GEM DETECTORSGas Electron Multiplier

Bat-El Pinchasik, Technion Israel

GEM detectors main elementGEM foil

10 cm

Millions of

holes! Kapton (polyimide) copper-clad on both

sides

Terminals

CATHODE

ANODEINDUCTION REGION

GEM

GAS ATMOSPHERE CO2+ Argon

DRIFT REGION

segmentation

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

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

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

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!

Glance from above

Conical GEM- Top Conical GEM-Bottom

Standard GEM

Internal & External diameter

Larger diameter

smaller diameter

140 µm

140 µm

See the difference

10 X 10 cm

Large conical GEM

foil

Does a conical GEM have the same characteristics?

60 cm

CATHODE

ANODEInduction

field

Voltage over the GEM

GAS ATMOSPHERE CO2+ Argon

Drift field

Anode current

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

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

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

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

Current applications

COMPASS

TOTEM

LHCB

And the future?

LHCB muon