Minutes of the forward endcap EMC SeeVogh meeting, 14th March 2016, 14:00-15:00

Presence:

• Basel: Werner
• Bochum: Claudius, Fritz-Herbert, Tobias, Tom
• Bonn: Christoph, Matthias
• Giessen: excused
• Groningen: Myroslav
• Stockholm: Karoly, Markus
• Uppsala: Pawel
• GSI: -

Summary of Discussions at Bochum Collaboration Meeting:

• There is no solution to the question of how to properly wrap the crystals with DF 2000 MA reflective foil:
  • Talking to the backward endcap people revealed no progress by using double laser cut edges to account for the chamfered crystal edges
  • The foil remains improperly surrounding the crystal as with the old shape design
• We need to start series production of subunits
  • Start with VPTT subunits:
    • All VPTTs are available, gain measuerd, and most of them also B-field measured
    • Remaining B-field measurements will start in two weeks and last about 2-3 months
    • However, B-field dependence showed up to very consistent from tube to tube, so grouping of VPTTs to crystals can start already
    • Glueing tests in the climate chamber with new cleaning procedure (special Dow Corning fluid) fully satisfying
    • Crystal foil covering problem much less pronounced in VPTT 'final prototype' subunit
    • So we will start to produce VPTT subunits 'now' (need cables from Bonn...)
  • Still open questions with APD subunits:
    • What really causes the huge response differences between two APDs on some of the crystals? (Geometry, cover foil, improper biasing?)
    • What preamp gain will we need/be able to realize for stable operation?
• We discussed to start work on open APD subunit questions parallel in Bonn and Bochum:
  • Readout of a crystal with two (fully AC/DC screened) APDs (Bochum), readout of a crystal with 16-anode PMT (Bonn), starting with a 'naked' crystal, then wrap in mirror foil etc.
  • What kind of light source should be used? Any coupling of light from outside the crystals results in very limited angular distribution and may hardly represent the situation of scintillation light (remember quite different results from beam and light pulser runs in the past)
  • We therefore like to test whether we can 'see' DC signals with the APDs (current) as response to scintillations resulting from high rate radioactive sources
• During the EMC session the question arose again if we can realize (from the space point of view) a single channel HV trimming for each APD as the barrel EMC group is planning to do
  • This would make life a lot easier as the need for precise pairing of APD gains and gain gradients (T, U) would become less stringent
  • Christoph got in touch with Hans-Georg who already tested such HV trimming shunt regulator circuit and is thinking about an integration of such circuits to the (somewhat extended) backplate PCBs (aka 'Schmidt boards')
  • In the forward endcap we would need to allocate some additional space for cabling (I2C bus)
  • There will be a bachelor student available from April on to work on this (Bonn)

Basel preamps:

• We would like to invite Werner to visit Bochum again for one or two days in order to go on with work on the APD preamp/connection started during the collaboration meeting
• Werner agreed but would like to see all improvements he suggested to be carried out and checked before
• Pawel asked for the possibility of design changes to the preamps:
  • Shaping to shorter signals (reduced power dissipation)
  • Use of different opamp type?
• While one may think of modifications to the APD preamps (some still need to be done anyway: oscillation, ringing), all VPTT preamps are produced already
• Werner advised to not use the APD-lab 'gold connector' extension pins for sensitive measurements as they unneccessarily extend the wiring length between detector and preamp!

Readout electronics:

• Due to an accidental damage to one ADC board we are quite short of ADCs
• We decided to ship the one ADC board available at Uppsala to Bochum first in order to perform 'full readout chain' measurements as long as we (Bochum) have the TRB borrowed form Mainz (until end of April)
• The ADC board will then be shipped to Stockholm as they are not prepared to use it right now anyway
• Malte will/has contact(ed) Peter Schakel and arrange a visit to Bochum in order to setup the full readout chain (maybe assisted by Mysroslav via phone)
• Markus reported from their work with a Virtex ADC board plus TRB 3, they got out some data, still testing to be done