M. Capeans 1 International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg) Materials and gases: Lessons for detectors and gas systems Mar Capeans CERN Invited review talk at the International Workshop on Aging Phenomena in Gaseous Detectors
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M. Capeans 1International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Materials and gases:Lessons for detectors and gas systems
Mar CapeansCERN
Invited review talk at the International Workshopon Aging Phenomena in Gaseous Detectors
M. Capeans 2International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Outline
• Ageing• Outgassing studies• Detector Assembly Materials• Detector Assembly Procedures• Components for Gas Systems• Influence of Some Gases on Ageing
M. Capeans 3International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
The Very Basic Knowledge
• Gaseous detectors operated in a high radiationenvironment can have serious operational problems dueto ageing.
• Commonly ageing manifests as:– Loss of gas gain– Worsening of energy resolution– Excessive currents– Self-sustained discharges– Sparking
All these are usually related to the presence of depositscoating the electrodes (anode and/or cathode).
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 4International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Basic Knowledge
• The ageing process is due to very complex phenomenathat take place during the gas avalanche (~ plasmachemistry).
• These phenomena lead to the creation of a wide variety ofspecies that may accumulate as deposits, conductive orinsulating, on the electrode surfaces.
GasesGas systemsProceduresMaterialsStudiesAgeing
Polymers• Solid, highly branched and cross linked• Excellent adhesion to surfaces• Resistant to most chemicals• Insoluble in most solvents
Polymerization
M. Capeans 5International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Basic Knowledge
• Measured ageing, quantitative and qualitatively,depends on many factors:
• Gas gain• Gas flow & Pressure• Charge density• Geometry and configuration of electric field• Active gas
• Experimental observations are difficult to compareand/or extrapolate between one another.
Nature of gasTraces of contaminants
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 6International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
ATLAS-TRT, ATLAS-MDT, CMS CSC,…Detector R&D for LHC
RD-28, Hera-B, CMS, ATLAS,…MSGC community
RD-10, RD-28, RD-6,…Basic R&D
DELPHI,…LEP @ CERN
SDC Straw tubes, Pad chambers,…SSC @ US
Still comparison and/or extrapolation is difficult butall this experience provides a solid basis for discussion
1986
1990
1994
M. Capeans 7International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Contributions to the Ageing Process
Radiation(structural changes)
PollutantOutgassing
MATERIALSReactive/SolventGases
Uncontrolled Pollution(gas cylinders)
PolymerizingMixtures
ReactiveAvalanche Products
GAS
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 8International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Outgassing Tests of Some Materials
GasesGas systemsProceduresMaterialsStudiesAgeing
Outgassing studies
ContaminationRigid Materials
Adhesive tapesLeak Sealers
Epoxy compounds •Low outgassing, Room T curing•Rejectable, Room T curing•Curing at T > 40 co•Conductive
•User-generated•Silicone
•Methods
M. Capeans 9International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
The Minimal Set-Up
AnalysisStation
OutgassingBoxGas in
PRE-SELECTIVE
CHARACTER
GasesGas systemsProceduresMaterialsStudiesAgeing
• Impurity detection has the intrinsic limitations of the analysisstation, that may not be sensitive to all species because of:
• low pollutant concentration• specific sensitivity
• Sometimes heating of the sample is needed to detect outgassing(scaling factor unknown).
• Even if outgassing is detected, it might not be harmful for thegaseous detector.
Gas analysis of a sample
M. Capeans 10International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Gas Chromatography BasicsGasesGas systemsProceduresMaterialsStudiesAgeing
CarrierGas ECD
Gas inGC
MSD
GC: oven with a capillary column.Function: it separates gas substances dependingon their interaction properties with the column.Signal: a signal appears for each separatedcompound at some retention time, defined by thecolumn and temperature profile.
MSD: 70 eV e- source to ionize andfragment molecules + quadrupolemass filter to sort resulting ionsaccording to their M/Z ratio.Function: it identifies eachmolecular compound.Signal: ion abundance as function ofretention time in the column or M/Zratio.Sensitivity: ~ ppm
ECD: βe- bombard a carrier gas to form aplasma. Thermal e- are collected applying anE-field. The decrease of the detector currentdue to removal of thermal e- byrecombination in presence of electro-capturing compounds gives a signal.Function: detection of electronegativesubstancesSignal: signal amplitude vs. time.Sensitivity: ~ ppb
M. Capeans 11International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Gas Chromatography BasicsGasesGas systemsProceduresMaterialsStudiesAgeing
Selection of column, temperature profile and carrier gas natureand flow defines the sensitivity of the station.
