Transcript Gas Electron Multiplier (GEM) - a novel particle detector

A potential cost saver for the
CMS GEM upgrade:
GEM readout with zigzag strips
Marcus Hohlmann
Florida Institute of Technology
CMS GEM Workshop III, April 20, 2012
Motivation
• Cost is one of the biggest current issues for
the CMS GEM upgrade project
• The single-largest budget item in the current
GEM budget estimate is electronics:
~3M out of 6.4M total (TP CMS IN 2012/001)
• Clearly, we should seriously look for ways to
reduce the electronics cost if possible
– One potential real cost saver would be the
significant reduction of readout channels
 Can a zigzag strip readout help with that?
4/20/2012
GEM Workshop III - M. Hohlmann
Previous Work @ BNL
Zigzag strips:
Previous exp. studies show <100 µm resolution with 2 mm strip pitch is possible:
100
y
avalanche
Position Error [µm]
80
60
40
20
0
-203000
3500
4000
4500
5000
5500
6000
6500
7000
-40
-60
-80
-100
x (measured coordinate)
Reconstructed Position [µm]
BNL
Concept:
• Charge sharing among adjacent strips allows quite sensitive position-interpolation in x-direction
• We are sacrificing the measurement of the 2nd coord. (y) to gain precision in the 1st coord. (x)
• CMS GE x/1 detectors are currently intended for 1D-coordinate measurements, so the zigzag
approach is applicable to these detectors
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GEM Workshop III - M. Hohlmann
Zigzag strips vs. straight strips
Pitch [mm]
Typical Resolution
[µm]
Zigzag strips & analog r/o
2.0
80
Straight strips & VFAT
(current design, short end)
0.6
300
Improvement factor
w/ zigzag strips
3.33
3.75
Can reduce # of &
readout channels
(and electronics
cost) by 70% of
current design
Improve resolution
by factor 3-4
A “figure of merit”: 3.33 × 3.75 = 12.5
~ Potential for order of magnitude improvement over current design
 Well worth a try!
4/20/2012
GEM Workshop III - M. Hohlmann
Zigzag r/o PCB (10cm × 10cm)
2 sets of 10cm zigzag strips with different zigzag pitch (along strip)
PCB with
solder finish
24 fine
zigzag
strips
24 coarse
zigzag
strips
Readout Board
for std. CERN
10cm×10cm
Triple-GEM Detector
APV25
Hybrid
(using only 38%
of 128 ch.)
+ SRS
BNL/FIT/Stony Brook Collaboration
0.5 mm
2 mm
Solid ground plane on the back side.
4/20/2012
CAD Design by C. Pancake, Stony Brook
1 mm
LEMO footpads
GEM Workshop III - M. Hohlmann
2 mm
2nd batch: Gold plating finish
Ordered second batch
with gold plating finish
because hot-air
solder leveling
(HASL) finish shows
non-uniform surfaces:
HASL
Much
higher
surface
quality
Au plated
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GEM Workshop III - M. Hohlmann
WHAT ABOUT NOISE?
 First commissioning step addressed noise question:
• Measure pedestals and compare with regular straight strips
• Does the noise increase substantially due to the
increased strip area and capacitance?
4/20/2012
GEM Workshop III - M. Hohlmann
Pedestal Distributions
Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane:
# ev.
per
ch.
straight
strips
ADC channel
APV ch. 63
(example)
pedestal width: r.m.s 3 → 4 cts.
# ev.
per
ch.
zigzag
strips
APV25 Hybrid
(using only 38%
of channels)
+ SRS
ADC channel
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GEM Workshop III - M. Hohlmann
Pedestals for all channels
Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane:
Pedestal width (rms)
[ADC counts]
48 channels connected
to zigzag strips (24+24)
Channels connected
to LEMO footpads (5)
channels not connected
(open APV inputs)
APV channel number
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GEM Workshop III - M. Hohlmann
First pulses with zigzag r/o
GEM stack being
assembled on
zigzag r/o board
Completed Triple-GEM with zigzag
r/o board under gas, HV, and x-rays (Cd109)
Strips ganged together using adapter
board plugged into a
Panasonic connector
Pulses recorded
with ORTEC
preamp and
(slow) lin. amp.
Currently setting
up for cosmics test
with APV + SRS…
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GEM Workshop III - M. Hohlmann
30cm × 30cm zigzag PCB
Plans for next design:
• Design and build a zigzag readout pcb for the 30cm × 30cm self-stretch CMS GEM (on order w/ Rui)
• 128 zigzag strips of 10cm length covering the full 30cm width & read out by a single APV25 hybrid + SRS
• Test also 30cm long strips on same board (given the good noise performance of the 10cm long strips)
Photo-montage
~ 300 mm
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GEM Workshop III - M. Hohlmann
Impact on electronics design
 Potential for removing the need for 2/3 of the electronics of current baseline design:
1
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GEM Workshop III - M. Hohlmann
from Paul
Aspell’s
talk on Thu.
Implications
• Potential for saving 70% of readout channels
and ~50% (?) of electronics cost, could mean
potentially saving 1-1.5 MCHF on the project
• Simplifies also cooling, cabling, power, etc.,
which would lead to additional cost savings
• Total project cost < 5 MCHF possible ?!
• Analog pulse height measurement is
mandatory for charge interpolation, so VFAT3
would not work → need a GdSP design
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GEM Workshop III - M. Hohlmann
Conclusion & Outlook
• Noise increases by only 1.5 ADC counts
(~ 0.1% of range) for zigzag strips compared w/
straight strips. Encouraging!
• Can potentially read out one GE1/1 strip row
with single 128-ch. front-end hybrid while
improving spatial resolution; could lead to
substantial channel number & cost savings.
• Next:
– Measure spatial resolution using tracked cosmics
– Test zigzag prototype in 2012 test beam
– Design, produce & test larger prototype boards
4/20/2012
GEM Workshop III - M. Hohlmann