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

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

3. Malte HildebrandtMEG Review Meeting, 18.02.2009 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)

4. Malte HildebrandtMEG Review Meeting, 18.02.2009 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)°

5. Malte HildebrandtMEG Review Meeting, 18.02.2009 Target 2007 2008

6. Malte HildebrandtMEG Review Meeting, 18.02.2009 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

7. Malte HildebrandtMEG Review Meeting, 18.02.2009 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

8. Malte HildebrandtMEG Review Meeting, 18.02.2009 New DC HV Modules 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  Controller in case of missing toggle signal from  Controller (→ 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  Controller stucks smaller capacitance at HV_output reduces trip propagation within HV module geographical addressing of nodes within crates ↔ S.Ritt ↔ R.Schmidt

9. Malte HildebrandtMEG Review Meeting, 18.02.2009 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)

10. Malte HildebrandtMEG Review Meeting, 18.02.2009 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)  beam 2 planes showed problems right from beginning phase 2:Augdc system most of the time off, short period on  beam 19 / 32 planes >1800 V 6 / 32 planes 1700-1800 V phase 3: Sep – Decfurther deterioration of HV performance  beam 11 / 32 planes>1800 V 7 / 32 planes 1700-1800 V

11. Malte HildebrandtMEG Review Meeting, 18.02.2009 Phase 1 phase 1: June – July  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 →c Helium ≈ 95-96 % (reading O 2 sensors) (instead of „pure“ helium level around 99.0-99.5 %)

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

13. Malte HildebrandtMEG Review Meeting, 18.02.2009 Phase 1 phase 1: June – July  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 →c Helium ≈ 95-96 % (reading O 2 sensors) (instead of „pure“ helium level around 99.0-99.5 %) →end of July: 30 / 32 planes operational with >1800 V (remark: nominal 1850 V) occasional problems with communication of HV modules / MSCB / LabView →modify HV modules during XEC run

14. Malte HildebrandtMEG Review Meeting, 18.02.2009 Phase 2 phase 2: August  beam, XEC run, Dalitz run XEC run: dc gas system running continuously dc HV system off for 2 ½ weeks (modifications of HV modules) 10 days dc HV at 800-1000 V Dalitz run (e + e - identification in Dalitz decay  0 → e + e -   ) 5 days dc HV on nominal values →current load / plane:0.7-1.0  A (compared to 10-12  A with  beam) but: many HV trips, number of „weak“ planes increased →beginning of September: 19 / 32 planes >1800 V 6 / 32 planes 1700-1800 V

15. Malte HildebrandtMEG Review Meeting, 18.02.2009 Phase 3 phase 3: September – December  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

16. Malte HildebrandtMEG Review Meeting, 18.02.2009 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

17. Malte HildebrandtMEG Review Meeting, 18.02.2009 HV Trips characteristics of HV trips: beginning of run period: air admixture to COBRA gas necessary to achieve stable dc operation →c Helium ≈ 95-96 % significant deterioration started after:  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  beam time stable operation (with reduced HV settings) during second  beam time (5 days) 2007:c Helium ≈ 96 % 2007:  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  beam time

18. Malte HildebrandtMEG Review Meeting, 18.02.2009 HV Trips characteristics of HV trips: beginning of run period: air admixture to COBRA gas necessary to achieve stable dc operation →c Helium ≈ 95-96 % significant deterioration started after:  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  beam time stable operation (with reduced HV settings) during second  beam time (5 days) 2007:c Helium ≈ 96 % 2007:  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  beam time →deterioration due to  beam time ?

19. Malte HildebrandtMEG Review Meeting, 18.02.2009 HV Trips characteristics of HV trips: beginning of run period: air admixture to COBRA gas necessary to achieve stable dc operation →c Helium ≈ 95-96 % significant deterioration started after:  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  beam time stable operation (with reduced HV settings) during second  beam time (5 days) 2007:c Helium ≈ 96 % 2007:  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  beam time →deterioration due to  beam time ? →deterioration due to helium environment ?

20. Malte HildebrandtMEG Review Meeting, 18.02.2009 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 (p dc -p COBRA ): ↔ small leaks ?