MSD signal 10 ppm F12+F11 ECD signal 10 ppm F12+F11
M. Capeans 12International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Gas Analysis + Detector irradiation
To get information about the effect of pollutants:Gas Analysis + Ageing Test
Clean Gas detector(full metal SWPC orany other validated device)
Small prototype of final detector
AnalysisStation
Gas in
GaseousDetectors
Limitations: - Irradiation conditions (high dose rates)- Time scale (~months)
OutgassingBox
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 13International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
• Developed at NASA to search low outgassing materials forspacecraft use.
http://epims.gsfc.nasa.gov/og/index.cgi
• Test of conditioned micro-quantities in vacuum at statedtemperatures and specific times.
• Technique of condensing the volatile products to determine theamount of volatile condensable materials.
Parameters to take into account during selection:• Shear strength• Elongation at break• Viscosity• Electrical properties• Capillary effect• Radiation resistance• Outgassing
•Material itself•User-generated (hard to trace):
– Pollution – Incorrect ratio of hardener to resin– Insufficient mixing– Insufficient curing time
M. Capeans 15International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Low Outgassing Epoxy CompoundsRoom-T Curing
GasesGas systemsProceduresMaterialsStudiesAgeing
In UseNONOTRABOND 2115ATLAS/TRT
In UseNONOARALDITE AW103(Hardener HY 991)
CERN/GDDATLAS/TRT
In UseNONOECCOBOND 285HERA-B/ITR
CERN/GDD
HERA-B/OTR
CERN/GDD
Source
Out ofproduction
In Use
Long curingtime
Note
NONOHEXCEL EPO 93L
NONOSTYCAST 1266(A+Catalyst 9)
NO
Effect in G.D.
NOSTYCAST 1266 (A+B)
OutgasProduct
M. Capeans 16International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
‘Rejectable’ Epoxy Compounds Room-T Curing
GasesGas systemsProceduresMaterialsStudiesAgeing
BADYESARALDITE AW 106(Hardener HV 935 U)
CERN/GDDATLAS/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
M. Capeans 17International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
TESTS OF ARALDITE AW 106 (+HV953U)
GasesGas systemsProceduresMaterialsStudiesAgeing
10-13
10-12
10-11
10-10
10-9
0 20 40 60 80 100
Araldite 103_2 Araldite 106
Ion
Cu
rren
t (A
)
Mass
C. Bellachioma, E.Broilo, P. Chiggiato, M. Van StenisCERN
H2O
O2
CO2
CO
xylenehexane
trimethylpentane
trimethylbutane
butane
TML 3.26% CVCM 0.02%
AGEING
TEST
NASA TEST
(@CERN)
GC+MSD
ION
Analyzer
M. Capeans 18International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Epoxy Compounds Curing at T > 50 oC
GasesGas systemsProceduresMaterialsStudiesAgeing
BAD
BAD
BADBADOK
OK
OKOK*OK
Result
-NO60RUTAPOX L20ATLAS/TRT
-NO65POLYIMIDE
DUPONT 2545CERN/GDD
NOYES*65EPOTEK H72HERA-B/ITR
-NO85AMICON 125CERN/GDD
NOYES50EPOTECNY E505 SITCERN/GDD
YES70ARALDITE AW 106CERN/GDD
50
65
Curing T(oC)
YESYESLOCTITE 330CERN/GDD
-YESNORLAND UVS 91CERN/GDD
CERN/GDD
Source
YES(Silicone)EPOTECNY 503
Effect inG.D.OutgasProduct
M. Capeans 19International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Conductive Epoxy Compounds
OKNONOTRABOND 2902ATLAS/TRT
HERA-B/OTR
CERN/GDD
Source
OK
OKResult
NONOSILBER LEITKLEBER3025 (A+B)
Effect in G.D.NOTRADUCT 2922
OutgasName
GasesGas systemsProceduresMaterialsStudiesAgeing
BAD-YESTESAFIX 4388HERA-B/OTR
HERA-B/OTR
Source
BAD
Result
-YESSCOTCH 467 MP
Effect in G.D.OutgasName
Adhesive Tapes
M. Capeans 20International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Outgassing Tests of Leak Sealers
HERA-B/OTR
CERN/GDD
CERN/GDD
CERN/GDD
Source
OK ?NOin very small quantities
YESSilicone basedDOW CORNING
R4-3117 RTV
BAD-YESPolyurethane-based
LOCTITE5220
OK ?NOin very small quantities
NOCaoutchoucSilicone RTV
RHODORSILCAF4
NO
Effect inG.D
OKNOSolvent-freeepoxy resin
VARIANTorr-Seal
GlobalResultOutgasTypeMaterial
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 21International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Consult NASA database to select materials, before doing the time-consuming testsNASA Database: More than 1600 entries for adhesives, 500 entries for rubbers and elastomers,800 entries for potting compounds, etc…
OKOKOKKalrezOKOKOKVECTRA 150
BADBADEpotek 905
OKOKOKULTEM
OKOKOKEccobond 285
OKOKBADStycast 1266
OKOKOKNuvovern LW PUR
Ageing testGCNASASAMPLE
BADBADDow Corning RTV
BADBADBADAraldite 106OKOKBADAraldite 103
M. Capeans 24International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Possible Sources:• Silicone rubber sealants• Silicone potting and encapsulation
metasilicate)• Glass and related products (glass fibres
used for reinforcing resins)
3
3
Silicone Contamination
• Silicone has been systematicallyfound coating aged chambers.
