pC at full energy (12 GeV) within about 10 ns, resulting in about I=Q/t=20 pC/10 ns=2 mA.
  • We need to closer look to this phenomenon

Cabling:

• Claudius presented calculated voltage drops vs. cable cross sections on the LV lines
• There was quite some discussion about:
  • the need of halogen free cables (larger diameter) inside the endcap - much greater selection of cable types available
  • the I2C cabling
  • the grounding scheme of the LV supply: agreed on shielding separated from LV ground