Minutes of the forward endcap EMC eZuce SRN meeting, 20th of June 2016, 14:00-16:30

Presence:

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

APD preamps:

• Ringing/oscillation problems seem to be solved with latest version (in contast to what was reported on the Collaboration meeting - a faulty test setup caused early bad results...)
  • No ringing even under crtitical conditions: hot/cold operation, parallel LV supply, external excitation (HF vacuum tester)
  • We will replace the two APD-equipped test crystals in the Bonn cosmics test setup (which are currently unable to be read out due to oscillation) with units equipped with this modified preamps
  • Remedy to the ringing problem is a capacitor across the opamp inputs limiting open loop HF gain and therefore increase phase margin in closed feedback loop

VPTTs:

• Markus Kuhlmann is going to finish the VPTT B-field measurements in Bonn
• His first job is an integration of all Bonn B- field data into our detector production database

Subunits:

• As reported on the Collaboration Meeting we are still puzzling over the fact that some APD-equipped crystals show heavily different responses of the two read-out channels
  • Simulations and measurements are going on
  • We can exclude the APDs from being the source of this problem (removed 2-APD read out units do not show different responses to light pulser signals)
  • Candidates are: The glueing, the crystal itself (geometry, run of optical symmetry axes?), the mirror foil (even though it seems to mitigate the problem rather than causing it)
• Glueing turns out to be a seperate problem: We lost many APD-crystal couplings (half of one subunit) and also two VPTT couplings
  • It is always the glue-crystal connection that fails, leaving a clean crystal surface
  • Systematic breakaway tests of different glueing methods are in preparation

Read out electronics:

• Pawel gave a report of the neutron irradiation tests at TSL Uppsala:
  • Two test configurations:
    1. FPGA test under load
    2. Regular read out of ADCs at 3.6 x 10^6 n/cm^2s, corresponding to about 0.4 times the full PANDA luminosity lifetime dose of the ADCs in the forward endcap:
  • All waveforms okay (noise)
  • All baselines okay (no signals used)
  • Repairable problems occur about every 9 h per unit, irrepairable ones (needing reprogramming) every 22 d per unit
  • 700 units: 'repair' necessary every 46 s (taking 300 ms of reinitialization of the FPGA)
  • Effectively no data loss because of 2-APD readout
• For the finalization of the ADC boards Pawel would like to extend the boards somewhat in length and width (5 mm each) in order to to reduce current density
  • Claudius will check if that is possible: In the meantime we know it is not! ​(An extension of the board length will clash with the cooling structures)
• There has been again quite some discussion about the lab ADC readout approaches:
  • Matthias would like to have a 'turnkey system' being able to e.g. sample in front of pulses, allow for triggered readout...
  • It would be "quite a project to dig out the WASA stuff again" for readout, however WASA data concentrators might be available
  • Christoph suggested to rewrite Bonn VHDL code:
    • One channel triggering and pushing all waveforms to the output (UDP packets)
    • Time scale in the order of a week - however, no promises, need to talk to Johannes
    • We decided to follow this approach (there has been some exchange between Johannes an Matthias in the meantime)

Cabling:

• Christoph asked for the confectioning of the HV cables (Draka 5 kV, rad. hard), after some discussion we decided to let both sides be crimped by company and keep some spare length instead of a perfect fit trimming later in the detector hall
• We need to fix the endcap inside LV cabling: the routing is still unclear, single supply of every subunit possible? Bochum will look for suitable LV cables.
• I2C cabling: 4...8 lines from outside needed to enter the full endcap. Bonn will look for suitable I2C cables. Hans suggested to test the suitability of the multi-twisted pair Bedea cables used for barrel signal readout.