• Silicone has a high natural affinityfor most materials.
• Silicone has the tendency tomigrate.
• Silicone is relatively inertchemically and unaffected by mostsolvents, therefore among the mostdifficult surface contaminants toremove.
• Silicone is etched away by F-species.
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 25International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Accidental Silicone Contamination
Wheel 2, straw p96g1c06 after 14 hours irradiation
320
330
340
350
360
370
380
0 5 10 15 20 25 30 35 40
R, cm
Mea
n A
mpl
itude
0
5
10
15
20
25
30
35
40
D
M
M
D
D
ATLAS/TRTS. Mouraviev
CERN
ATLAS/TRTS. Mouraviev
CERN
~ 10 % gain loss
Amplitude
E Resolution
GasesGas systemsProceduresMaterialsStudiesAgeing
Wea
k 55
Fe ~
700
Hz
M. Capeans 26International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Silicone Contamination
Si depositSi deposit
Si depositSi deposit
Region between two irradiated spots
Irradiated spotClean wire
Silicone Source:Silicone-based lubricant used accidentally during straw tubemanufacturing by the manufacturer.Mass production straws are free of pollution (no lubricant at all).
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 27International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Silicone Contamination: Si-bubbler
GasesGas systemsProceduresMaterialsStudiesAgeing
Add Silicon-oil bubblerto chamber exhaust
MSGC inclean gas system
GDD GroupCERN
GDD GroupCERN
M. Capeans 28International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Detector Assembly Procedures
Contaminants during the assembly process such asdust particles or an invisible film of organic material can
make the best-designed detector fail.
Assembly Procedures
EquipmentPersonnel
Assembly area
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 29International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Det
ecto
r: dr
ift tu
bes o
f sm
all d
iam
eter
Gas
: Ar-
CO
2-C
F 4R
ate
~ 3x
105 H
z/cm
2 , do
se ~
100
kra
d/y
Assembly Area
The assembly area must be isolated from othermanufacturing areas, and usually following clean roomstandards.
4 assembly sites located worldwide:Nb. of particles > 0.3 µm in a 0.1 cubic foot of air Hera-B/OTR
DesyHera-B/OTR
Desy
Area 1: 1 - 20Area 2: 1 - 15Area 3: 760000 Area 4: 520000
Office: 440000Std hall: 770000
GasesGas systemsProceduresMaterialsStudiesAgeing
All modules behaved equally well during HV testingand running in the Hera-B environment.
WHICH
LEVEL?
M. Capeans 30International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Equipment
Some equipment should be avoided or protected
Examples of contamination are:• Tools with lubricated shafts, cranes…• Soldering or brazing equipment that require heating of
volatile fluxes• Motors and vacuum pumps with outgassing oils• Some electronic equipment contain capacitors, resistors,
etc coated with organic or insulating materials thatoutgas
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 31International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Personnel
Usual source of contamination.Need careful and exhaustive training.
