Transcript Simulation of the GlueX Experiment

Tagger Electronics
Richard Jones, University of Connecticut
Part 1: tagger focal plane microscope
Part 2: tagger fixed array
Part 3: trigger and digitization
GlueX Electronics Meeting Apr. 6-7, 2006, Bloomington
Tagger focal plane
 broad-band focal plane
hodoscope



144 readout channels
short scint. rods
max rate/chan: 2x106 (107)
photon beam exits from
tagger inside vacuum,
continues 70 m down
to collimator cave
and Hall D
 focal plane microscope



120 readout channels
600 scint. fibers
max rate/chan: 2x105 (106)
• hodoscope exit window is 1 mm Al
• other walls of vacuum chamber are 1 cm Al
• exposed side of electron exit channel is 5 mm Al
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Microscope scintillating fiber design
 Design
parameters
 square scintillating fibers
 size 2 mm x 2 mm x 20 mm
 clear light guide readout
 aligned along electron direction
for reduced background sensitivity
SiPM sensors
clear light fibers
scintillating fibers
focal plane
electron trajectory
 readout with silicon photomultipliers
(SiPM devices)
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Why 2D segmentation?
y
9 GeV
qy
3qy
3 GeV
(P kick from crystal is negligible)
collimator

This photon cannot get through the collimator but its electron still
reaches the focal plane and produces a count there.

By reducing the acceptance of the tagging counters to a region
| qy | < qhalf-collimator
part of the tagging efficiency lost through collimation is recovered.
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Silicon photomultiplier fiber readout
 Excellent characteristics for this application:
Fast timing (x2 faster than PMT’s)
Dynamic range factor 1000-10000
Gain similar to phototube (106)
Requires no HV (only ~50V bias)
QE similar to PMT (higher in green, lower in blue)
 Data reported by
l
Device
e
SiPM
PMT
SiPM
PMT
0.3
1.0
0.3
1.0
QE
h
G. Lolos et.al.
550 nm
437 nm
60% 20%
5%
5%
45% 15%
25% 25%
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Microscope requirements: channel count
1. channel width from energy resolution:
9 MeV
2. channel width from rate limitations:
2 MHz
= 4 MeV
500 MHz/GeV
3. additional margins:
30% margins
2 MHz is the rate seen by the
central fiber for the case of
transverse segmentation
100 energy channels
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Silicon photomultiplier fiber readout
 Expected light yield for axial electrons:


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total path length in scintillator: 2 cm
scintillation light emitted: 104 photons / MeV
fiber capture fraction: 5%
quantum efficiency: 15%
SiPM coupling fraction: 20%
60 p.e.
 One complete electronics chain per energy channel
 Individual SiPM bias voltage setting under computer control
 Conventional tagging is remotely selectable by enabling all rows
 Tagger Review Panel (1/2006):
A few channels should have readout on all 5 fibers
to enable monitoring of the stability of alignment.
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Microscope electronics
 SiPM “bases”

provides bias voltage regulation:

regulation range: 48 ± 8 V
regulation stability: 0.1 V

regulation control: 0.1 V steps

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reasonable packing density: 600 channels on 20x103 cm2
 Programmable constant fraction discriminators: 120 channels
 High resolution tdc (F1TDC): 120 channels
 Pulse height needed: FADC is a good choice: 120 channels



essential for setup
useful for monitoring performance
rates alone give incomplete information
 Scalers counting on all channels: 120 channels
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Fixed array electronics
 Conventional 1” phototubes, bases
 High voltage for phototubes: 144 channels
 Timing needed: High resolution tdc (F1TDC): 144 channels

for measuring coherent bremsstrahlung spectrum

time is compared with pair spectrometer trigger

at low intensities (10 ) can run concurrently with experiment

at high intensities (108) only for special low-intensity runs
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 Pulse height needed: FADC may not be a good choice: 144 channels

essential for setup

at high intensities, monitor spectrum in integrating mode
 Scalers counting on all channels: 144 channels
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Channel count updates

discussion…
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006
Tagger trigger electronics
 TaggerOR
 fast logical OR of 120 channels from the microscope
 sent over fiber to GlueX trigger electronics
 Digitization of tagger signals
 probably located in the tagger area
 requires delivery of the GlueX clock and trigger to
tagger area
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Richard Jones, GlueX Electronics Meeting, Bloomington, April 6-7, 2006