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Malte Hildebrandt

Detailed discussion on hardware status and performance tests of the Drift Chamber System. Highlights installation changes and DC target optimizations in comparison to the previous year. Insights on HV modules, performance issues, and system shutdown activities.

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Malte Hildebrandt

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  1. Drift Chamber System • hardware status Run 2008 • shutdown activities 2009 MEG Review Meeting Feb 2009 Malte Hildebrandt Malte Hildebrandt MEG Review Meeting, 18.02.2009

  2. Outline • installation 2008 • MEG Run 2008: • characteristics of HV instabilities • tests with dc system in MEG • tests in laboratory • Shutdown • preparations, tests • first test results • Summary / Outlook Malte Hildebrandt MEG Review Meeting, 18.02.2009

  3. Installation 2008 • main changes/improvements in 2008 compared to installation in 2007: → topics were already noted in last years DC Status Talk at the Review Meeting as „needs to be done“ / „ will be improved“) • improved strain-relief of LV and signal cables at inside patch panel → no disconnected LV cable 2007: LV dc6u disconnected → 13 missing signal channels 2007: 42 missing connections ↔ crucial step during installation: closing end-cap • more detailed analysis of optical survey of dc system → geometrical alignment includes slope of wires along z-axis 2007: wire at constant x and y, parallel to z-axis (UCI group startet to implement slope) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  4. Installation 2008 • main changes/improvements in 2008 compared to installation in 2007: → topics were already noted in last years DC Status Talk at the Review Meeting as „needs to be done“ / „ will be improved“) • optimised target → new support spacers and 2007: target slightly misaligned new attachment screw-plate to correct position in space → slant angle adjusted to (20.5 ± 0.3)° 2007: (12.8 ± 0.5)° Malte Hildebrandt MEG Review Meeting, 18.02.2009

  5. Target 2008 2007 Malte Hildebrandt MEG Review Meeting, 18.02.2009

  6. Installation 2008 • main changes/improvements in 2008 compared to installation in 2007: → topics were already noted in last years DC Status Talk at the Review Meeting as „needs to be done“ / „ will be improved“) • optimised target → new support spacers and 2007: target slightly misaligned new attachment screw-plate to correct position in space → slant angle adjusted to (20.5 ± 0.3)° 2007: (12.8 ± 0.5)° → identification marks on target Malte Hildebrandt MEG Review Meeting, 18.02.2009

  7. Installation 2008 • main changes/improvements in 2008 compared to installation in 2007: → topics were already noted in last years DC Status Talk at the Review Meeting as „needs to be done“ / „ will be improved“) • optimised target → new support spacers and 2007: target slightly misaligned new attachment screw-plate to correct position in space → slant angle adjusted to (20.5 ± 0.3)° 2007: (12.8 ± 0.5)° → identification marks on target → measurements of inclination: • conventional (sliding rule) 2007(2008): conventional • photogrammetric 2007: photogrammetric • optical survey Malte Hildebrandt MEG Review Meeting, 18.02.2009

  8. New DC HV Modules ↔ S.Ritt ↔ R.Schmidt • during Run 2008: modification of dc HV modules • observation (in 2007, June - July 2008): • several times “blocking” / “freezing” of complete communication: MSCB Submaster, HV nodes, LabView • in combination with HV trips of several HV modules but: cause and effect not clear… → new HV modules: • watchdog: reboot of mController in case of missing toggle signal from mController (→ HV off) • new bus driver: „state machine“ decouples from the bus when not transmitting data → no blocking of bus line with „active high signal“ in case mController stucks • smaller capacitance at HV_output reduces trip propagation within HV module • geographical addressing of nodes within crates Malte Hildebrandt MEG Review Meeting, 18.02.2009

  9. HV Performance • summary: • many dc planes / modules suffered from frequent HV trips • consequently theses planes / modules could only be operated with reduced HV settings → huge impact on overall performance of dc system (→ talk by B.Molzon) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  10. HV Performance • summary: • many dc planes / modules suffered from frequent HV trips • consequently theses planes / modules could only be operated with reduced HV settings → huge impact on overall performance of dc system (→ talk by B.Molzon) • phase 1: June – July • 30 / 32 planes >1800 V(remark: nominal 1850 V) m beam • 2 planes showed problems right from beginning • phase 2: Aug • dc system most of the time off, short period on p beam • 19 / 32 planes >1800 V • 6 / 32 planes 1700-1800 V • phase 3 : Sep – Dec • further deterioration of HV performance m beam • 11 / 32 planes >1800 V • 7 / 32 planes 1700-1800 V Malte Hildebrandt MEG Review Meeting, 18.02.2009

