Malte Hildebrandt MEG Review Meeting, Malte Hildebrandt MEG Review Meeting PSI, February 2010 Drift Chamber System hardware status in 2009

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, HV Trips characteristics of HV trips in 2007 and 2008: significant deterioration of HV stability started 2007:  at end of run2008:  beam time (XEC, Dalitz) 2007: after 2-3 months with 2008: after 2-3 months with gas and HV gas and HV →at beginning: same planes affected as in 2007 further deterioration during remaining run time even without any further  beam time 2007: Sep – Dec2008: May – Dec stable operation with reduced HV settings 2007: dc system off during 2008: second  beam time  beam time →deterioration due to helium environment ? Reminder

Malte Hildebrandt MEG Review Meeting, HV Tests in 2008 tests with dc system in MEG during run 2008: exchange of infrastructure / hardware (HV module, HV cables) variation of dp_dc regulation value (p dc -p COBRA )↔ small leaks ? increase ethane fraction in dc counting gas ↔ inside sensitive volume ? increase air admixture to COBRA↔ outside dc module ? →no clear cause and effect (on shorterm scale) →but: hint, that problem is connected to longterm exposure to helium Reminder

Malte Hildebrandt MEG Review Meeting, HV Tests in 2009 tests with dc system in helium cabin dc system inside helium environment since 16 th Jan 2009 dc modules flushed since 16 th Jan : helium since 30 th Jan : helium / ethan operated with MEG dc HV system goal: investigate HV status compare with HV status at end of last years run identify characteristics of weak anode channels observations (tests finished 11 th May) : „weak“ planes (run 2008) got worse „good“ planes (run 2008) started to deteriorate all weak anode channels showed same signal characteristics →further proof for assumptions:HV problem related to exposure to helium (most likely) same reason for HV instabilities →4 ½ additional months „run conditions“ after end of run 2008

Malte Hildebrandt MEG Review Meeting, HV Tests in 2008 / 09 tests in laboratory (HV test box) pcb, potting material helium environment, c Helium > 99% T ≈40-45° C HV = 2 kV longterm test (>3 months) →no deterioration finally, only one topic remained on our list of suspicious and possible weak points concerning construction and operation of the drift chambers: → the bottom layer of anode HV pcb where the HV via is facing the GND layer Reminder

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

Malte Hildebrandt MEG Review Meeting, 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

Malte Hildebrandt MEG Review Meeting, dc01A no glue glue no glue

Malte Hildebrandt MEG Review Meeting, PCB Cross Section GND +HV pcb G10 isolator glue +HV glue G10 isolator glue carbon frame pcb Why are only certain vias affected? → gas permeability depends on thickness of „barrier“ He / C 2 H 6

Malte Hildebrandt MEG Review Meeting, PCB Cross Section GND +HV pcb G10 isolator glue +HV glue G10 isolator glue carbon frame pcb Why are only certain vias affected? → gas permeability depends on thickness of „barrier“ He / C 2 H 6

Malte Hildebrandt MEG Review Meeting, PCB Cross Section GND +HV pcb G10 isolator glue +HV glue G10 isolator glue carbon frame pcb Why are only certain vias affected? → gas permeability depends on thickness of „barrier“ He / C 2 H 6

Malte Hildebrandt MEG Review Meeting, PCB Cross Section GND +HV pcb G10 isolator glue +HV glue G10 isolator glue carbon frame He / C 2 H 6 pcb Why are only certain vias affected? → no breakdown in He / C 2 H 6 (confirmed by test in laboratory)

Malte Hildebrandt MEG Review Meeting, dc01 Skeleton in „Aquarium“ dc01 skeleton:anode middle cathode anode (no hood cathode) since 19 th Feb mounted inside „aquarium“ 19 th Feb – 6 th Mar : helium (30 days) 6 th Mar – 9 th Mar :helium / ethane (3 days) 9 th Mar : HV tests („rather“ stable) 9 th Mar – 20 th Mar :helium (22 days) since 20 th Mar : helium / ethane (untill Mar 30 th : 10 d) since 23 rd Mar : HV tests →30 th Mar :dc01A: first direct / optical observation of discharges between HV via and GND surface on bottom side of HV pcb → characteristics of signals on oscilloscope same as in Jan / Feb when complete dc01 was tested in „aquarium“ but now: no hood, no G10 isolators →65 days „run conditions“ (up to Mar 30 th )

