Fred Hartjes 1 2 nd RD51collaboration meeting, Paris, October13 - 15, 2008 MPGD ageing Fred Hartjes...

Fred Hartjes 1

2nd RD51collaboration meeting, Paris, October13 - 15, 2008

MPGD ageing

2nd RD51 collaboration meetingParis, October 13 - 15, 2008

Fred Hartjes 2


What is ageing of a gaseous detector?

Loss of avalanche gain Rapid or slower

Broadening amplitude spectrum => More variation in gas gain

Increased sparking tendency => Damage on electrodes

Secondary emission from cathode

Increased dark current

After pulsing

Self-sustained discharge

J. Va'vra, NIM A387(1997)183J. Va'vra, NIM A387(1997)183

F.Hartjes, MSGC damage

Fred Hartjes 3


Loss of gain in gaseous detectors Figure of merit: accumulated charge on the anode surface

Kadyk (I. Juricic, J.A. Kadyk, Proceedings Workshop on Radiation Damage to Wire Chambers, Berkeley 1986, p. 141)

where Q is the accumulated charge per cm anode (wires or strips) or cm2 (MPGD, PPC, ….) G is the gas gain D is the dose (particles per cm resp cm2

ne is the primary ionisation per hit

Define the ageing rate R (%/C/cm) or (%/C/cm2) as

where A is the average magnitude of the charge signal

Example for wire chambers

R = 1 %/ C/cm => excellent R = 200 %/C/cm => bad

enDGQ **

A

A

QR

*

1

Fred Hartjes 4


Competition: ageing of silicon sensors

Figure of merit: neq dose Damage from applied radiation converted into damage from radiation caused by 1 MeV

neutrons => easy evaluation of radiation hardness Often using neutrons from nuclear plant for ageing characterisation

Nature of silicon sensor damage Increase of depletion voltage

Presently “solved” using oxygenated silicon (RD50 activities)

Decrease resistivity Rock hard phenomenon => go to low temperature (-30 C)

Decrease of the mean free path Rock hard phenomenon

=> practical limit for regular oxygenated silicon sensors

3*1015 neq / cm2

(Not speaking about 3D silicon, diamond, …..)

Fred Hartjes 5


Do gaseous detectors have better ageing prospects

than silicon? Not possible to give an absolute comparison

Too many different sensor properties involved Response to uncharged particles (neutrons) Gas gain geometry

Required ageing performance of MPGDs to be competitive with silicon Gas gain by Micromegas or GEM Assume thin drift space MIP irradiation ne = 30/hit

Gas gain = 2000

3*1015 neq/cm2 ≈ 6*1015 MIPs/cm2 => accumulated charge 29 C/cm2 (GEM, Micromegas)

=> 0.2 C/cm (wire chambers, integrated anode surface)

Conclusion: Gaseous pixel detectors can be more radhard than silicon, but we have to be careful

Fred Hartjes 6


Obtained so far for GEM and Micromegas

Gossip 23Nov 28Ar/iC4H10 70/30Particle flux: 1.6 GHz

Gossip ageing using mips from 90Sr source

Time (days)0 5 10 15 20 25

I ce

ntr

e (

nA

)

0

50

100

150

200

G = 1000 G = 1000

Fluence (mips/cm2)

0 1e+15 2e+15 3e+15

C/cm20 2 4 6 8 10 12

switch fromVgrid = -635 to -640 V

MicromegasMicromegas(Nikhef measurement)(Nikhef measurement)

GEMGEM

M. Alfonsi et al, M. Alfonsi et al, Nucl. Instr. and Meth. A518(2004)106Nucl. Instr. and Meth. A518(2004)106

Fred Hartjes 7


Micromegas ageing

7

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

13/04/07 14/04/07 15/04/07 16/04/07 17/04/07 18/04/07 19/04/07 20/04/07 21/04/07 22/04/07 23/04/07 24/04/07

Nor

mal

ized

uni

t

Time (d)

- Mesh current- Mesh current

Ar/CF4/Iso (95:3:2)16,1 C / cm² ~ 20 LHC yearsDavid Attié, MPGD workshop CERN Sept. 2007David Attié, MPGD workshop CERN Sept. 2007

Fred Hartjes 8


Loss of gain: rapid Rapid ageing is generally caused by

the formation of a polymer on the

anode surface

Catalysed by pollutants

mC/cm range for wires/strips

May be removed by etchants

CF4, O2, H2O

Possible polymer reaction

C2H4 → 2CH2:

CH2: extremely reactive radical, can

easily build polymer chains

Studied by plasma physicists


Time (days)0.0 0.1 0.2 0.3 0.4 0.5 0.6

I cen

tre (

nA

)

0

50

100

150

200

G = 1000G = 1000

Fluence (mips/cm2)

0 2e+13 4e+13 6e+13 8e+13

Charge (C/cm2)0.00 0.05 0.10 0.15 0.20 0.25

Ar/iC4H10

DME/CO2

Preliminary

Gossip 25June 4, 2008DME/CO2 59/41Particle flux: 2.206 GHz

The most reactive fragment The most reactive fragment is assumed to be CHis assumed to be CH22::

Nikhef measurementNikhef measurement

0.3 C/cm2

Fred Hartjes 9


Polymerization in a plasma

Extensively studied by plasma physicists

But I find no explanation for the rapid ageing catalyzed by minor traces of pollutants

H. Yasuda, Desy Ageing workshop 2001H. Yasuda, Desy Ageing workshop 2001

Fred Hartjes 10


Example of rapid ageing: MSGC

Gas: DME/CO2 60/40 Low dose applied (0.5 mC/cm)

Result: anode strip covered by a thick transparent wax-like layer (Scratch made on purpose for better

visibility)

=> big decrease in gas gain

Irra

diat

ed (

0.5

mC

/cm

)

Non

-irr

adia

ted

100

µm

Fred Hartjes 11


Preventing/ curing rapid ageing

Very clean gas system Do not use outgassing materials in the chamber

Use CF4

(controversial)

Use DME (controversial)

Add some water (who knows) Few percent O2

May help in certain occasions

Is this all sufficient?

NO

Fred Hartjes 12


CF4, a controversial gas CF4 + CH4 induces polymerisation;

while CF4 + CO2 removes polymerisation

In general CF4 + oxygen containing mols helps

Polymerisation also observed in low pressure plasma discharge of pure CF4

Winfred and Eva Stoffels, TU Eindhoven, Netherlands (http://www.phys.tue.nl/EPG/epghome/papers/1999/lunter1.ppt)

High primary ionisation (51 clusters/cm, only DME and isobutane are better)

Non-flammable, Fast drifting, Low diffusion

but Aggressive with water

Formation of HF Used in silicon photolithography as plasma etchant => May damage chamber materials, electrodes

May also clean electrodes (with water)

Highly electronegative at fields (>4 kV/cm) (unpublished private experience)

=> “eats” part of the primary ionisation in the transition between drift area and amplification area

Ar/CF4/CO2Ar/CF4/CH4

A. Romaniuk et al, A. Romaniuk et al, Nucl. Instr. and Meth. A515(2003)166Nucl. Instr. and Meth. A515(2003)166

Mar Capeans,Mar Capeans,MPGD workshop CERN Sept. 2007MPGD workshop CERN Sept. 2007

Fred Hartjes 13


CF4 + water

Water (0.14%) is needed to avoid ageing Hermes wire chambers

S. Belostotski et al, Nucl. Instr. and Meth. A591 (2008) 353S. Belostotski et al, Nucl. Instr. and Meth. A591 (2008) 353

Fred Hartjes 14


DME, another controversial gas

Best quencher of all commonly used HC Good absorber for 6.5 eV photons good cure for rapid after-pulsing

Excellent ageing properties R = 0.7 +/- 0.3 %/C/cmV. Blinov, Desy ageing workshop 2001V. Blinov, Desy ageing workshop 2001

Very low diffusion High primary ionization

but

Highly flammable Chemically aggressive

Attaches most plastics Even Kapton

Not delivered in high purity grade

Va’vra, Desy ageing workshop 2001

M. Capeans, Desy ageing workshop 2001

Fred Hartjes 15


Water Mostly not too good With CF4 is may cure ageing But often makes ageing worse May stabilize HV behaviour by

adding conductivity to insulating surfaces

Often hard to bring down to the ppM level high diffusion through most plastics

M. Hildebrandt, Desy Ageing workshop 2001 M. Hildebrandt, Desy Ageing workshop 2001

o May also enhance dischargeso Much more discharges with 100 ppM than with 10 ppM

Discharge probability

Fred Hartjes 16


Inorganic deposits

Inorganic deposits often consist of silicon or carbon

whiskers

Normally in the higher dose range (100 mC/cm or

more)

