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Summary and Results of the

Summary and Results of the. Marcus Hohlmann Florida Institute of Technology (FIT) on behalf of the Workshop Organizing Committee (M.Hohlmann, C.Padilla, N.Tesch, M.Titov). March 2, 200 2 Budker Institute, Novosibirsk. LBL workshop 1986:. DESY workshop 2001:.

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Summary and Results of the

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  1. Summary and Results of the Marcus Hohlmann Florida Institute of Technology (FIT) on behalf of the Workshop Organizing Committee (M.Hohlmann, C.Padilla, N.Tesch, M.Titov) March 2, 2002 Budker Institute, Novosibirsk

  2. LBL workshop 1986: DESY workshop 2001: High Energy Physics experiments are currently entering a new era which requires the operation of gaseous particle detectors at unprecedented high rates and integrated particle fluxes. New classes of a gaseous detectors such as large scale straw-type detectors, Micro-Strip Gas Chambers, Micro-Pattern Gas detectors, and related detector types with their own specific aging effects have evolved since the first aging workshop at LBL Berkeley, in 1986. In light of these developments and as detector aging is a notoriously complex field, the goal of the worskhop was to provide a forum for interested experimentalists to review the progress in understanding of aging effects and exchange their recent experiences. M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  3. International Workshop on Aging Phenomena in Gaseous Detectors ~ 100 gas. detector experts Scientific program: 10 invited talks , 31 contributed talk, 9 posters J.Va’vra, ``The Basics on Aging and the Early Developments since the 1986 Workshop’’ H.Yasuda, ``New Insights into Aging Phenomena from Plasma Chemistry’’ M.Capeáns, ``Aging & Materials: Lessons for Detectors and Gas Systems’’ C.Padilla, ``Aging Studies for the Outer Tracker of HERA-B’’ A.Romaniouk, ``Aging Studies for the Transition Radiation Tracker of ATLAS’’ T.Hott, ``Aging Problems of the Inner Tracker at HERA-B’’ V.Peskov, ``Aging in Gaseous Photodetectors’’ D.Marlow, ``Recent Experiences with Aging In Systems of Resistive Plate Chambers’’ F.Sauli, ``Review of Results on the Fundamental Understanding of Aging Processes’’ B.Schmidt,``Recommendations forthe Next Generation of Gaseous Detectors’’ M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  4. Introduction to Wire Chamber Aging A permanent degradation of operating characteristics under sustained irradiation, has been and still remains the main limitation to their use in high-rate experiments 1972 • ‘Classical Aging Effects’ lead to deposition of polymers on the • anode (and/or) cathode surfaces and manifest themselves as: • Loss of gas gain and reduction of the plateau region • Loss of energy resolution • Excessive currents • Self-sustained current discharge • Sparking M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  5. Polymer formation in wire chambers Whereas most ionization processes require electron energies > 10 eV, the breaking of chemical bonds and formation of free radicals requires ~ 3-4 eV During gaseous discharges many molecules break up due to collisions with electrons, de-excitation of atoms, and UV-absoprtion processes Free-radical polymerization seems to be a dominating mechanism of the wire chamber aging Polymer deposition mechanism (chemistry of gaseous discharges and nearby electrodes) • Chemical reactions between polymer • atoms and atoms of the electrode material • Electrostatic attraction to the electrode • (many chemical radicals are expected to • have permanent or induced dipole moments) Modification of electric field (J. Va’vra - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  6. Anode Wire Deposits Solid whisker formation:J. Kadyk, NIMA300(1991) 436-479 M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  7. Plasma Polymerization Plasma polymers are formed by coupling of free radicals Rapid Step-Growth polymerization mechanism (RSGP): Types of monomers and their polymerization characteristics: Type 1: Triple bond, aromatic & hetero aromatic Type 2: Double bond, cyclic Type 3: Linear & branched aliphatic Type 4: Oxygen-containing aliphatic Polymerization rate: Type 1 > Type 2 > Type 3 > Type 4 (H. Yasuda - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  8. Wire Chamber vs Plasma Chemistry