Post on 10-May-2018
Ladungstr gertransport im Gas Electron Multiplier (GEM)äKonsequenzen f r die Anwendung in Zeitprojektionskammernü
Frühjahrstagungen derDeutschen Physikalischen Gesellschaft
Sitzung T 407 - Spurkammern
Aachen12. März 2003
*S. Kappler1,2 1 1 2 2, J. Kaminski , T. Müller , L. Ropelewski , F.SauliB. Ketzer , B. Ledermann ,2 1
Institut ExperimentelleKernphysik, rlsruhe (Deutschland)f Universit t Ka1 ä2 CERN, EP Division,Genf(Schweiz)
ür
The Gas Electron Multiplieras Preamplification S tage
The GEM foil
+ Kapton foil of 50 m thickness,two-side copper-clad (5 m each)
+ Perforated with a high density of holes(etched in a photolithographic process)
+ Typically“Standard GEM”
µµ
µ µ µp=140 m, D=70 m, d=60 m
p
Delectron microscope photograph
50 mµ
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
The Multi-GEM DetectorGeneral Design
conversion&drift gap
+ Parallel plate detector withone or more GEMs inserted
Principle:
transfergap
inductiongap
+ Adaptable eff. gain(# of GEMs, GEM-voltage)
+ Large-area detectors at low cost
+ Separation of gas amplificationand readout stage allows
Features:
high flexibility in the readoutdesign
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
100k
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10k
3k
1k
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100
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
The GEM Technology in TPCsMotivation
Intrinsic GEM properties:
+ High spatial resolution as well as fast andnarrow signals and
+ Configuration of the el. fielda) intrinsically
b) causes
+ Highest flexibility in thereadout pad design
+ Device capable ofhigh rates
increasegranularitymulti-track resolution
suppressesthe ion feedback
almostno effectsE Bx
beampipe
E
driftcathode
readoutplane
(anode)
+ -
+ -
+ -
+ -
+ -
+ -+ -+ -+ -
+ -+ -
+ -
+ -
+ -
+ -+ -+ -+ -
+ -
+ -
+ -
+ -
+ -
+ -
+ -+ -+ -+ -
+ -+ -
+ -
outer fieldcage
innerfieldcage
electrondriftvelocity u
+
++
+
+
++
Precise gain calibration, avoiding orcontrolling charging-up effects
Ensuring no losses of primary electronsbefore multiplication, investigation of thecharge carrier transfer in the GEM
b) energy resolution
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
The GEM Technology in TPCsPoints to clarify
Possible Problems:
Aging tests with prototypes
+ Measurement of the electron andion transmission at low GEM voltages( region) for TPC-like fields
+ Extrapolation to the region of gasamplification & magnetic fields
G=1
This presentation:
+ Aging in TPC specific gases?
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
Charge carrier transfer in the GEMMeasurement Method
10mm[~150V/cm]
2.5 mm [2.5kV/cm]
DriftCathode
GEM
ReadoutPCB
Readout-Current
Drift-Current
HighRateX-Rays
GEM-Currents
Single-GEM Detector:
t = κε κ:ε:
collectionefficiencyextraction efficiency
readout electrode currentnormalization current
I :I :
RO
N
=IRO
IN
+ High flux of 6.4keV X-rays+ Measurement of all electrode currents+ Determination of the transmission
+ Sideways (!) irradiation of the drift volume
+ I
(Noprimaryionization in theinductiongap)
(voltages ofoppositepolarity)dentical method for ion transmission measurement
0 25 50 75 100 125 150 175 200 225-100
-50
0
50
100
150
200
readoutanodeGEM, bottomGEM, topsum
UGEM [V]
0.0
0.5
1.0
1.5
2.0
IN
StandardGEM, E = 150V/cm,E = 2.5kV/cm,inAr-CO 70:30D I 2
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
Charge carrier transfer: Different gasesRegion of low gas gain
0 25 50 75 100 125 150 175 200 225 2500.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
StandardGEM5.9keVX-rays,sideways
ED =150V/cmEI =2.5kV/cm
>99% C O270:30Ar-CO290:10Ar-CO2>99%ArP10
UG EM [V]0 25 50 75 100 125 150 175 200 225 250
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
StandardGEM5.9keVX-rays,sideways
ED =150V/cmEI =2.5kV/cm
>99%CO270:30Ar-CO
290:10Ar-CO2P10
UGEM [V]
150V/cm2.5kV/cm = 0.06
+ Similar ion transmission for different gases
+ Ion transmission is below but close to theratio of external fields
e Transmission-Ion Transmission
+ electron transmission in CO
+ Decreasing electron transmission withincreasing transverse diffusion
Full 2
(s. nextslide)
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Electric field in a Standard GEMwith MAXWELL 3D & GARFIELD:
MAGBOLTZ data for Ar-CO & P10:2
E = 150V/cm, E =2.5kV/cm, U =100VD I GEM
100 1k 10k 100k0
200
400
600
800
CO2Ar-CO2 (70:30)Ar-CO2 (90:10)ArgonP10,Ar-CH4 (90:10)
E [V/cm]
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
Charge carrier transfer: Diffusion in the GEM holeDifferent gases
Transverse diffusion can get sufficiently large to cause electronlosses to w alls or electrodes inside or close to the GEM holes!