Induce drop in gain

Broaden charge signal spectrum

Often induce sparking or dark current

Often originate from very low concentration pollutants

ppb level

Bubbler with silicon oil downstream

A few silicon containing gases exist: SiH4, CSiH6, C2SiH8

The mechanism of creation is mostly unknown

Not easy or impossible to cure

M. Binkley et al, Nucl. Instr. and Meth.A515(2003)53M. Binkley et al, Nucl. Instr. and Meth.A515(2003)53

Fred Hartjes 17


Dark current Secondary emission from cathode

Malter effect

L.Malter, Phys. Rev. 50 (1936) Electrons drawn from a metal surface by a high

field from ions attached to an insulating layer on the surface

Oily residues Polymer from ageing process Skin of conductive glue

Dark currents may also be induced by Sharp points on cathode or anode Small cathode surface

Basically adds up to anode ageing

Avoiding Malter by applying large equally charged cathode surfaces circular drift tube good single cathode wire in wire chambers bad

++++++++

--------

cath

ode

Insulating film

Malter effect

Fred Hartjes 18


Material selection Choose low-out gassing materials

from Database from CERN

gasgroup/RD10 (piping + elastomers)

http://detector-gas-systems.web.cern.ch/detector-gas-systems/HomePage/homePage.htm Nasa database (very extensive)

http://outgassing.nasa.gov/

Why difference between Araldite 103 and 106??

In UseNONOTRABOND 2115ATLAS/TRT

In UseNONOARALDITE AW103(Hardener HY 991)

CERN/GDD

ATLAS/TRT

In UseNONOECCOBOND 285HERA-B/ITR

CERN/GDD

HERA-B/OTR

CERN/GDD

Source

Out ofproduction

In Use

Longcuring time

Note

NONOHEXCEL EPO 93L

NONOSTYCAST 1266(A+Catalyst 9)

NO

Effect inG.D.

NOSTYCAST 1266(A+B)

OutgasProduct

Low Outgassing room-T epoxies

BADYESARALDITE AW 106

(Hardener HV 935 U)

CERN/GDD

ATLAS/TRT

BAD-YESEPOTEK E905CERN/GDD

BAD-YESNORLAND NEA 123(UV)

CERN/GDD

BAD-YESTECHNICOLL 8862

+ (Hardener 8263)CERN/GDD

BAD-YESNORLAND NEA 155CERN/GDD

CERN/GDD

CERN/GDD

CERN/GDD

Source

BAD

BAD

BAD

Result

YESYESDURALCO 4525

-

YES

Effectin

G.D.

YESHEXCEL A40

YESDURALCO 4461

OutgasProduct

Outgassing room-T epoxies

Fred Hartjes 19


Field geometry of most common gaseous detectors

Micromegas: homogeneous amplification field across 50 µm

Y. Giomataris et al, Nucl. Instr. and Meth. A376(1996)239 Y. Giomataris et al, Nucl. Instr. and Meth. A376(1996)239 F. Sauli, Nucl. Instr. and Methods A386(1997)531F. Sauli, Nucl. Instr. and Methods A386(1997)531

GEM: amplification field across ~ 25 µm (high at the edges of the hole)

Anode NOT close to avalanche

Wire chamber: 1/R amplification field

MSGC: dipole amplification fieldVery high field at

cathode edge

ANODE STRIPANODE STRIP

CATHODE STRIPSCATHODE STRIPSA.Oed, Nucl. Instr. and Meth. A263(1988)351 A.Oed, Nucl. Instr. and Meth. A263(1988)351

50 µ

m

Fred Hartjes 20


Dependence on detector technology

Polymerisation will be mainly at the end of the avalanche where the electron density is highest A few µm away from the anode

Exception: GEM

Key issue Whta is the field at the anode surface?

High field => high avalanche temperature

=> more dissociation organic molecules

=> more sensitive to ageing

How big is the anode surface near avalanche? MSGC: very small (edge of anode strip)

Wire chamber: quite small

Micromegas: large

GEM: avalanche not in vicinity of anode

=> GEM and Micromegas less vulnerable for ageing

Field strength (E) along the central drift path (X) to the anodefor three different electrode geometries

X (m)

0 20 40 60 80 100

E(k

V/m

m)

0

10

20

30

40

Wire chamber

MSGC

Micromegas/InGrid

MSGC ageing:In the µC/cm range

Fred Hartjes 21


Interesting example of wire chamber ageing:Production of LHCB straw tracker

Tracker from boxes filled with straws (Ar/CO2 70/30)