Parameters are vastly different in two fields: J.Va’vra, NIMA252(1986)547-563 Some conclusions from plasma chemistry proved to be directly applicable to the wire chambers: (H. Yasuda, Plasma Polymerization) The structure of plasma polymer can not be uniquely related to the structure of monomer (Example: monomer C2H4) The most reactive fragment is assumed to be CH2: • Most organic compounds with • oxygen-containing groups are generally • reluctant to form polymers • Polymerization and chemical etching • in CF4-based gas mixtures • Overall mechanism of • Competitive Ablation and Polymerization M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  9. Competitive Ablation and Polymerization (H. Yasuda - Aging Workshop 2001, DESY) Ablation Polymerization Both polymer-forming species and species that cause the ablation of materials are created in plasma of the original monomer. ( Chemical ) Ar 0 - O2 +++ - H2O + - CO2 + - CH4 0 polymerize CF4 +++ - CF4+H2 0 (HF) polymerize CF4+CH4 0 (HF) polymerize CF4+CO2 ++ - Perfluorocarbons represent the most extreme case of ablation competiting with polymer formation CF4-based gases are used for both etching and deposition processes, the distinction being made by the gas and its concentration with which CF4 is mixed Respective contribution depends on the conditions of discharge M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  10. Details of polymerization: what is produced in Wire Chamber? GC analysis of compounds formed in wire chamber avalanches may help to understand the basic chemical processes causing aging effects in Ar/hydrocarbon mixtures. Plasma chemistry: Compounds with double or triple bonds can be easily ‘open’ and may start to form longer molecular chains Polymerizes very aggresively (K. Kurvinen - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  11. Aging Effects in Gaseous Detectors Implicit assumption: • aging rate is proportional only to the total accumulated charge R = - (1/G)(dG/dQ) (% per C/cm) (Kadyk’1985) This model is not proven for high intensity environments Aging phenomena depend on many highly correlated: • Macroscopic parameters: • Gas components • (nature of gas, trace contaminants) • Gas flow & Pressure • Geometry of electrodes • and configuration of electric field • Construction materials • Radiation intensity • Gas gain, current density • Size of irradiation area • Microscopic parameters: • Cross-sections • Electron or photon energies • Electron, ion, radical densities • … There are simply too many variables in the problem, and therefore it is too naive to expect that one can express the wire aging rate using a single variable such as Q/cm Much progress with these since 1986 LBL workshop M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  12. Aging Rate vs Current Density Summary of aging results with Ar/CH4 (90:10) in a laboratory setup (R. Bouclier et al., NIMA346(1994)114 ) • The aging rate can be a strong • functionof the current density Rate of aging (%,/C/cm) • The aging rate is independent • of the electrode materials and • purity of the methane; • (polymerization of CH4 itself) • The aging rate decreases if • water is added to the mixture Current density (nA/cm) How to extrapolate? Real operating conditions Accelerated aging tests (M.Capeáns - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  13. Recent experience with large detectors Radiation levels not even thought of in ‘1986: (from mC/cm many C/cm) ‘High radiation levels’ (LHC, HERA-B,…) ‘Low & standard radiation levels’ (LEP,HERA ep, BaBar,Belle,CDF,D0...) • Enormous R&D done • (RD-10, RD-28, RD-6, ATLAS-TRT, • ATLAS-MDT, CMS CSC, HERA-B OTR, • HERA-B ITR, HERA-B MUON,...) • Some basic rules are found • List of clearly ‘bad’ materials • Left only with a few gases • Most additives can not be used • in new detector types (MSGC, straw,...) • Basic rules for construction • are known and tested • Detectors are built and • demonstrated to work • Huge variety of gases • If aging is nevertheless observed : • add additives (H2O, alcohol) • (and/or) having identified the source of • pollution, try to clean the gas system Final proof of the large detector systems yet to come ! (B. Schmidt - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  14. L3 vertex drift chamber: Gas: CO2/iC4H10 (80:20) Collected charge ~ 0.1 mC/cm ZEUS Central Tracking Detector: Gas: Ar/CO2/C2H6 (83:5:12)+C2H5OH In run 