Ladungsträgertransportim …ilctpc/Publications/dpg2003_k...Ladungsträgertransportim GasElectronMultiplier(GEM) ... cathode readout plane (anode) ... Cathode GEM Readout PCB

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


100k

30k

10k

3k

1k

300

100


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


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?


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


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)

100k

30k

10k

3k

1k

300

100

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]


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


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]


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


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]


Consequences for the TPC application?1st GEM in magnetic fields...

0 20k 40k 60k 80k 100k0

50

100

150

200

250

300

350

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


+ 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


+ 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

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Ladungsträgertransportim …ilctpc/Publications/dpg2003_k...Ladungsträgertransportim GasElectronMultiplier(GEM) ... cathode readout plane (anode) ... Cathode GEM Readout PCB