Uniformity of response automatically scanned with a 90Sr source across the full surface

Radhard test during production Scan Single point irradiation with a 2 mCi 90Sr source (20 h)

accumulated charge 2.8 mC/cm (peak value)

Verification scan

Ref:, Ageing in the LHCb Outer TrackerNiels Tuning (Nikhef)IEEE NSS (N48-3) Nov. 1, 2007

Irradiation profile across the straws

Fred Hartjes 22


Result

At accumulated charge 2.8 mC/cm (peak value)

Strong unexpected ageing effect No ageing downstream

At prototype tests no ageing observed Until 3 C/cm

Gas flow

2nd scan /1st scan

Accumulated 3 C/cm in 120 days

No effects seen

Fred Hartjes 23


Intensity dependence of ageing

Strongest ageing at moderate intensity Not much ageing at the highest intensity

=> not proportional to accumulated charge

Highest ageing at ~ 0.2 mC/cm

Deposit on wire surface visible

Deposit on the surface?

Fred Hartjes 24


Cause of the LHCB ageing phenomenon

Analysis of wire deposit Carbon, no silicon

Culprit: fresh glue Araldite AW103 + HY991 On the green CERN material list

Analysis of wire deposit

Carbon

In UseNONOTRABOND 2115ATLAS/TRT

In UseNONOARALDITE AW103(Hardener HY 991)

CERN/GDD

ATLAS/TRT

In UseNONOECCOBOND 285HERA-B/ITR

CERN/GDD

HERA-B/OTR

CERN/GDD

Source

Out ofproduction

In Use

Longcuring time

Note

NONOHEXCEL EPO 93L

NONOSTYCAST 1266(A+Catalyst 9)

NO

Effect inG.D.

NOSTYCAST 1266(A+B)

OutgasProduct

Fred Hartjes 25


Possible curing method: HV training HV training

24h @ 10 µA/wire After training plateau occurs of ~ 30 mC/cm

Comparable effect seen by Blinov in DME Plateau ~ 300 mC/cm

=> plateau caused by plasma cleaning of anode surface?

2nd HV training

1st HV training

3rd HV training R

elat

ive

Gai

n

Irradiation Time (hours)V. Blinov,V. Blinov, I. N. Popkov, A. N. Yushkov, I. N. Popkov, A. N. Yushkov, Aging measurements in

wire chambers, Nucl. Instr. and Meth. A515(2003)95 , Nucl. Instr. and Meth. A515(2003)95

Fred Hartjes 26


Possible curing method: outgassing

Outgassing Heating up for 2 weeks @ 45ºC

or Flushing for ~6 months

Preventing ageing by O3

2.5% O2 added

=> O3 formed in the avalanche

Less ageing with low flow Gas cleaned by avalanche

G

ain

loss

(%

)

Flushing Time (weeks)

Fred Hartjes 27


Comparing MPGD ageing to silicon sensor ageing

Gaseous detectors might be much more radhard

but Silicon sensor ageing

Can be well characterised in lab conditions Results relatively easy to scale up to a big tracker setup

Testing samples of the final production batch at various particles Lab measurements give a good prediction

Gaseous detector ageing Characterising gaseous detector ageing by the ageing rate parameter R (%/C/cm) alone is a too

simple approach Lab characterisations at different sites often conflict Too many parameters involved

Particle type Gas purity Cleanliness of the gas system Irradiation rate (we cannot cope with every rate) Irradiated surface ............

there is always a risk when running a big tracker system with gaseous detectors Gaseous detector ageing might suddenly occur and proceed very fast

Ageing tests with Micromegas and GEM have not reached the silicon limit yet many ageing studies to be done

Fred Hartjes 28


General recommendations

For a big experiment it is hard to exactly reproduce the laboratory conditions that

were used for the ageing tests

Be very alert on unexpected ageing phenomena

Experience on ageing from other groups is helpful, but don’t take it too absolute

Everybody has its own ageing experience, they don’t reproduce well for other sites

and with other detectors

Take notice of the experience of plasma physicists

But I haven’t seen an explanation for ageing caused by extremely low pollutant levels in

gaseous detectors

Fred Hartjes 29


Design recommendations

Reduce field on cathode surface as much as possible

Use the cleanest materials you can afford (NASA and CERN database)

But there’s no need getting bankrupt

Add filter at the in coming gas close to the detector (molecular sieve 5A)