2000: (after 7 years of operation) exponential current growth (Malter effect) No signs of aging effects during 11 years of LEP operation Cured by H2O additive • Possible reason: • Polymerization of hydrocarbons - • (oxygen containing additives might • improve detector lifetime) • No clear indication for the effect of gas • impurities or materials on the aging rate H1 Central Jet Chamber: Gas: Ar/C2H6 (50:50)+0.1%H2 O Collected charge ~ 10 mC/cm During 1996-2000: Some of the detectors shows gain reduction (and/or) Malter effect !!! Large system aspects: Normally identical detectors may behave very differently (H1 inner CJC vs outer CJC) Replacing 0.1% H2 0 with 0.8% C2H5OH cured the Malter effect Experience with 'standard' detectors (LEP, HERA ep) Low radiation levels: current density < 1nA/cm, Q ~ 0.1-10 mC/cm M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  15. Malter Effect Insulating layer • Malter effect is induced by insulating • deposits on the cathode Ions which are not neutralized at the cathode L. Malter, Phys. Rev.50(1936)48-58 Large electric field across the insulating layer Electrons are ‘pulled out’ from the cathode • Factors which facilitate an ignition: • Poor cathode conductivity • (some oxides are highly resistive, carbon • composite materials may not be conducting • enough - Pokalon-C, HERA-B OTR) • Highly ionizing particles or sparks Once Malter current is persisting it will lead to high local ionization densities and initiate production of new reactive species or produce them at much larger rates thus promoting polymer formation !!! When Malter effect appears apply additives immediately or disconnect ‘damaged detectors’, otherwise it could spread throughout your large system M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  16. Tests with prototype BaBar Drift Chamber Recovery from the cathode aging (Malter effect) with water additive Preaged chamber in He/iC4H10(80:20) with 100 mC Fe55source Start with a damaged chamber - Malter current at very low current Water is the best (run above 10 nA/cm) Strong dependence of Malter effect from current density: N(single pulses)/N(Fe55) No additives N(single pulses)/N(Fe55) Time (s) When the additives are removed, the chamber would suffer from the Malter at a very low current again Time (s) 200-1000 ppm of O2 and CO2 in the presence of high ionization can revert or cure a chamber from Malter breakdown With additives: Methylal, Propanol and H2O provide immediate relief from Malter breakdown (A. Boyarski - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  17. Aging in Large CDF Central Tracking Chambers • Prior to Run1: prototype CTC chamber with Ar/C2H6(50:50) +1% alcohol: R<10%(/C/cm) • In 1995, aging rate R~1000%(/C/cm) in the large CTC detector was observed Wire from test chambers (inserted into CTC gas flow; deposits are dominated by Si,O). • After cleaning the gas system and making changes to reduce aerosols from the • alcohol bubbler, aging was greatly reduced New tests with prototype COT chamber: monitor chambers show R <1% C/cm. (M. Binkley - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  18. Silicon Contamination Silicon contamination is one of the most serious problems for wire chambers Aging tests for ATLAS TRT straws with Xe/CF4/CO2: The balance between Si polymerization and etching is very sensitive to the Si source intensity and the ionisation density(no deposits were observed at currents >1 mA/cm dominating etching property of CF4) For a long time CF4 plasmas have been used to remove Si-based deposits: H2 added to CF4 decreases F/CF2 etching SiO2 O2 added to CF4 increases F/CF2 etching Si (A. Romaniouk, F. Sauli - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  19. Start of Run 1: WAMUS PDT: Ar/CF4/CO2(90:6:4) Wires became very inefficent: Flash cleaning (ZAPPING): (clean 1000’s wires in situ) If the wire is heated quickly(<2 ms) to a temperature close to the melting point of gold, the crud blows away • Sheath of crud covering the sense wires • (Outgassing of Glas-steel polyester- • epoxy resin from cathode pad) • No deposits on cathodes or walls • New wires restore the original gain Zapped crud (blown off sheath) Although all chambers share one recirculating gas system, many are dead, some are half dead and half good, and a few are fine • Crud removal attempts: • Water (no good, cell became • covered with Al2O3) (T. Marshall - Aging