Malte Hildebrandt MEG Review Meeting, dc01A anode 3

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, 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 appropriate layers (like „blind hole“) vias for +HV pads for resistors +HV traces outer edge print 2007 print 2009 inner edge GND

Malte Hildebrandt MEG Review Meeting, HV Print 2009 HV print 2009 soldering pads for capacitors → round shape on inner side where electrodes of capacitor face to each other vias for readout connectors soldering pads for decoupling capacitors +HV traces in middle layer print 2007 print 2009

Malte Hildebrandt MEG Review Meeting, HV Print 2009 HV print 2009 tracks and vias for HV on top layer → place HV („blind“) vias close to soldering pads →HV tracks are not covered by small G10 isolator print 2007 print 2009

Malte Hildebrandt MEG Review Meeting, DC Wing Test Setup „dc wing test setup“ in HV test box represents the cross section through wing of dc plane → anode frame – G10 isolators – pcb – G10 isolator – G10 isolator – hood frame goal: investigate HV stability discharges due to „polarisation“ effects ? operated in exhaust line of „aquarium“ →flushed with He / C 2 H 6 observations: →14 days with HV thereof: 12 days >2 kV and 7 days 2.6 kV → no HV trips (trip threshold 8  A)

Malte Hildebrandt MEG Review Meeting, Potting HV Connection HV connection to pcb + sealing → weak point: potting of HV soldering spot on pcb ThreeBond 1530 (silyl polymer) EPO-TEK 302-3M (epoxy resin)

Malte Hildebrandt MEG Review Meeting, DC Repair Work successful „dc wing test“ was starting signal of dc repair work ↔ all materials were already prepared in advance and on spec all dc modules were disassembled → middle cathode and cathode hood were recycled without any change → anode frames: new anode pcb‘s were glued on anode frames new wires were soldered on the pcbs / frames assembly of „new“ dc modules → module #1 and #2 operated in „aquarium“ for 6 ½ months → 16 dc modules for MEG: each individual chamber tested inside helium cabin with cosmic rays (HV, LV + signal) complete dc system tested inside helium cabin (only HV) operation in MEG: 4 months (Sep – Dec) → No deterioration of HV stability during 2009 !

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, Unexpected Phenomena during disassembly several unexpected phenomena were observed on a limited number of cathode foils and their corresponding anodes: „damage“ of cathode foil

Malte Hildebrandt MEG Review Meeting, dc09A Cathode after touching: dc09A cathode (foil 42) 1750 V observations: aluminum coating is peeling off along Vernier pattern complete length of cell_0 damaged region: sharp edges sligthly extended at etched gaps not symmetric to anode wire but:„rotation“ of E-field due to B-field in other direction

Malte Hildebrandt MEG Review Meeting, dc09A Cathode after touching: dc09A cathode (foil 42) 1750 V observations: aluminum coating is peeling off along Vernier pattern complete length of cell_0 damaged region: sharp edges sligthly extended at etched gaps not symmetric to anode wire but:„rotation“ of E-field due to B-field in other direction →first comment from REPIC: peeling off maybe due to missing chromium underlayer

Malte Hildebrandt MEG Review Meeting, dc11B, dc14A – Cathode Foil dc11B hood (foil 22) 1850 V dc14A cathode (foil 25) 1800 V observations: “spots” / peaks along Vernier pattern mainly on complete length of cell 0, but also at frame edges: cell 1, cell 2, cell 3 and cell 4 damaged region: sharp edges sligthly extended at etched gaps not symmetric to anode wire anode wires: mechanical tension ok → separate transparency potential wires: ok (?)

Malte Hildebrandt MEG Review Meeting, dc11B, dc14A – Cathode Foil topography contrast methode scanning electron microscope (SEM) + energy-dispersed x-ray spectroscopy (EDX) S.Ritter (NES / LNM) Al O Mg Al O Mg

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: white “shadows” along Vernier pattern intensity decreasing with r (rate effect?) not continuous in r, but separated stripes not symmetric to anode wire anode wires: mechanical tension ok → separate transparency potential wires: ok (?) 1780 V 1850 V r

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: on first sight: like scratches but: not removable with cotton bud 1780 V 1850 V

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: on first sight: like scratches but: tiny „particles“ perfectly aligned along tracks / scratches not removable with cotton bud 1780 V 1850 V

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: on first sight: like scratches but: tiny „particles“ perfectly aligned along tracks / scratches not removable with cotton bud 1780 V 1850 V scanning electron microscope (SEM) S.Ritter (NES / LNM)

