Short report on MPPC gain monitoring system

1
Short report onMPPC gain monitoring system

• S. Uozumi
• Jun-27 2008 ScECAL meeting

• At the FNAL BT, having the gain monitoring system
  for all the channel is crucial for
• keep measuring the MPPC gain
• Correct drift of the MPPC gain occurred by
  some reasons.
• Also indispensable for saturation
  correction.
• A few photoelectrons are necessary in each
  channel.
• Electronics inter-calibration
• need to measure gains of electronics in low
  and high gain mode.
• Also necessary for the saturation
  correction.
• Large amount of light (100p.e., at least
  gt10p.e.) is necessary to be distributed.

2
So far, not so good(Ikeda-sans talk on Jun-13)
?acrylic plate ?side emitting fiber 1 ?side
emitting fiber 2 ?optical fiber with
notches
Dark noise level (0.02 p.e.)
3
Revision of the system

• Look over whole system and correct any
  problematic points.
• Optical connections
• status of fiber
• Fixture of fiber
• And so on
• Change LED to very bright one.
• Use CMB to issue LED driving pulses.

4
Some remarks on light distribution

• Connection between different fiber/material
  causes a lot of light loss.
• We should just use clear fibers, rather than
  acrylic bars or side-emitting fibers with clear
  fiber bundles.
• After realizing this, only the choice is clear
  fiber with notches.
• We will adopt it for the FNAL BT.

Acrylic bar
Clear fiber
Almost of lights are lost here
Clear or side-emitting fiber
Clear fiber with v-shape notches
5
Revised bench-test system
CMB
Cable (5cm)
Scintillator-layers (Kuraray fiber
mega-strip used at 2007 DESY BT)
LED
Fiber bundle (20 fibers ganged)
f1mm clear fiber
V-shape notches
6
CMB

• Originally developed for AHCAL calibration system
  by Prague guys.
• Can drive up to 12 LEDs.
• Provide 8-50 ns pulse into LED.
• Currently bench test is ongoing with borrowed
  CMB, but 2 CMBs will be delivered soon from
  Prague.
• Control through CANbus is recently succeeded by
  Daniel.

12 LEDs
CANbus line
Power
TCALIB (timing signal) VCALIB (amplitude signal)
7
LED

• Adopt Nichia NSPW500GS-K1 W-rank white LED
• One of the most efficient LED currently
  available.
• Brightness 31000 - 44000 mcd _at_ IF20mA (x3
  blighter than LED previous used)
• Forward voltage / current 3.2-3.5V / 30mA
  (100mA possible with pulsing mode)
• Emission spectrum more-or-less matches to MPPC
  PDE spectrum.

Blightness (arbitrary unit)
Wavelength l (mm)
PDE of the MPPC
Blightness (arbitrary unit)
Emission angle
8
Clear fiber bundle

• Bundle of 20 clear fibers, made for 2000 HCAL
  beam test _at_ FNAL.
• Diameter of the fiber is 1mm.
• (One concern does it fit to 1 mm gap in
  ScECAL?)
• Fiber length 75cm.
• White disk is attached for fixture purpose.

9
Notches on the clear fiber

• Making many uniform notches is important.
• To achieve that, melting method by heating tool
  would be better than cutting or gliding.
• f0.8mm wire is used as a space to control the
  depth of notches.

LED
Notches

• With the notched fiber, stronger light is emitted
  to opposite side of the notches.

10
Fiber arrangement on the mega-strips

• 3mm-wide slits are made on reflector and black
  sheet.
• (2mm hole will be enough for actual system at
  FNAL)
• Notched fiber is put on the slit (notches come
  upside)
• and fixed by black tape.

Mega-strips (Kuraray fiber readout, used at DESY
BT)
Holes for MPPCs
Notched fiber
To bundle
11
Result of quick test

• CMB DAC count can be set to 0-255 counts.
• (it is proportional to amplitude of the LED
  driving pulse.)
• LED starts flashing around DAC100 counts.
• With DAC120, we saw gt10 photons at most far-side
  strip.
• With higher DAC setting (gt150 DAC count), all the
  strips get too much light which causes ADC
  overflow.
• Plots and numbers will follow soon, but notched
  fiber seems to be distributing large amount of
  lights more than enough!

12
Summary Plans

• Revised system with CMB, new LED and notched
  fibers works well for the MPPC gain monitoring.
• At the first quick test, we saw large amount of
  light with this system.
• Plots, numbers and some more tests will follow
  soon.
• At the same time, we will design the actual
  layout of the system at the FNAL beamline.