Workshop 2001, DESY) Aging studies of Muon Drift Tubes at D0 experiment M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  20. Conclusions: Materials and gases for 'standard' detectors • ‘Moderately’ clean environment and cleaning procedures during detector • construction, use of well-tested ‘good old materials’ • Prior to start of operation, cleaning of the gas mixing and distribution system • Avoid the well-known ‘bad molecules’ in contact with active gas • (Si-oil and rubber, halogens(ex. CF4), plasticizers, phthalats, PVC, epoxy outgassing) If you did something wrong, and are UNLUCKY: Example: Permanent damage due toinappropriate choice of PVC-tubing even for a limited period Huge variety of gases can be used (noble gases, hydrocarbons, CO2, freons, H2O, alcohol, magic gases, …) Hydrocarbons in the operating gas are the most likely source of direct aging (effect is more pronounced under glow discharges, sparks and Malter currents ) Use additives from the very beginning, not when aging effects appeared (B. Schmidt, J. Va’vra - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  21. Choice of Materials and Gases for high-rate detectors of the LHC era (HERA-B, LHC exp. + MSGC community) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  22. Choice of materials for LHC type detectors The amount of pollutantsin thesystem(detector + gas system) plays a major role in determiningthe aging properties; outgassing from materials, epoxies, joints, and tubing has tobe carefully controlled and kept at ppm level or better Consult the NASA database + RD28 experience as a guideline to start with NASA DATABASE - Outgassing Data for selecting Spacecraft Materials http://epims.gsfc.nasa.gov/og/index.cgi (More than 1600 entries for adhesives, 500 entries for rubbers and elastomers, 800 entries for potting materials) RD28: aging results from MSGC community To get information about the effect of pollutants: Gas Analysis + Aging Test (M. Capeans, B. Schmidt - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  23. Low Outgassing Epoxy Compounds (Room temp. curing) Outgassing Tests of Some Materials • Epoxy Compounds • Adhesive Tapes • Leak Sealers • Rigid materials • Poss. Contamination: • - User-generated • - Silicone ‘Rejectable Epoxy Compounds’ (Room temp. curing) Outgassing of Epoxy Compounds • Material itself • User-generated • - Poss. Contamination: • -Incorrect ratio of • hardener to resin • -Insufficient curing time (M. Capeans - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  24. Full evidence of suitability (long-term MSGC aging test) Epoxy Compounds Curing at T > 50 C (in order to increase the sensitivity of the system, samples warmed up) Conductive epoxy Compounds Adhesive Tapes (M. Capeans - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  25. Outgassing Tests of Leak Sealers Full evidence of suitability (long-term MSGC aging test) Rigid Materials (M. Capeans - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  26. User-generated Outgassing NEW vs EXPIRED PU:NUVOVERN LW -HARDNER PUR LW Polyurethane (new batch) Polyurethane (expired) (F. Sauli - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  27. Comparison of NASA, Chromatography and Aging Test results Both used for detector construction Even if outgassing is detected, it might not be harmful for the gaseous detector !!! You have to dotests to match your specific requirements (M. Capeans - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  28. Gas pipes Plastic pipes:PTFE, NYLON,PVC, PU high gas permeability, possible outgassing, cheap Metal pipes:copper, stainless stell 0 gas permeability, 0 outgassing, expensive Outgassing Tests of Plastic Pipes 20 m of Nylon Pipe on the chamber inlet ~ 1700 ppm H20 Extremely dangerous for MSGC, RPC, straws (M. Capeans - Aging Workshop 2000) !!! Take into account possible radiation-induced outgassing (don’t use long supply plastics lines in a high irradiation environment) !!!Add plastics with the greatest care !!! As much steel as possible, as little plastics as possible M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  29. Recent Aging Experience in RPC's Systems Mid’1990: RPC’s were thought to be a robust, economical and proven technology ideally suited to large-area detection systems. Both Belle and BaBar adopted them for their muon systems. M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  30. Aging Experience