Consider adding special ageing chamber for advance cleaning (see LHCB

experience)

But don’t expect this to be absolutely safe to prevent ageing

Do as much ageing prototype tests as you can on as much different conditions to

get an impression of the robustness of your detector

Different particles

Different irradiation rates

Different sites

Fred Hartjes 30


Operational recommendations

While running, monitor the chamber performance on a daily basis and take

immediate action when observing ageing phenomena

Don’t change from gas supplier while running an experiment

Be prepared to apply additives

CF4 + oxygen containing molecule like CO2 or alcohols

Water (active moisture control and monitoring), don’t let it pass the 1% limit

=> But be aware that these measures might worsen the situation in your specific

case

Fred Hartjes 31


A last word of encouragement

After a lot of testing you will get to know the characteristics of your own system

quite well

You will learn how to operate it safely and to avoid unexpected ageing

Fred Hartjes 32


Studying MPGD ageing?

Magic in a scientific environment

Fred Hartjes 33


Spare

Fred Hartjes 34


Possible ionisation sources for ageing studies

PS beam at CERN Best radiation test Mip ionisation profile (24 GeV/c p) Average rate 3 - 9 GHz/cm2

but current during spill order of magnitude higher (> 50 GHz/cm2) Can Gossip handle this??

Running a testbeam experiment is time and money consuming Tight time schedules

Powerful (5 GBq) 90Sr source at Nikhef Up to ~ 1.5 GHz/cm2 continuously Rate still OK for Gossip Mip ionisation profile (1 – 2 MeV/c e-) simulating b-layer environment Always available Not ultimate radiation test

UV light source at Nikhef (Harry van der Graaf) Continuous operation Easy in use (no personal danger) Different ionisation profile

individual photoelectrons mainly liberated from metal surfaces

Reference: pixel b-layer at SLHC rate up to 0.4 GHz/cm2

dose up to 1016 cm-2

mostly hadrons: p, in GeV range (mips) (MeV - GeV range) n (MeV range)

Fred Hartjes 35


Irradiation facility with 5 GBq source

Remote controlled irradiation stage Sample can be moved in and out by

pneumatic piston => separating induced signal from

background signal

Ageing sample

source

Fred Hartjes 36


90Sr source at Nikhef

5GBq 90Sr 1 – 2 Mev e- simulating mips

Rate calibrated with ionisation chamber

Distance sample to source 4.7 mm => 1.33 GHz/cm2 (sphere) 1.25 GHz/cm2 (parallel surface)

=> 1.15*1014 mips/cm2/day in bulk material

SLHC aim: 1016 mips/cm2 for the ATLAS b-layer

Fred Hartjes 37


Dummy detector for GOSSIP ageing studies

Dummy glass ROC Circular pads on 60 µm pitch Drift volume 13 x 13 mm, 1.24 +/- 0.01 mm high Centre signal electrode: 2 x 2 mm structure of 1089

pads (red) => Final detection volume is a block of 2 x 2 x 1.2 mm

Gas gain by Micromegas Closed gas volume of 210 µl Gas flow ~ 0.5 l/h

=> more than 2000 volume exchanges/hour

1.2

Cathode foil Micromegas Gas tube

Dummy ROC

16

Icentre electrode

Iguard electrode

Fred Hartjes 38


Source geometry during irradiation

Distance centre source to centre drift volume 4.7 mm Homogeneous irradiation of centre electrode

4.7drift cathode

Micromegas

Dummy ROC

2.0

centre electrode

Guard electrode

Ø5.01.0 5 GBq 90Sr source

1.2

Dimensions uniformly scaled

Fred Hartjes 39


Rate dependence

Gas gain of Gossip 23

Vgrid (-V)

500 520 540 560 580 600 620 640

I anod

e (n

A)

20

30

40

50

60

70

8090

200

10

100

G = 1000

Fit: y = 0.0047e0.0161

Ar/iC4H10 30/70

mip rate 1.15 GHz/cm2

27-11-07

Gas: Ar/iC4H10 70/30

Rate 1.33 GHz/cm2 Rate dependence

investigated by gain curve

No sign of saturation until gain = 900

Fred Hartjes 40


Ageing method Two gas mixtures tested so far

Gossip21: He/iC4H10 78/22

Gossip23: Ar/iC4H10 70/30

Data taking every 2s Background current periodically measured

for reference 20 s per 4 hour Part of the raw data

t (s)

