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Fred Hartjes 1
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
MPGD ageing
2nd RD51 collaboration meetingParis, October 13 - 15, 2008
Fred Hartjes 2
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
Gossip ageing using mips from 90Sr source
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
Studying MPGD ageing?
Magic in a scientific environment
Fred Hartjes 33
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
Spare
Fred Hartjes 34
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
Gossip21: He/iC4H10 78/22
Sept 07gain = 1100He/iC4H10 78/22
Gossip ageing using mips from 90Sr source
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
Gossip ageing using mips from 90Sr source
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
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
2nd RD51collaboration meeting, Paris, October13 - 15, 2008
spare