in Belle RPC High dark currents started to show up almost immediately upon installation in June’1998 (problem was due ~2000 ppm of H2O) Freon + Water + Streamers HF acid The glass surfaces were etched by HF acid which resulted in a creation of emission points, triggering chamber currents and lowering voltage across the gap. Change of polyethylene tubing withcopper (<10 ppm H2O) (drying out of RPC’s was accompanied by drop in the dark current) Solution: STM Picture of Glass Surfaces Good anode Bad anode (D. Marlow - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  31. Aging Experience in BaBar RPC Linseed-oil RPC’s have exhibited serious damage that appeared to be irreparable • The RPC problem is related to the formation of oil droplets under the influence • of high temperature and high currents (increased rate of chemistry) • Current goes through linseed oil (droplets, frame, buttons) and shorts electrodes • If one runs voltage on a fresh linseed oil creates stalagnites (emission points) • The problems with RPC’s are not classical aging effects (unpredictable surface effects) • Treat RPC’s as a delicate devices during production and running phases (D. Piccollo - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  32. Materials: Conclusions from 2001 Workshop Existing data, obtained either from systematic outgassing studies or experience gained with detector, has only preselective character (a list of low-outgassing assembly compounds exists, that includes epoxy compounds, rigid materials, sealants, elastomers,…) There are clearly many ‘bad’ and a lot of ‘usable’ materials A material is adequate or not for aparticular detector type and operating conditions test to match your specific requirements Do not introduce bad components by unadequate assembly procedures (no quality checks, no personnel training, greasy fingers, polluted tools) No spontaneously chosen materials should be installed in the detector or in the gas system at the last moment, before the start of real operation Building of large detector needs a lot of communication and sharing of know-how of all people in the business If you want to test the cleanliness of your gas system: install MSGC in your gas system, if it survives don’t worry (B. Schmidt, M. Capeans, F. Sauli - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  33. Experience with high-rate detectors of the LHC era (HERA-B, LHC + all MSGC community) Charged particle fluxes seen by tracking detectors: M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  34. Aging Studies for the HERA-B Outer Tracker Chamber construction & parameters • Criteria for the gas choice: • Little aging • Drift distance up to 5 mm • Maximum drift time 96 ns Need a fast, CF4-containing gas mixture (V~80-100mm/ns) Mixtures studied: CF4/CH4 (80:20) Ar/CF4/CH4 (74:20:6) Ar/CF4/CO2(65:30:5) Large gas volume (22 m3) expensive gas (CF4) Open honeycomb geometry 1000 individual modules largest superlayer - 4.6*6.5m2 Need a recirculating gas system and purification Total accumulated charge ~ 0.5 C/cm/year M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  35. Aging Studies for the HERA-B Outer Tracker !!!Strong aging dependence on particle type: Chambers with uncoated Pokalon-C cathode: HERA-Bhigh-rate environment: Persistent Malter currentsin full-size prototype honeycomb chambersafter ~ 0.5 mC/cmof accumulated charge X-rays setup: Small area honeycomb chambers had shownno aging effects up to 4.5 C/cmof integrated radiation dose Further R&D to resemble HERA-B conditions: Very fast anode aging observed Hadrons above certain energy produce Malter effect at ~mC/cm as in HERA-B (Irradiation area above certain limit is necessary for ignition of Malter effect) X-rays or e- can not trigger Malter effect independently of their energy or radiation intensity (C. Padilla, - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  36. Aging Studies for the HERA-B Outer Tracker Intense R&D program: All building materials (glues, plastics, wires) and technique were tested and validated Solutions: Problems observed: • Coat 1200 foils with 40 nm Cu • (good adhesion to plastics)+ • 40 nm Au (gas contact) • Indications that the foil is • responsible for Malter effect • (related to conductivity) • New glue (Stycast) • Araldit • Fast anode aging is due to • Ar/CF4/CH4 • Change to Ar/CF4/CO2 Stable gain for more than 2 HERA-B years (~ 1C/cm) Chamber would