  11. Phase 1 • phase 1: June – July • m beam, start-up phase, e.g. HV ramping • 2 dc planes showed problems right from beginning • dc10A: always <1300-1500 V • dc03A: once 1850 V, then setback down to 1300 V, recovery within weeks up to 1700 V • all other planes: air admixture to COBRA gas (outside module) necessary to achieve stable dc operation → cHelium ≈ 95-96 % (reading O2 sensors) (instead of „pure“ helium level around 99.0-99.5 %) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  12. Air Admixture Sat, 19.07., 02:00 32ccm / 2000ccm (1.60%) cHelium=99% ~96-97 % ~95-96 % ~95-96 % ~94-95 % cHelium=95% cHe= ~93 % Wed, 16.07., 12:40 24ccm / 2000ccm (1.20 %) Mon, 30.06., 08:15 30ccm / 2000ccm (1.5 %) Tue, 01.07., 08:45 55ccm / 2000ccm (2.75 %) Sun, 06.07., 23:00 40ccm / 2000ccm (2.00 %) Sat, 12.07., 15:00 32ccm / 2000ccm (1.60 %) Mon, 30.06., 17:45 65ccm / 2000ccm (3.25 %) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  13. Phase 1 • phase 1: June – July • m beam, start-up phase, e.g. HV ramping • 2 dc planes showed problems right from beginning • dc10A: always <1300-1500 V • dc03A: once 1850 V, then setback down to 1300 V, recovery within weeks up to 1700 V • all other planes: air admixture to COBRA gas (outside module) necessary to achieve stable dc operation → cHelium ≈ 95-96 % (reading O2 sensors) (instead of „pure“ helium level around 99.0-99.5 %) → end of July: 30 / 32 planes operational with >1800V (remark: nominal 1850 V) • occasional problems with communication of HV modules / MSCB / LabView → modify HV modules during XEC run Malte Hildebrandt MEG Review Meeting, 18.02.2009

  14. Phase 2 • phase 2: August • p beam, XEC run, Dalitz run • XEC run: • dc gas system running continuously • dc HV system off for 2½ weeks (modifications of HV modules) • 10 days dc HV at 800-1000 V • Dalitz run (e+ e- identification in Dalitz decay p0 → e+ e-g) • 5 days dc HV on nominal values → current load/plane: 0.7-1.0 mA (compared to 10-12 mA with m beam) • but: many HV trips, number of „weak“ planes increased → beginning of September: • 19 / 32 planes >1800 V • 6 / 32 planes 1700-1800 V Malte Hildebrandt MEG Review Meeting, 18.02.2009

  15. Phase 3 • phase 3: September – December • m beam: MEG physics run • several tests with running system: • to understand reason of HV trips → see separate transparency • to possibly stop or even recover deterioration • but still: many HV trips, number of „weak“ planes increased further → end of December: • 11 / 32 planes >1800 V • 7 / 32 planes 1700-1800 V • in parallel: new test setup in laboratory (HV pcb, potting of capacitors, HV) → see separate transparency Malte Hildebrandt MEG Review Meeting, 18.02.2009

  16. HV Trips • characteristics of HV trips: • individual „treshold effect“ for affected planes • deterioration due to frequent trips (due to damage?) • no obvious correlation with beam off/on, magnetic field off/on or muon target/CW target tube ↔ exception for 2-3 planes: • beginning of run period: HV trip while beam blocker opened → improved during run time („training“ ?) • during run period: HV trip 10-20 min after beam blocker closed Malte Hildebrandt MEG Review Meeting, 18.02.2009

  17. HV Trips • characteristics of HV trips: • beginning of run period: air admixture to COBRA gas necessary to achieve stable dc operation → cHelium ≈ 95-96 % • significant deterioration started after: • p beam time (XEC, Dalitz) • 2-3 months with dc + COBRA gas and HV → at beginning: same planes affected as in 2007 • further deterioration due to frequent HV trips during remaining run time (2008: May – Dec) even without any further p beam time • stable operation (with reduced HV settings) during second p beam time (5 days) 2007: cHelium ≈ 96 % 2007:p at end of run 2007: after 2-3 months with gas and HV 2007: similar, but: shorter run time (Sep – Dec) 2007: dc system off during p beam time Malte Hildebrandt MEG Review Meeting, 18.02.2009