Examples of contamination are: • Street clothing (source of lint)• Hair, make-up, fingernails (source of oil and
particulates)• Many hand creams and cosmetics (contain silicones)• Saliva• Fingerprints (source of fat, possible cause of corrosion
in some metals, etc)
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 32International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Assembly process
It has to:
• Be well specified and stable• Be rechecked periodically• Include specification for the storage of parts• Include procedures about:
– cleanliness of assembly components– verification of cleanliness
• Include tracing capability– operator ID, assembly step, material batch,
environmental parameters, etc
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 33International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Ageing test of the same MSGC (Ar-DME 90-10)in 2 gas systems
1ultra-cleanfull metalKemraz
2standard cleanliness
Viton jointsstd metal valves
Cu-exhaustTorr-Seal sealing
GDD GroupCERN
GDD GroupCERN
M. Capeans 37International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Valves
GasesGas systemsProceduresMaterialsStudiesAgeing
Systematic study (GC) to search the origin of pollution
• Isolate components of the std.gas system
• Manual SS ball-valve (PFTEjoint) found suspicious
Freon 113Contamination
• Take valve to ultra-cleansetup
• Ageing Test + acceleratedrate of outgassing
M. Capeans 38International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Search for Clean Components
The ATLAS-TRT approach:
• Problem:
straw tubes are very sensitive to silicone pollution
• Approach: use only clean componentsMarket-survey to look for clean gas components equivalent toultra-high purity standards in terms of very low outgassingrates and absence of lubricants (especially silicone-based).The requirements have to be discussed with the companies.
ATLAS/TRTCERN
ATLAS/TRTCERN
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 39International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
M. Capeans 40International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Pressure Regulators
~ 300 - 600Standard applications:They might be certified lubricant-free by suppliers… For safety, theyalways need additional cleaning
>1000
~ 600
High purity applications:Lubricant-free certified, but experience tell us that it might NOT be true.Some companies produce affordable, clean products:TESCOM (serie04)
> 2000
~ 600
Ultra-high purity applications (semiconductor industry):Lubricant-free certified & excellent surface quality.Reducing our requirements (in terms of surface quality):- Brass option at SCOTT Specialty Gases (model C21-8)-Parker Veriflo line (model IR4002)
Price CHFKnowledge
Studied in detail 15 different models from ~10 companies.
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 41International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Pressure Regulators
Validation of P-regulator dual stageSCOTT C21-8
Straw 2
0.95
0.97
0.99
1.01
1.03
1.05
0 100 200 300 400 500 600 700Time (hours)
Rel
ativ
e ga
in
ATLAS/TRTCERN
ATLAS/TRTCERN
Irradiated straw
GasesGas systemsProceduresMaterialsStudiesAgeing
Monitor straws
M. Capeans 42International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Flowmeters
• When possible, use electronic mass flowmeters with theadequate O-rings.
• Mechanical flowmeters: Cheap BUT Assembled with lubricants
PNPI straw 3
0.550.6
0.650.7
0.750.8
0.850.9
0.951
1.05
0 100 200
Time, hours
Gas
gai
n va
riatio
n
Series1
VOEGTLIN FlowmeterType V100 (CERN std.)Inserted in gas stream
ATLAS/TRTCERN
ATLAS/TRTCERN
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 43International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Flowmeters
Cleaning flowmetersUltrasonic cleaning of dismounted pieces.
Straw 3
0.9
0.95
1
1.05
1.1
0 50 100 150 200 250
Time (hour)
Rel
ativ
e G
ain
Gap 1/4
Gap 2/4
Gap 3/4CLEANED VOEGTLIN Flowm.Type V100 (CERN std.)Inserted in gas stream
ATLAS/TRTCOMPASS
CERN
ATLAS/TRTCOMPASS
CERN
Irradiated straw
By M.Bosteels (CERN):
15’ Ultrasonic bath Isopropyl alcohol15’ Ultrasonic bath Isopropyl alcohol15’ Ultrasonic bath ultra pure water20 h at 70-80 oCREM
OVES GREASE
!
GasesGas systemsProceduresMaterialsStudiesAgeing
Monitor straws
M. Capeans 44International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Connectors
Unions, elbows, nuts, etc…
Certified lubricant-free.If additional SC-11 cleaning, price is 25% higher.