not operate in HERA-B longer than 10 hours BUT, with Ar/CF4/CO2 (65:30:5) Operation is possible, if 50 ppm < H2O < 500 ppm Carefully control thewater content (100-500 ppm) of the gas ! Dark current (FR4 strips become conductive) Wire etching (gold peels off) (C. Padilla, - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  37. Similar to Plasma Polymerization... Plasma chemistry: CF4 can be used for both etching and deposition processes the distinction mainly due to the CF4concentration Etching: addition of oxygenated species Deposition: addition of hydrogenated species Wire Chambers: HERA-B OTR honeycomb chambers which were initially aged with Ar/CF4/CH4, were recovered after replacing CH4 withCO2 I(irrad)/I(refer) Current density ~0.8 mA/cm (M. Capeans - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  38. Aging Studies for the HERA-B Muon Detector Aging Tests in a 100 MeV a-beam (8 * 8 cm2) Chamber construction: 45 mm Au-plated W Ar/CF4/CH4(74:20:6) Gain reduction observed after 60 mC/cm (R~800%) Aging Tests with Fe55 and Ru106 sources Total collected charge 280 mC/cm: Wire irradiated over half of their cell width ? ? Fe55 source R ~ 8 % HERA-B environment 100 MeV a’s R ~ 800 % (M. Titov - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  39. Aging Studies for the HERA-B Muon Detector HERA-B high-rate environment (size of irradiation area ~1500 cm2): Ar/CF4/CH4 (67:30:3) + 500 ppm H2O Gain reduction and dark currents for wires operated at gain >105 appeared at 25 mC/cm: Progressive deterioration of performance in the direction of the serial gas flow CF4+CH4 aging: Wire deposits, containing only C and F (H is not observable) High voltage Area of irradiation Strong dependence of aging rate on: (M. Titov - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  40. Aging Studies for ATLAS Muon Detector (MDT) X-ray irradiation, Ar/CH4/N2/CO2 (94:3:2:1) Strong dependence of the tube lifetime on: • High Voltage Total charge of the avalanche Gas gain • Irradiation rate • Concentration of reactive species • Area of irradiation • If long-lived species are produced • in the avalanche the aging effects • became non-local and • intensity dependent (M. Kollefrath- Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  41. Some conclusions: Description of aging rate by a single parameter: R=-1/G(dG/dQ) is not adequate Initial stage of radiation tests usually performed in the laboratory may not offer full information, needed to give an estimation about the lifetime of the real detector Clear evidence for aging dependence on: aging as non-local phenomena • irradiation rate • ionization density • high voltage (gas gain) • particle type and energy • gas exchange rate • size of irradiated area Effect of microdischarges & Malter currents: increase in polymer production rate or production of new reactive species The aging performance not only depends on the chemical nature of the mixture, but also on the actual discharge conditions M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  42. Aging properties with Ar/CF4/CO2: • Little gain losses have been observed in clean setups, BUT !!! • Some evidence of gold etching and wire surface damage (cracks) • Accumulation of fluorocarbon deposits on the cathodes Aging studies in Ar/CF4/CO2 HERA-B MUON DETECTOR: Ar/CF4/CO2 (65:30:5)+1000 ppm H2O HERA-B OUTER TRACKER: Ar/CF4/CO2 (65:30:5)+ 20-500 ppm H2O No loss in performance up to ~0.7 C/cm, with 5 different gas gains (from 104to 3*105) No loss in performance up to ~3 C/cm, after 3000 hours of operation in aging test LHCB full scale MWPC prototype: Ar/CF4/CO2 (40:50:10) No significant deterioration of chamber performance up to ~0.25 C/cm CMS Cathode Strip Chamber: Ar/CF4/CO2(30:50:20) & Ar/CF4/CO2 (40:50:10) • No gain reduction in prototype chambers up to 13.5 C/cm, fast rate of accum. 