  18. HV Trips • characteristics of HV trips: • beginning of run period: air admixture to COBRA gas necessary to achieve stable dc operation → cHelium ≈ 95-96 % • significant deterioration started after: • p beam time (XEC, Dalitz) • 2-3 months with dc + COBRA gas and HV → at beginning: same planes affected as in 2007 • further deterioration due to frequent HV trips during remaining run time (2008: May – Dec) even without any further p beam time • stable operation (with reduced HV settings) during second p beam time (5 days) 2007: cHelium ≈ 96 % 2007:p at end of run 2007: after 2-3 months with gas and HV 2007: similar, but: shorter run time (Sep – Dec) 2007: dc system off during p beam time → deterioration due to p beam time ? Malte Hildebrandt MEG Review Meeting, 18.02.2009

  19. HV Trips • characteristics of HV trips: • beginning of run period: air admixture to COBRA gas necessary to achieve stable dc operation → cHelium ≈ 95-96 % • significant deterioration started after: • p beam time (XEC, Dalitz) • 2-3 months with dc + COBRA gas and HV → at beginning: same planes affected as in 2007 • further deterioration due to frequent HV trips during remaining run time (2008: May – Dec) even without any further p beam time • stable operation (with reduced HV settings) during second p beam time (5 days) 2007: cHelium ≈ 96 % 2007:p at end of run 2007: after 2-3 months with gas and HV 2007: similar, but: shorter run time (Sep – Dec) 2007: dc system off during p beam time → deterioration due to p beam time ? → deterioration due to helium environment ? Malte Hildebrandt MEG Review Meeting, 18.02.2009

  20. Tests during MEG Run • infrastructure / hardware: • independent Bertan HV power supplies • HV cables • trip test with oscilloscope (MEG and lab) → no improvement • variation of dp_dc regulation value (pdc-pCOBRA): • ↔ small leaks ? Malte Hildebrandt MEG Review Meeting, 18.02.2009

  21. Location of HV Problems • HV problems at top of U-branches: systematics or just by chance? 15th Oct 2008 → due to difference in ρof He and He/C2H6: • dc operation at slightly lower dp_dc level of dp_dc measurement dp • dc operation at slightly higher dp_dc Malte Hildebrandt MEG Review Meeting, 18.02.2009

  22. Location of HV Problems • HV problems at top of U-branches: systematics or just by chance? 15th Oct 2008 → due to difference in ρof He and He/C2H6: • dc operation at slightly lower dp_dc level of dp_dc measurement dp • dc operation at slightly higher dp_dc Malte Hildebrandt MEG Review Meeting, 18.02.2009

  23. Tests during MEG Run • infrastructure / hardware: • independent Bertan HV power supplies • HV cables • trip test with oscilloscope (MEG and lab) → no improvement • variation of dp_dc regulation value (pdc-pCOBRA): • ↔ small leaks ? • 0.2 Pa → 2.0 Pa → -10% current/plane due to breathing of dc modules → no improvement • increase ethane fraction in dc counting gas: • ↔ inside sensitive volume ? • He/C2H6: 50/50 → 45/55 → reduction of gas gain by nearly factor 2 → no improvement Malte Hildebrandt MEG Review Meeting, 18.02.2009

  24. Tests during MEG Run • increase air admixture to COBRA: • ↔ outside dc module • phase 1: cHelium ≈ 95-96% • cHelium ≈ 95-96% → ~40% → 0 % → only test that showed effect → but not that clear result as expected for obvious problem „outside of dc module“ → summary of tests with dc system during MEG run period: • no clear cause and effect • but: hint, that problem is connected to longterm exposure to helium (inside and/or outside of dc module) and - at least in some cases - is located outside of dc module! → ensure helium atmosphere during christmas holidays and shutdown → see separate transparency Malte Hildebrandt MEG Review Meeting, 18.02.2009