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: on first sight: like scratches but: tiny „particles“ perfectly aligned along tracks / scratches not removable with cotton bud 1780 V 1850 V scanning electron microscope (SEM) S.Ritter (NES / LNM)

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 foil particle remark: sample table made of aluminum scanning electron microscope (SEM) + energy-dispersed x-ray spectroscopy (EDX) S.Ritter (NES / LNM) Al (O) (Mg) Al O Mg

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: on first sight: like scratches → possible reason for scratches: 1780 V 1850 V polyimide foil aluminum

Malte Hildebrandt MEG Review Meeting, dc09, dc11, dc14 dc09A cathode (foil 42) 1750 V dc11A+B cathode (foil 28) dc14A cathode (foil 23) 1800 V observations: on first sight: like scratches → possible reason for scratches: 1780 V 1850 V polyimide foil sheet of paper → improve packaging for further delivery: soft, slightly sticking foil instead of sheet of paper

Malte Hildebrandt MEG Review Meeting, Unexpected Observations during disassembly several unexpected phenomena were observed on a limited number of cathode foils and their corresponding anodes: „damage“ of cathode foil coating on anode wires

Malte Hildebrandt MEG Review Meeting, dc11B, dc14A – Anode Wires Ni / Cr (80 / 20) 25  m EHT = 10 kV EHT = 20 kV scanning electron microscope (SEM) + energy-dispersed x-ray spectroscopy (EDX) S.Ritter (NES / LNM) new wire Ni (C) Cr Si Cr Ni remark: C maybe due to sticker on sample table Ni (C) Cr Si Cr Ni Nibalance Cr % Si 1.5 % Al 1000 ppm, Fe 2000 ppm, Mn 2000 ppm

Malte Hildebrandt MEG Review Meeting, dc11B, dc14A – Anode Wires Ni / Cr (80 / 20) 25  m scanning electron microscope (SEM) + energy-dispersed x-ray spectroscopy (EDX) S.Ritter (NES / LNM) Ni (C) Cr Si Cr Ni O C Cr Si Cr Ni O

Malte Hildebrandt MEG Review Meeting, Unexpected Observations during disassembly several unexpected phenomena were observed on a limited number of cathode foils and their corresponding anodes: „damage“ of cathode foil coating on anode wires evaluation of the damage: effects are limited to a very small number of cathode foils / anode wire frames damage of cathode foil as well as coating on anode wires did not deteriorate the performance of the specific chamber ↔ theses modules were operated at nominal / nearly nominal HV until the end of the run 2008 → check carefully for dc modules which will be disassembled this spring shutdown

Malte Hildebrandt MEG Review Meeting, DC Repair Work summary of dc repair work: 2 dc modules in „aquarium“ for longterm test 16 dc modules in MEG experiment 3 sets of spare frames (modules with damaged cathode foil) → order new foil February – April „dc skeleton“ in aquarium discussion / design / tests of new anode pcb May – July construction of new dc‘s → test 2 new dc‘s in aquarium → test of mounted dc modules in support structur July middle of July: 16 dc modules in support structure → close helium cabin end of July: repair / construction work finished ( ) Augustfurther tests, prepare support structure and reserve 1 st September → installation of dc system in MEG experiment

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, Strain Relief at Inside PatchPanel location: signal / LV cables inside patch panel problem: missing dc signal channels / LV channel (2006, 2007) →shutdown 2008: improve strain relief of cables on pcb with aluminum clamps → no LV lost, reduced number of missing signal channels → but: weak point shiftet to the connector / socket on patch panel pcb installation 2009: 1 signal cable pcb completely disconnected 1 partially disconnected → intensive repair work to fix and to recover ~24 signals (endoscope, sawing, sealing, …) →shutdown 2010: improve strain relief of signal cable pcb on patch panel pcb with bracket

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, DC Performance 2009 dc04B: cosmic test in laboratory: nominal HV, normal puls height during MEG run: nominal HV, but: low gas gain (I ≈ 0.2·I normal ) cosmic run in MEG (Jan2010) nominal HV, normal puls height → not yet understood dc08B: cosmic test in laboratory: nominal HV, no HV trips at beginning of MEG run: nominal HV, periodic HV trips: 1  per 1-2 d during MEG run 3 weeks stable, then again: 1  per 1-2 d cosmic run in MEG (Jan2010) nominal HV, no HV trips → charging up effect ? dc04, dc05, dc06, dc11: MEG run: increasing dark / remaining currents → reduced HV, but still >1800 V → replace during spring shutdown all other dc modules on nominal HV → 30 / 32 planes on HV >1800 V ! 4 months operation with flushing gas 3 ½ months operation with HV and rate