0.3C/day • No significant changes in large area chamber performance up to 0.4 C/cm. M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  43. Gold damage effects on the wires WO deposit Xe/CF4/CO2 (70:20:10) Straws for ATLAS TRT: • Current density ~5mA/cm • Gold etching processes • appear for different accum. • charges (0.5 - 6 C/cm) • No F-based deposits • have been observed (A. Romaniouk - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  44. Gold damage effects on the wires Xe/CF4/CO2 (70:20:10) Straws for ATLAS TRT: current density ~5 mA/cm Possible reasons of gold damage: • Main components responsible for wire damage are reactive species • produced in CF4 avalanches (probably HF acid) • Presence of oxygen speeds up wire damage (WO deposit) • No gold damage effects observed for H2O concentrations below 0.1% • with Xe/CF4/CO2 mixture up to 20 C/cm • Effect depends on type of wire (producer and production technology) (A. Romaniouk - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  45. Anode wire swelling phenomena Straws with Ar/CO2/C2H2F4 (40:40:20), Q ~ 1.6 C/cm Current density ~ 3 mA/cm X=-14 cm X=0 cm X=+14 cm • Anode wire deposits were found 13 cm downstreamfrom the irradiated area • Wire swelling effect was also observed with Xe/CF4/CO2(70:20:10) after 9 C/cm • (gold coating was broken and wire diameter increased from 35 mm to 42 mm) (A. Krivchitch - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  46. Production of the long-lived electronegative species • is it possible to remove them with purification system? • Effects of the highly reactive CFx and F radicals (produced in CF4 • gaseous discharges) on the detector materials and electrode surfaces • Progressive deterioration of performance along the gas flow • in Ar/CF4/CH4 mixtures Will large systems with CF4-containing mixtures work? Electronegative radical production in straws with Xe/CF4/CO2 (50:20:30) Proportional counter response placed downstream the irradiated straw Significant suppression of pulse-height when straw tube irradiation is turned on Large detectors, gas recirculation systems and CF4- Open questions: (F. Sauli - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  47. Large System Aspects: aging rate vs current density High intensity experiments (high current densities over the large areas) Laboratoty: accelerated aging tests (~cm wire) => Need tests of full scale detectors in high-rate environments: Aging is non-local phenomena (progressive deterioration of performance along the gas flow) Any imperfections could trigger discharges, Malter currents - polymerization guaranteed Large system aspects: extra high quality of electrode surfaces & cleanlinness of the gas systems (~20 m3) are hardly reachable The counting gas under discharges is a much better conductor that many insulators (M. Capeans, F. Sauli, J. Va’vra - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  48. 'Aging' in MSGC Detectors MSGC are more susceptible to aging than MWPC Major processes leading to degradation of performance of MSGC: substrate charging up, surface deposition of polymer, microdischarges Use of MSGC based on: • Electron-conductive glass • ‘Diamond-like coating’ of the glass • (no gain reduction up to 80 mC/cm • irradiating with X-rays, 10 HERA-B years) • Borosilicate glass results in rate-dependent • modification of gain due to a radiation • induced variation of surface resistivity NO disharges with X-rays and electrons Discharges with a-source and in HERA-B (discharge rate ~ many per min) Induced discharges are intrinsic problem of the MSGC principle (=> no gains >2000 in hadronic beams) Two-stage multiplication is necessary MSGC+GEM combination (F.Sauli) (M. Hildebrandt - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  49. MSGC-GEM Detector for HERA-B Inner Tracker System The Gas Electron Multiplier as a Charge Amplification Stage Chamber construction and parameters Diamond coating Choice of the operating gas: • To prevent fast aging at high rates, • avoid the use of hydrocarbons • Mixtures studied: Ar/CO2,Ar/DME,Ar/CF4/CO2 • The diamond coating is etched away • almost completely near the anode in : • Ar/CO2 after 40 mC/cm (5 HERA-B years) • Ar/CF4/CO2 after 2 mC/cm • Ar/DME is better quencher than Ar/CO2 (M. Hildebrandt - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

  50. Aging of MSGC-GEM Detectors HERA-B Inner Tracker with Ar/DME(50:50) • Aging effects strongly depend on the size of irradiated area • Neither dirty gas system nor simple outgassing (no indication from GC) • Polymerization of DME itself or pollutants ? • Use of DME in Wire Chambers: • Reasonably good radiation hardness of DME is reported • Aging rate of DME is highly sensitive to traces of pollutants • Evidence of DME damaging materials (V.Blinov, R. Henderson, F. Sauli - Aging Workshop 2001, DESY) M.Hohlmann (FIT) -- Workshop Summary: "Aging Phenomena in Gaseous Detectors" (DESY '01)

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