  25. Tests in Laboratory • check of common aspects of construction/assemby • sequence of production and assemby → no hint from logbook • wire tension → no hint from logbook • HV pcb • sealing/potting of capacitors • sealing/potting of HV soldering spot 2007: several times weak point → new test setup: • HV test setup • pcb, potting material • helium environment • T ≈ 40-45° C • longterm test (>3 months) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  26. HV Test Setup in Lab → new test setup: • HV test setup • pcb, potting material • helium environment • T ≈ 40-45°C • longterm test (>3 months) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  27. HV Test Setup in Lab • 6 test samples: • 2 samples concentrating on sealing of HV cable, no resistors, no capacitors (Fri, Nov 7th) • 2 samples with HV cable, resistors, capacitors (Fri, Nov 7th, Thu, Nov 13th) • 1 sample with pcb_left and pcb_right (Thu, Nov 13th) • 1 sample: pcb glued on Cu-plate (Thu, Nov 20th) • all tested in air at 2kV • status test: • cHelium > 99% (reading of three O2 sensors) • all HVs at 1990V • T = 40-45°C (since Mon, Nov 24th) → update 17.02.2009: • no significant deterioration (still 2kV) → no conclusion for “aquarium” test (“aquarium” = dc test setup in laboratory during shutdown) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  28. 2nd Pressure Control System • construction of 2nd pressure control system for laboratory → operate „aquarium“ independently from MEG pressure control system reminder: • „aquarium“: • setup to operate two dc modules with He/C2H6 as counting gas • within helium atmosphere Malte Hildebrandt MEG Review Meeting, 18.02.2009

  29. Helium Cabin → ensures helium environment for dc system during „waiting time“ in lab → cHelium ≈ 95% (conditions like in COBRA) • closed volume (V = 5.7m3) • windows / frames removable → access to dc modules • operated with the MEG pcs • helium sensor in exhaust line of helium cabin (instead of dc exhaust line) • patch panel is interface/accessible → dc system can be operated like in COBRA Malte Hildebrandt MEG Review Meeting, 18.02.2009

  30. Test Tesults → first results from dc module tests in laboratory • weak point: potting of HV soldering spot on pcb Malte Hildebrandt MEG Review Meeting, 18.02.2009

  31. HV Connection → weak point: potting of HV soldering spot on pcb hood readout hood Vernier pattern anode decoupling capacitors pre-amplifier cards HV connection to pcb + sealing Malte Hildebrandt MEG Review Meeting, 18.02.2009

  32. HV Sealing → nominal condition cable isolation dielectricum potting pcb HV line braided shield → observation after run period several pottings show: • change of shape („flowed away“) • change of color (white → brown) • same observation in 2007/8 (badly applied? no!) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  33. HV Soldering Spot Malte Hildebrandt MEG Review Meeting, 18.02.2009

  34. Test Tesults → first results from dc module tests in laboratory • weak point: potting of HV soldering spot on pcb → replace ThreeBond 1530 with epoxy EPO-TEK 302-3M Malte Hildebrandt MEG Review Meeting, 18.02.2009

  35. Test Tesults → first results from dc module tests in laboratory • weak point: potting of HV soldering spot on pcb → replace ThreeBond 1530 with epoxy EPO-TEK 302-3M • „circumstantial evidence lawsuit“ (no glow by eye, IR camera, ...): • signals on oscilloscope: positive anode signals negative cathode signals • change of gas mixture: no effect (or long delay) → discharge between anode channel and GND but: not towards cathode strip and not in sensitive volume maybe towards frame at the edge or on pcb itself → open dc module to verify or falsify: • wires and cathode foil fine • edges of isolators fine → closer look at vias on pcb Malte Hildebrandt MEG Review Meeting, 18.02.2009

  36. HV Via top layer GND +HV bottom layer 7 mm Malte Hildebrandt MEG Review Meeting, 18.02.2009

  37. dc01A glue no glue no glue Malte Hildebrandt MEG Review Meeting, 18.02.2009

  38. He / C2H6 He air glue glue glue G10 isolator glue G10 isolator glue carbon frame PCB Cross Section bottom layer top layer pcb pcb bottom layer +HV +HV GND Malte Hildebrandt MEG Review Meeting, 18.02.2009

  39. PCB Cross Section d pcb pcb +HV +HV GND glue glue glue G10 isolator glue G10 isolator glue carbon frame Malte Hildebrandt MEG Review Meeting, 18.02.2009

  40. PCB Cross Section d pcb pcb +HV +HV GND glue glue glue G10 isolator glue G10 isolator glue carbon frame Malte Hildebrandt MEG Review Meeting, 18.02.2009

  41. PCB Cross Section d pcb pcb +HV +HV GND glue glue glue G10 isolator glue G10 isolator glue carbon frame Malte Hildebrandt MEG Review Meeting, 18.02.2009

