Forward Tracker Scintillator Trigger (FTST)

The FTD upgrade requires the removal of the forward MWPC's which will destroy the current forward ray trigger. Although this will, to some degree, be replaced by the new CIP z-vertex trigger, the very forward region, theta < 12 degrees, will not be covered.
The intention is to add a new trigger system, the FTST, based on scintillation counters which will cover upto a theta of approx 17.0 + degrees and:

• will provide an accurate determination of the proton satellite bunch crossings, increasing the accuracy of the H1 luminosity measurement.
• match the liquid argon calorimeter "big-tower" geometry and, in coincidence with the calorimeter, improve the triggering on forward going tracks.
• will provide a cosmic ray trigger for testing/calibration of the FTD.
• could provide a useful monitor for beam tuning.

The proposed system consists of two separate planes of scintillation detectors :-

• the FTST-1, situated on the -z side of the FTD.
  Segmentation in phi : 8
  Segmentation in r : 2
  Outer radius : approx. 45 cm
  Inner radius : approx. 12 cm
  
• the FTST-2, situated on the +z side of the FTD
  Segmentation in phi : 16
  Segmentation in r : 2
  Outer radius : approx. 85 cm
  Inner radius : approx. 23 cm
  
• The planes would be rotated by 360/32 degrees relative to each other to give a 1:3 trigger correspondence.
• Aim for time resolution of the order of 1 nS.
• In addition we would keep the present FIT detector.

3.1 FTST-1

• space NOT an issue
• could use the present FITS design and SPACAL type PM tubes
• need to check the design viability for 10 mm thick scintillator (which is available now)

• space IS an issue
• detector is in region of GO magnet support
• as yet have no detailed design of this region
• need to know design constraints
• do we integrate the within magnet support structure?
• will most likely need small photodetector devices
• several detector designs are under review:
  1. Scintillator tile + WLS Bar (10 X 10 mm square section attached to one edge of scintillator) + HPD + P/A
  2. Scintillator tile + WLS Fibres (with fibres laid along edge of tile) + HPD + P/A
  3. Scintillator tile + WLS Fibres (with fibres laid in machined grooves on surface of tile's larger face) + HPD + P/A

3.3 R & D

R&D required in the following areas :

• detector optical simulation and design
• detector mechanical/electrical design optimisation
  (depends on final physical layout - urgently needs design input)
• scintillator tile prototyping and testing
• electronics (particularly HPD + P/A + Cable chain optimisation)

4. System Specifications

4.1 Scintillator

1. Bicron Type BC-412 (Available)
   Rise Time 1.0 ns
   Decay Time 3.3 ns
   Pulse Width,FWHM 4.2 ns
   Light Attenuation 210 cm
   Wavelength of 434 nm
   maximum emission
   Density 1.032 g/cc
   Ref. Index 1.58
2. Bicron Type BC-412 (Available)
   Rise Time 1.0 ns
   Decay Time 3.3 ns
   Pulse Width,FWHM 4.2 ns
   Light Attenuation 210 cm
   Wavelength of 434 nm
   maximum emission
   Density 1.032 g/cc
   Ref. Index 1.58

• Bicron Type BC482A (Available) *
  Decay Time 12 ns
  Light Attenuation 400 cm
  Absorption Peak 420 nm
  Wavelength of 444 nm
  maximum emission
  Density 1.03 g/cc
  Ref. Index 1.59
  

4.3 WLS Fibres

• under investigation

• specifications as per SPACAL tubes

• Maximum Ratings
  Supply Voltage 8000 Vdc
  Diode Reverse Voltage 70 V
  Ambient Temperature -40 to +50 degrees C
  
• Characteristics (at 25 degrees C)
  Cathode Sensitivity
  Luminous(2856K) 100 Min 130 Typ microamp/lm
  Radiant at 420 nm 51 Typ mA/W
  Gain 1000 (linear with V)
  @ photocathode voltage : -6 kV,diode reverse voltage : 30 V
  (Gain of the Si-Avalanche diode target type is typically 4 X 10e4
  @ photocathode voltage : -8 kV,diode reverse voltage : 145 V)
  Time Response 2.4 ns
  Diode(Target)
  Leakage Current 3 nA
  Capacitance 15 pF

• RAL designed low noise charge amplifier (~1000 electrons RMS noise for 30 pF input C)
• size of pcb 58.0 X 19.0 X 1.6 mm (it is possible that this could be reduced to approx 30.0 X 19.0 X 1.6 mm)
• HPD and P/A as close as possible (minimise C), remote HPD to P/A means typically 150 mm.
• careful design of detector/pre-amp/shielding/HV/Bias/LV needed
• investigate use of transformer coupling of P/A to O/P cables?