Mar Capeans CERN. Invited review talk at the International Workshop on Aging Phenomena in Gaseous Detectors

Transcription

1 and gases: Lessons for detectors and gas systems Mar Capeans CERN Invited review talk at the International Workshop on Aging Phenomena in Gaseous Detectors M. Capeans 1

2 Outline Ageing Outgassing studies Detector Assembly Detector Assembly Components for Gas Systems Influence of Some on Ageing M. Capeans 2

3 The Very Basic Knowledge Gaseous detectors operated in a high radiation environment can have serious operational problems due to ageing. Commonly ageing manifests as: Loss of gas gain Worsening of energy resolution Excessive currents Selfsustained discharges Sparking All these are usually related to the presence of deposits coating the electrodes (anode and/or cathode). M. Capeans 3

4 Basic Knowledge The ageing process is due to very complex phenomena that take place during the gas avalanche (~ plasma chemistry). These phenomena lead to the creation of a wide variety of species that may accumulate as deposits, conductive or insulating, on the electrode surfaces. Polymerization Polymers Solid, highly branched and cross linked Excellent adhesion to surfaces Resistant to most chemicals Insoluble in most solvents M. Capeans 4

5 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 Nature of gas Traces of contaminants Experimental observations are difficult to compare and/or extrapolate between one another. M. Capeans 5

6 1986 US Recent experience SDC Straw tubes, Pad chambers, CERN Basic R&D MSGC community Detector R&D for LHC HeraB construction DELPHI, RD10, RD28, RD6, RD28, HeraB, CMS, ATLAS, ATLASTRT, ATLASMDT, CMS CSC, OTR, ITR, Muons Still comparison and/or extrapolation is difficult but all this experience provides a solid basis for discussion M. Capeans 6

7 Contributions to the Ageing Process Polymerizing Mixtures Uncontrolled Pollution (gas cylinders) Pollutant Outgassing GAS Reactive/Solvent MATERIALS Reactive Avalanche Products Radiation (structural changes) M. Capeans 7

8 Outgassing Tests of Some Outgassing studies Epoxy compounds Adhesive tapes Leak Sealers Rigid Contamination Methods Low outgassing, Room T curing Rejectable, Room T curing Curing at T > 40 co Conductive Usergenerated Silicone M. Capeans 8

9 Gas analysis of a sample Gas in PRESELECTIVE CHARACTER The Minimal SetUp Outgassing Box Analysis Station Impurity detection has the intrinsic limitations of the analysis station, 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 the gaseous detector. M. Capeans 9

10 Gas Chromatography Basics Gas in Carrier Gas GC ECD MSD GC: oven with a capillary column. Function: it separates gas substances depending on their interaction properties with the column. Signal: a signal appears for each separated compound at some retention time, defined by the column and temperature profile. MSD: 70 ev e source to ionize and fragment molecules + quadrupole mass filter to sort resulting ions according to their M/Z ratio. Function: it identifies each molecular compound. Signal: ion abundance as function of retention time in the column or M/Z ratio. Sensitivity: ~ ppm ECD: βe bombard a carrier gas to form a plasma. Thermal e are collected applying an Efield. The decrease of the detector current due to removal of thermal e by recombination in presence of electrocapturing compounds gives a signal. Function: detection of electronegative substances Signal: signal amplitude vs. time. Sensitivity: ~ ppb M. Capeans 10

11 Gas Chromatography Basics Selection of column, temperature profile and carrier gas nature and flow defines the sensitivity of the station. MSD signal 10 ppm F12+F11 ECD signal 10 ppm F12+F11 M. Capeans 11

12 Gas Analysis + Detector irradiation To get information about the effect of pollutants: Gas Analysis + Ageing Test Clean Gas detector (full metal SWPC or any other validated device) Small prototype of final detector Gas in Outgassing Box Gaseous Detectors Analysis Station Limitations: Irradiation conditions (high dose rates) Time scale (~months) M. Capeans 12

13 TML & CVCM Method Developed at NASA to search low outgassing materials for spacecraft use. PRESELECTIVE CHARACTER Test of conditioned microquantities in vacuum at stated temperatures and specific times. Technique of condensing the volatile products to determine the amount of volatile condensable materials. Output: Low Outgassing Material TLM < 1% & CVCM < 0.1% % TML = Total Mass Loss It is determined from the weights before and after the temperature exposure. % CVCM = Collected Volatile Condensable It is the difference between the weight of a clean collector and of the collector having condensed materials. M. Capeans 13

14 Epoxy Compounds Parameters to take into account during selection: Shear strength Elongation at break Viscosity Electrical properties Capillary effect Radiation resistance Outgassing Material itself Usergenerated (hard to trace): Pollution Incorrect ratio of hardener to resin Insufficient mixing Insufficient curing time M. Capeans 14

15 Low Outgassing Epoxy Compounds RoomT Curing Source Product Outgas Effect in G.D. Note STYCAST 1266 (A+B) Long curing time HERAB/OTR STYCAST 1266 (A+Catalyst 9) In Use HEXCEL EPO 93L Out of production HERAB/ITR ECCOBOND 285 In Use ATLAS/TRT ARALDITE AW103 (Hardener HY 991) In Use ATLAS/TRT TRABOND 2115 In Use M. Capeans 15