0.0 2.0e+4 4.0e+4 6.0e+4 8.0e+4 1.0e+5 1.2e+5 1.4e+5 1.6e+5

I cen

tre

(nA

)

-400

-300

-200

-100

0

I guar

d (

nA)

-1500

-1000

-500

0

500

1000

1500

Raw data (detail)

t (s)

1.151e+5 1.152e+5 1.152e+5 1.153e+5 1.153e+5

I cent

re (

nA)

-400

-300

-200

-100

0

I guar

d (n

A)

-1500

-1000

-500

0

500

1000

1500

Icentre

Iguard

Centre current

Guard current

Fred Hartjes 41


Gossip21: He/iC4H10 78/22

Sept 07gain = 1100He/iC4H10 78/22


Time (days)

0 5 10 15 20 25 30 35

I cen

tre (

nA)

0

25

50

75

G = 1000 G = 1000

Fluence (mips/cm2)

0 1e+15 2e+15 3e+15 4e+15

No sign of decay of gas gain

Instabilities partly caused by

variations in temperature and pressure?

But measurement had to be terminated because of increased sensitivity for HV trips

Tripping induced by radiation

Vgrid = -418 VVcathode = -627 V

Fred Hartjes 42


Gossip23: Ar/iC4H10 78/22

More fluctuation but no significant indication for decay of gas gain

Trip (Iguard > 2 µA) at about once a week

Again measurement had to be terminated after 22 days because of increased sensitivity for tripping

Gossip 23Nov 28Ar/iC4H10 70/30

Particle flux: 1.6 GHz


Time (days)

0 5 10 15 20 25

I cen

tre (

nA)

0

100

200

G = 1000 G = 1000

Fluence (mips/cm2)

0 1e+15 2e+15 3e+15

switch fromVgrid = -635 to -640 V

Vgrid = -635 VVcathode = -889 V

Fred Hartjes 43


Linear fitI = I0 + a.ta = -0.5932=> a/I2 = 0.0183

av current = 5.9 A=> total charge deposited = 5.9*3600*24*4 = 2.55 Csurface 0.49 cm2

=> 5.2 C/cm2

assume: drift distance 1 mm Ar/CH4 having 9e-/mm=> 1 mip = 9*1000*1.6*10-19

= 1.44 10-15Cdeposited charge corresponds to3.6 1015 mips/cm2

X ray irradiation at PANalytical (detail)

Time

14-M

ay-0

5

16-M

ay-0

5

18-M

ay-0

5

I cath

(A

)

0

2

4

6

8

Icath

1/x fit

3.6x1015 mips/cm2@ gain = 1000

Comparison to earlier measurement 8.04 keV X-rays at

Panalytical Here 40% reduction in gain

but no tripping problems Using X rays instead of

MIPs? Anode: solid aluminium plate

instead of small pads glass ROC?

Gas: Ar/CH4 90/10 vs Ar or He / iC4H10 mixtures?

At Panalytical ~ 5x higher charge rate?

Much lower gas refreshment rate

Other reasons???

Fred Hartjes 44


Examining Gossip21 after irradiation

Field foil removed Coloured spot on top of Micromegas

near one of the gas pipes Probably inlet

When removing Micromegas no other pollutions/damages found Dummy ROC and Micromegas were

still clean

=> no visual cause for HV tripping traced

Fred Hartjes 45


Ageing test chamber with ionisation by UV light Initiated by Harry van der

Graaf Long, thin chambers from

clean materials SS glass ceramics No plastics, epoxies

Closed loop gas system Gas gain by InGrid

structure Inserting suspicious

material in test container Possible purification of the

gas by avalanches Downstream chambers

have less ageing (LHC-b experience)

Still in development

Test container

Quartz window

Fred Hartjes 46


Conclusions

For the Gossip prototypes we do not see the common ageing behaviour of gaseous detectors No significant decrease of gas gain even at a high dose But for iC4H10 mixtures deterioration of HV stability

Not in agreement with earlier X-ray CH4 test for unknown reasons

Will continue tests with other quenchers CO2

DME CH4

Verification required with other kinds of irradiation (hadrons, , n)

SiProt ageing looks promising No significant effect observed until 4 *1015 cm-2

Protection and ROC operation remain intact To be repeated with neutrons

UV light ageing Convenient experimenting Easy way tracing ageing compounds

Fred Hartjes 47


spare

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Fred Hartjes 1 2 nd RD51collaboration meeting, Paris, October13 - 15, 2008 MPGD ageing Fred Hartjes...

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