  42. PCB Cross Section pcb pcb +HV +HV GND glue glue glue G10 isolator glue G10 isolator glue carbon frame Malte Hildebrandt MEG Review Meeting, 18.02.2009

  43. Depth of HV Vias dc01A → example: depth of HV via on dc01A upstream downstream a0 0.73 ± 0.03 0.76 a1 0.47 0.80 a2 0.39 0.66 a3 0.14 0.83 a4 0.65 0.67 a5 0.57 0.46 a6 0.64 0.61 a7 0.00 0.47 a8 0.57 0.57 ddesign = 0.80 ± 0.02 location of discharge (identified by signals) remark: all numbers in mm Malte Hildebrandt MEG Review Meeting, 18.02.2009

  44. PCB Cross Section He / C2H6 pcb pcb +HV +HV GND glue glue G10 isolator glue G10 isolator glue carbon frame Malte Hildebrandt MEG Review Meeting, 18.02.2009

  45. Next Steps → following activities will start immediately and run in parallel: motto:confirm„viahypothesis“,startnewconstruction/repairworktoproofsolution • operate „dc skeleton“ (2 anodes + middle cathode) in „aquarium“ → no hood cathode: observe discharge ? • prepare new sample for HV test box: • no glue on ring of via • glue only on ring of via • fill via completely with glue → confirm effect of different „via/glue conditions“ • start construction of anode frames with new pcb design Malte Hildebrandt MEG Review Meeting, 18.02.2009

  46. HV Print 2009 pads for resistors HV print 2009 • traces for HV on middle layer → no HV traces on bottom layer → individual layers with „only HV“ or „only GND“ (3-layer → 4-layer pcb) • „blind vias“ → vias have only necessary depth to connect appropiate layers (like „blind hole“) print 2007 outer edge inner edge +HV traces vias for +HV GND print 2009 Malte Hildebrandt MEG Review Meeting, 18.02.2009

  47. Next Steps → following activities will start immediately and run in parallel: motto:confirm„viahypothesis“,startnewconstruction/repairworktoproofsolution • operate „dc skeleton“ (2 anodes + middle cathode) in „aquarium“ → no hood cathode: observe discharge ? • prepare new sample for HV test box: • no glue on ring of via • glue only on ring of via • fill via completely with glue → confirm effect of different „via/glue conditions“ • start construction of anode frames with new pcb design → operate 1st and 2nd dc in „aquarium“ to confirm long term behaviour → chance to check for additional „hidden“ weak point (masked by „via problem“) Malte Hildebrandt MEG Review Meeting, 18.02.2009

  48. Time Schedule → following activities will start immediately and run in parallel: motto:confirm„viahypothesis“,startnewconstruction/repairworktoproofsolution detector laboratory February – March • „dc skeleton“ in aquarium • „via test“ with pcb • test new dc‘s in aquarium April – July • ongoing test in aquarium July – August • test of dc system in support structur in laboratory beginning of September → dc system ready for installation in MEG experiment detector workshop • construction of new dc‘s: anodes with new pcb recycled cathode + hood • ongoing construction Malte Hildebrandt MEG Review Meeting, 18.02.2009

  49. New DC Preamplifier • goal: • improve signal/noise ratio → improve R- and z-resolution for small signals → improve efficiency • argument: • analysis of experimental data 2007 using low-pass digital filter: → improvement in z-resolution and 10% higher efficiency • solution: • select low-noise operational amplifier • adapt schematics → bandwidth reduced from 140MHz to 80MHz • status: • few prototypes produced and tested → signal/noise ration improved by factor 1.5 • to do: • direct comparison of old and new preamplifier with real signals → dc in „aquarium“ with cosmics and 90Sr Malte Hildebrandt MEG Review Meeting, 18.02.2009

  50. Summary / Outlook • many dc planes / modules suffered from frequent HV trips • consequently theses planes / modules could only be operated with reduced HV settings → huge impact on overall performance of dc system and MEG experiment • many tests were performed in MEG experiment and in laboratory in order to understand this problem including: upgrade and construction of new laboratory infrastructure • following weak points were identified so far: • potting of HV soldering spot on pcb → seal with epoxy • HV via on pcb → anode frames with new pcb design • ongoing activities: • confirm via hypothesis • start construction/repair work to proof solution → dc system ready for installation at beginning of September Malte Hildebrandt MEG Review Meeting, 18.02.2009

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