16 Rejectable Epoxy Compounds RoomT Curing Source Product Outgas Effect in G.D. Result ATLAS/TRT ARALDITE AW 106 (Hardener HV 935 U) DURALCO 4525 DURALCO 4461 HEXCEL A40 TECHNICOLL (Hardener 8263) RLAND NEA 155 EPOTEK E905 RLAND NEA 123 (UV) M. Capeans 16

17 TESTS OF ARALDITE AW 106 (+HV953U) AGEING TEST GC+MSD hexane trimethyl pentane trimethyl butane xylene butane NASA TEST TML 3.26% CVCM 0.02% M. Capeans 17 Ion Current (A) ION Analyzer H 2 O C. Bellachioma, E.Broilo, P. Chiggiato, M. Van Stenis CERN CO O 2 CO 2 Araldite 103_2 Araldite Mass

18 Epoxy Compounds Curing at T > 50 o C Source Product Curing T ( o C) Outgas Effect in G.D. Result EPOTECNY E505 SIT 50 HERAB/ITR EPOTEK H72 65 * * AMICON POLYIMIDE DUPONT ATLAS/TRT RUTAPOX L20 60 ARALDITE AW LOCTITE 330 EPOTECNY (Silicone) RLAND UVS M. Capeans 18

19 Conductive Epoxy Compounds Source Name Outgas Effect in G.D. Result TRADUCT 2922 HERAB/OTR SILBER LEITKLEBER 3025 (A+B) ATLAS/TRT TRABOND 2902 Adhesive Tapes Source Name Outgas Effect in G.D. Result HERAB/OTR SCOTCH 467 MP HERAB/OTR TESAFIX 4388 M. Capeans 19

20 Outgassing Tests of Leak Sealers Source Material Type Outgas Effect in G.D Global Result VARIAN TorrSeal Solventfree epoxy resin RHODORSIL CAF4 Caoutchouc Silicone RTV in very small quantities? DOW CORNING R43117 RTV Silicone based in very small quantities? HERAB /OTR LOCTITE 5220 Polyurethanebased M. Capeans 20

21 Rigid Source Name Type Outgas Effect in G.D. Result STESALIT 4411W Fiberglass VECTRA 150 Liquid Crystal Polymer PEEK Crystalline Polyeteherether ketone ATLAS/TRT ULTEM Polyetherimide ATLAS/TRT CFiber Cfiber ATLAS/TRT POLYCARBONATE Cfiber HERAB/ITR FIBROLUX G10 Fiberglass HERAB/ITR HGW 2372 EPGF Fiberglass RYTON Polysulphur phenylene PEEK Amorphous Polyetherether ketone M. Capeans 21

22 Usergenerated Outgassing 2component Polyurethane (Nuvovern LW) Ion Current (A) 10 9 PU Adequate processing PU 1 component expired H O 2 C H C H 3 8 OH 2 6 CO CO 2 O 2 C.Bellachioma, E.Broilo, P.Chiggiato, M.V.Stenis CERN Mass 100 M. Capeans 22

23 Comparison CVCM, Chromatography, Ageing Test SAMPLE NASA GC Ageing test Stycast 1266 Araldite 103 Araldite 106 Eccobond 285 Nuvovern LW PUR ULTEM VECTRA 150 Kalrez Epotek 905 Dow Corning RTV Consult NASA database to select materials, before doing the timeconsuming tests NASA Database: More than 1600 entries for adhesives, 500 entries for rubbers and elastomers, 800 entries for potting compounds, etc M. Capeans 23

24 Silicone Contamination Silicone has been systematically found coating aged chambers. 3 Silicone has a high natural affinity for most materials. Silicone has the tendency to migrate. Silicone is relatively inert chemically and unaffected by most solvents, therefore among the most difficult surface contaminants to remove. Silicone is etched away by F species. 3 Possible Sources: Silicone rubber sealants Silicone potting and encapsulation compounds Silicone adhesives Silicone Vacuum Grease (Orings, mouldrelease agents) Silicone oil (bubblers, diffusion pumps) Polluted gas cylinders Detergent residues (sodium metasilicate) Glass and related products (glass fibres used for reinforcing resins) M. Capeans 24

25 Accidental Silicone Contamination ATLAS/TRT ATLAS/TRT S. S. Mouraviev Mouraviev CERN CERN Wheel 2, straw p96g1c06 after 14 hours irradiation E Resolution Weak 55 Fe ~ 700 Hz Mean Amplitude Amplitude ~ 10 % gain loss D M M D D R, cm M. Capeans 25

26 Silicone Contamination Si deposit Si deposit Clean wire Irradiated spot Region between two irradiated spots Silicone Source: Siliconebased lubricant used accidentally during straw tube manufacturing by the manufacturer. Mass production straws are free of pollution (no lubricant at all). M. Capeans 26

27 Silicone Contamination: Sibubbler GDD GDD Group Group CERN CERN MSGC in clean gas system Add Siliconoil bubbler to chamber exhaust M. Capeans 27