SWAGELOK
To avoid ‘risk of contamination’ items should be orderas “oxygen degreased“ (= acetone baths).Price: + 20%
SAGANA
Risk of paraffin contaminationGYROLOK
NoteCompany ATLAS/TRTCERN
ATLAS/TRTCERN
GasesGas systemsProceduresMaterialsStudiesAgeing
Mount system following clean procedures: protective clothing, clean storage, no open ends, etcFollow manufacturer directions to the letter
Never mix one brand or metal with another one
BASICS
M. Capeans 45International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Piping
Plastic Pipes: PTFE, NYLON, PVC, PU, etc
• Metal Pipes: Copper, Stainless Steel
InsulatingElasticCheapLow density
High gas permeabilityHigh desorption rate
0 gas permeability0 outgassing
ExpensiveDifficult handling
CLEANING
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 46International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Outgassing Tests of Plastic Pipes
BAD-YESPolyetheretherketone
PEEKAmorphous
OKNONOPolyetheretherketone
PEEKCrystalline
OK*NOWaterPolyamideRILSANNYLON
-
-
NO
Effect inGaseous Detector
BADYESPolyurethanePUR
BADYESPEE
OKNOPolypropylenePP
GlobalResultOutgasTypeMaterial
GDD GroupCERN
GDD GroupCERN
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 47International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Water v. & Nylon PipesGasesGas systemsProceduresMaterialsStudiesAgeing
Gasdetector
25 m Cu
+ 20 m Nylon Pipe~ 1700 ppm H2O
GC/MSFreon11 DME
Freon11DME
H2O
GasinEC
D si
gnal
ECD
sign
al
M. Capeans 48International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Outgassing Tests of Elastomers
BAD-YESFluorinatedpolyvinyldenePVDF
BAD-YESCopolymer
ethylenepropylene
EPDM
BADYESYESFluorinatedcopolymerVITON
NO
Effect inGaseous Detector
OKNOFluoropolymerKALREZ
GlobalResultOutgasTypeMaterial
GDD GroupCERN
GDD GroupCERN
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 49International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
About system components…
• It is common to find that manufacturingspecifications and product descriptions donot contain enough information.
• Once an adequate product has been found,it is difficult to asses the cleanlinessconditions for large quantities.
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 50International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
• Define your cleanliness requirements• Avoid pollution during assembly• Flush gas through the open system
The Golden Rule
AS SOON AS POSSIBLEAS MUCH AS POSSIBLE
GasesGas systemsProceduresMaterialsStudiesAgeing
M. Capeans 51International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Influence of Some Gases on Ageing
GasesGas SystemsProceduresMaterialsStudiesAgeing
DME & CO2
CF4
Hydrocarbon mixtures
M. Capeans 52International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
HydrocarbonsPolymerization guaranteed
• Polymer formation directly in the avalanche process.• Effect is more pronounced under spark/discharges.
GasesGas SystemsProceduresMaterialsStudiesAgeing
GDD GroupCERN
GDD GroupCERN
M. Capeans 53International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
• CF4 dissociates in F and CFx radicals (~ stable species).XR
2 MHz/cm
XR~Hz/cm
Straw tube4mm diam.
SWPC~ 3 cm drift
Xe-CO2-CF450-30-20
SWPC Pulse height
• They have enough energy to break chemical bonds in polymers.• Polymer is reduced to stable, volatile products.• These products are removed from electrodes by the gas flow.
M. Capeans 62International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
• The long-term capability of a detector can only be extrapolated toreal conditions if final prototypes are:
• Tested under conditions as close as possible to the final ones, and strictlycontrolled
• Large irradiation area & charge density as close as possible to finalexperiment
M. Capeans 65International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Conclusions on Materials• There is no good or bad material. A material is adequate or not for a
very particular type of detector and conditions of use.
• Existing data, obtained either from systematic outgassing studies orexperience gained with detectors, has only a pre-selective character.
• A list of low outgassing assembly materials exists, that includes epoxycompounds, rigid materials, sealants, elastomers, …
• The effect of materials that outgas at the ppm level has to be tested foreach particular case. That is the case for materials such us Viton, Teflon,Polyurethane, etc
• It seems rather universal that Silicone compounds that easily migrate(lubricant-type) should be avoided, especially with some gas mixtures(F species).
M. Capeans 66International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)
Conclusions on Gases• Noble Gas + Hydrocarbon:
– Not trustable for long-term high rate experiments– It is accepted that oxygen containing additives can improve detector
lifetime in such mixtures
• Noble Gas + DME:– They are radiation hard when careful material selection has been done– Halogen contamination at ppb level shortens detector lifetime. It is difficult
to monitor
• CF4 -containing mixtures:– They are very attractive in terms of ageing due to the fine polymerization-
deposition balance phenomena– They need strict control of pollutants (H2O)– F-radicals are rather stable and able to attack some materials. They are
capable of etching away Si-compounds that may trigger strongpolymerization processes
M. Capeans 67International Workshop on Aging Phenomena in Gaseous Detectors October 2-5, 2001 at DESY (Hamburg)