21. Malte HildebrandtMEG Review Meeting, 18.02.2009 Location of HV Problems HV problems at top of U-branches: systematics or just by chance ? level of dp_dc measurement dc operation at slightly lower dp_dc dc operation at slightly higher dp_dc dp → due to difference in ρ of He and He/C 2 H 6 : 15th Oct 2008

22. Malte HildebrandtMEG Review Meeting, 18.02.2009 Location of HV Problems HV problems at top of U-branches: systematics or just by chance ? level of dp_dc measurement dc operation at slightly lower dp_dc dc operation at slightly higher dp_dc → due to difference in ρ of He and He/C 2 H 6 : 15th Oct 2008 dp

23. Malte HildebrandtMEG Review Meeting, 18.02.2009 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 (p dc -p COBRA ): ↔ 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 / C 2 H 6 : 50 / 50 →45 / 55 → reduction of gas gain by nearly factor 2 → no improvement

24. Malte HildebrandtMEG Review Meeting, 18.02.2009 Tests during MEG Run increase air admixture to COBRA:↔ outside dc module phase 1: c Helium ≈ 95-96 % c Helium ≈ 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

25. Malte HildebrandtMEG Review Meeting, 18.02.2009 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)

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

27. Malte HildebrandtMEG Review Meeting, 18.02.2009 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:c Helium > 99% (reading of three O 2 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)

28. Malte HildebrandtMEG Review Meeting, 18.02.2009 2 nd Pressure Control System construction of 2 nd pressure control system for laboratory →operate „aquarium“ independently from MEG pressure control system reminder: „aquarium“:setup to operate two dc modules with He / C 2 H 6 as counting gas within helium atmosphere

29. Malte HildebrandtMEG Review Meeting, 18.02.2009 Helium Cabin closed volume (V = 5.7 m 3 ) 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 →ensures helium environment for dc system during „waiting time“ in lab →c Helium ≈ 95 % (conditions like in COBRA)

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

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

32. Malte HildebrandtMEG Review Meeting, 18.02.2009 HV Sealing cable isolation HV line dielectricum potting braided shield pcb → nominal condition →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!)

33. Malte HildebrandtMEG Review Meeting, 18.02.2009 HV Soldering Spot

34. Malte HildebrandtMEG Review Meeting, 18.02.2009 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

35. Malte HildebrandtMEG Review Meeting, 18.02.2009 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 isolatorsfine →closer look at vias on pcb

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

37. Malte HildebrandtMEG Review Meeting, 18.02.2009 dc01A no glue glue no glue

38. Malte HildebrandtMEG Review Meeting, 18.02.2009 PCB Cross Section GND +HV pcb +HV G10 isolator glue G10 isolator glue carbon frame air He / C 2 H 6 He pcb bottom layer top layer bottom layer

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

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

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

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

43. Malte HildebrandtMEG Review Meeting, 18.02.2009 Depth of HV Vias dc01A →example: depth of HV via on dc01A upstreamdownstream a00.73 ± 0.030.76 a10.470.80 a20.390.66 a30.140.83 a40.650.67 a50.570.46 a60.640.61 a70.000.47 a80.570.57 location of discharge (identified by signals) remark: all numbers in mm d design = 0.80 ± 0.02

44. Malte HildebrandtMEG Review Meeting, 18.02.2009 PCB Cross Section GND +HV pcb G10 isolator glue +HV glue G10 isolator glue carbon frame He / C 2 H 6 pcb

45. Malte HildebrandtMEG Review Meeting, 18.02.2009 Next Steps →following activities will start immediately and run in parallel: motto: confirm „via hypothesis“, start new construction / repair work to proof solution 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

46. Malte HildebrandtMEG Review Meeting, 18.02.2009 HV Print 2009 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“) vias for +HV pads for resistors +HV traces outer edge print 2007 print 2009 inner edge GND

47. Malte HildebrandtMEG Review Meeting, 18.02.2009 Next Steps →following activities will start immediately and run in parallel: motto: confirm „via hypothesis“, start new construction / repair work to proof solution 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 1 st and 2 nd dc in „aquarium“ to confirm long term behaviour →chance to check for additional „hidden“ weak point (masked by „via problem“)

48. Malte HildebrandtMEG Review Meeting, 18.02.2009 Time Schedule →following activities will start immediately and run in parallel: motto: confirm „via hypothesis“, start new construction / repair work to proof solution detector laboratory February – March „dc skeleton“ in aquarium „via test“ with pcb test new dc‘s in aquarium April – Julyongoing 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

49. Malte HildebrandtMEG Review Meeting, 18.02.2009 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 140 MHz to 80 MHz 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 90 Sr

50. Malte HildebrandtMEG Review Meeting, 18.02.2009 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