GEM DETECTORS
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Transcript of GEM DETECTORS
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GEM DETECTORSGas Electron Multiplier
Bat-El Pinchasik, Technion Israel
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GEM detectors main elementGEM foil
10 cm
Millions of
holes! Kapton (polyimide) copper-clad on both
sides
Terminals
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CATHODE
ANODEINDUCTION REGION
GEM
GAS ATMOSPHERE CO2+ Argon
DRIFT REGION
segmentation
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Field lines
Drift field
Induction field
GEM foil
Electrons follow
the field lines
In the holes: high
density of field lines
Electrons gain energy!
500 volts50μm
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Simulation:Ions
Gain of the detector
Electron-Ion pair
GEM
Drift field
Induction field
CATHODE
ANODE
Electrons are
shared between bottom
GEM and anode
Top
Bottom
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AdvantagesDetector Area
covered by a
detector
Cost(per area)
Rate capabili
ty
Aging process
GEM detecto
r
$$ Low aging
Wire chambe
r
$ Gain loss and
discharges increase
Silicon detecto
rs
Noise and leakage current increase
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STANDARD GEM
CONICAL GEM
72µm
40µm
• Easy to produce• larger detectors• low cost per area
• First invented in 1998• Double conical geometry• Used already in several experiments
42.5µm
98.9µm
copper
kapton
copper
Recent
development!
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Glance from above
Conical GEM- Top Conical GEM-Bottom
Standard GEM
Internal & External diameter
Larger diameter
smaller diameter
140 µm
140 µm
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See the difference
10 X 10 cm
Large conical GEM
foil
Does a conical GEM have the same characteristics?
60 cm
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CATHODE
ANODEInduction
field
Voltage over the GEM
GAS ATMOSPHERE CO2+ Argon
Drift field
Anode current
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Drift field scan
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
0.2
0.4
0.6
0.8
1conycal
standard
I anode (nor-malized)I anode (nor-malized)I anode (nor-malized)
conical
E drift (Volts/cm)
GEM voltage: 500 voltsE induction: 3 (kv/cm)
Recombination
plateau
Electrons end up in Top GEM
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Gain vs. GEM voltage
300 350 400 450 500 550 600 6505
50
500
standard
Gem voltage (volt)
Gain of the
detector
Log scal
e
E induction: 3kv/cmE drift: 2 kv/cm
Gain Integration over distance
Townsend coefficient
Field & gas
properties
α
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Induction scan
0 1000 2000 3000 4000 5000 6000 70000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1 conicalstandard
I anode (normalized)
E induction (volt/cm)
Electrons distributio
n
Increasing induction field
More electrons get to the anode
Higher signal
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ConclusionsResults
• Conical GEM has similar performance as standard GEM
Advantages•Low cost•Larger area•Easy to fabricate
Conclusion• Conical GEM is an
attractive candidate to future LHC upgrades
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Current applications
COMPASS
TOTEM
LHCB
And the future?
LHCB muon