Charge carrier transfer: Different geometryRegion of low gas gain
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
Again full e -transmission when increasing pitch hole diameter!less gain...
- andBut:
p=140 mD=70 md=60 m
µµµ
StandardGEM
p=380 mD=140 md=120 m
µµµ
DoubleSize GEM
Optical transparency is kept identicali.o. not toincrease theiontransmission
Measurement Results:Variation of pitch & hole size:
0 25 50 75 100 125 150 175 2000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
//
t ion = 0.043 @ 100Vt ion = 0.032 @ 100V
//
5.9keVX-rays,sidewaysED =150V/cmEI =2.5kV/cmAr-CO2 90:10
Standard GEMDoubleSizeGEM
UGEM [V]
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
Simulations with / without Diffusion?Limitations of the predictive power...
Caution:
+ According to the author of GARFIELD (R. Veenhof),the MC drift routines in the current version ofGARFIELD are not suitable for strongly convergentor divergent fields (like they occur in the GEM andother MPGDs).
Can diffusion be neglected?
+ In cases, where the transversediffusion inside theGEM holes is not significantly smaller than the holeradius, .
+ In these cases, drift line plots using themethod (like the one on the right) have
and a Monte-Carlo (MC)study has tobeperformed.
diffusion should not be neglected
no predictivepower
Runge-Kutta
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
The Standard GEM in amplification mode at TPC-likedrift fields should not lose primaries!
Consequences for the TPC application?1st GEM in amplificationmode...
Extrapolation from thecase to the normalamplification mode :
U =100VGEM
+ In P10 at voltages thetransverse diffusion inside the holedrops to per
+ This is comparable to what wefound for pure CO at
U >300V
U =100V
GEM
GEM
~150 m 1cmµ
2
[red][blue]
20.0k 40.0k 60.0k 80.0k 100.0k0
200
400
CO2P10, Ar-CH4 (90:10)
E [V/cm]
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
Consequences for the TPC application?1st GEM in magnetic fields...
0 20k 40k 60k 80k 100k0
50
100
150
200
250
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400
450
500
B = 0long. transv.
B = 2.5T,B||Elong. transv.
B = 5.0T,B||Elong. transv.
Electric field E [V/cm]
U =100VGEM case
+ In P10 the presence of a 5Tmagnetic field drops the transversediffusion inside the hole bydown to per
15%~250 m 1cmµ
[red]:
Normal amplification mode :
+ In P10 at voltages thetransverse diffusion inside the holeis not strongly affected
U >300VGEM
[blue]
The Double Size GEM at TPC-like drift fieldsshould not lose primaries!
Conclusions
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
+ Apart from the configuration of the electric fields, which givesthe essential condition for charge carrier transfer in the GEM,
+ In simulations, where the transverse diffusion inside the GEM holes is notsignificantly smaller than the hole radius,
diffusion processes are mainly responsible for losses ofprimary electrons.
diffusion should not be neglected.
+ The GEM technology is capable tobefore gas amplification.
+ Depending on the operation voltage of the (and thus the effective gain),must be .
+ For drift fields in P10 [Ar-CH (90:10)] we found:a) In ( ), the should
not show losses of primary electrons before gas amplification.b)At , a will be necessary.
preserve almost all primary electrons
first GEMdiameter and pitch of the GEM holes optimized
TPC-likenormal amplification mode
low gains
4
U >300VGEM Standard GEM
Double Size GEM
Zusammenfassung
SteffenKapplerIEKP,KarlsruheUniversity(Germany) CERN,Geneva(Switzerland)
+ Neben der Konfiguration des elektrischen Feldes, welche denRahmen für den Ladungsträgertransport durch dieGEM-Folieschafft, sind hauptsächlich
verantwortlich.für Verluste primärer Elektronen
Diffusionsprozesse
+ Gegebenenfalls müssen dazu, je nach angestrebter Betriebsspannung derGEM-Folie, angepasst werden.
erstenDurchmesser und Abstand der GEM-Löcher
+ Bei Simulationen, in welchen die transversale Diffusion in den GEM-Löchernnicht signifikant kleiner als der Lochradius ist, dürfen Diffusionseffekte nichtvernachlässigt werden.
+ Generell können mit der GEM-Technologie diegehalten werden.
Verluste primärer Elektronenvor dem Gasverstärkungsprozess im Bereich 10-2
+ Für und [Ar-CH (90:10)] stellte sich heraus, dassa) im ( ) eine
Verluste primärer Elektronen vor der Gasverstärkung aufweisen sollteb) bei hierzu eine notwendig
würde.
TPC-artige Driftfelder P10normalen Gasverstärkungsmodus
keinegeringen Gasverstärkungen
4
U >300VGEM Standard GEM
Double Size GEM