Malte Hildebrandt MEG Review Meeting, Dark / Remaining Currents observations:some dc planes show dark / remaining currents (up to several  A) current starts during high rate irradiation remaining current stays, even when irradiation has finished only if HV is reduced to 1300 V, remaining current dies away remark: no gas gain below ~1300 V

Malte Hildebrandt MEG Review Meeting, Dark / Remaining Currents dc14A

Malte Hildebrandt MEG Review Meeting, Dark / Remaining Currents observations:some dc planes show dark / remaining currents (up to several  A) current starts during high rate irradiation remaining current stays, even when irradiation has finished only if HV is reduced to 1300 V, remaining current dies away remark: no gas gain below ~1300 V → hint: self-sustaining discharge (not surface current, …) → certain primary charge density necessary to start gaseous discharge → once started it remains even without source of primary charge Malter effect:e - multiplication at anode wire (1 st Townsend coefficient) e - emission at cathode due to field emission

Malte Hildebrandt MEG Review Meeting, Malter Effect cathode anode wire isolating film / layer e- →e- → ← + cathode anode wire isolating film / layer e- →e- → insulating film / layer on cathode primary charge due to irradiation motion of charge due to electrical field small surface conductivity →rate of charge build up higher than its removal rate 1 2 Louis Malter, Phys.Rev. 50 (1936) 48-58: Thin Film Field Emission

Malte Hildebrandt MEG Review Meeting, Malter Effect cathode anode wire isolating film / layer e- →e- → cathode anode wire isolating film / layer e- →e- → hugh electrical field strength between surface of isolating film and cathode →electron emission from cathode electron emission / current remains even after stop of „primary charge“ due to irradiation with beam → reduce HV until current dies away e-e- e-e- 3 4 Louis Malter, Phys.Rev. 50 (1936) 48-58: Thin Film Field Emission

Malte Hildebrandt MEG Review Meeting, Dark / Remaining Currents observations:some dc planes show dark / remaining currents (up to several  A) current starts during high rate irradiation remaining current stays, even when irradiation has finished only if HV is reduced to 1300 V, remaining current dies away remark: no gas gain below ~1300 V → hint: self-sustaining discharge (and surface current, …) → certain primary charge density necessary to start gaseous discharge → once started it remains even without source of primary charge Malter effect:e - multiplication at anode wire (1 st Townsend coefficient) e - emission at cathode due to field emission → remark from REPIC: maybe remaining photoresist on cathode foil… → improved and intensified cleaning procedure for new foils !

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, New Cathode Foil situation July 2009 after observation of damaged cathode foils need of new foils to prepare spare modules for Run 2010 improve adhesion of aluminum sputtering on polyimid film to avoid peeling off of aluminum from polyimid improve and intensify cleaning procedure to remove photo resist improve packaging to avoid micro-scratches on aluminum → 3 options: option A: 1 nm Ni-Cr underlayer on polyimid film →very good adhesion of aluminum →but: double-etching process →Al may be affected during Ni-Cr etching option B: 1 nm SiO 2 underlayer on polyimid film →very good adhesion of aluminum →advantage:SiO 2 is not conductive, remains in gaps → only single-etching process option C: samed design as 2005 production series(no underlayer) →just „backup solution“, in case A and B fail

Malte Hildebrandt MEG Review Meeting, New Cathode Foil option A:1 nm Ni-Cr underlayer on polyimid film →very good adhesion of aluminum →but: double-etching process, Al may be affected during Ni-Cr etching →result: 2 nd etching removes partially Aluminum layer → option A failed ! cross markers nearly lost jaggy edges

Malte Hildebrandt MEG Review Meeting, New Cathode Foil option B:1 nm SiO 2 underlayer on polyimid film →very good adhesion of aluminum →advantage:SiO 2 is not conductive and may remain in gaps → only single-etching process →result: very good quality (adhesion of aluminum, shape of pattern) but several concerns: SiO 2 is isolator →charging up in high rate environment ? Si may lead to aging in gaseous detector SiO 2 is electron supplier (e.g. in muonium production) →starting point of discharges ? → option B was rejected !

Malte Hildebrandt MEG Review Meeting, New Cathode Foil option C:same design as 2005 production series(no underlayer) →„backup solution“, in case A and B fail →result: very poor adhesion of aluminum layer, worse than in 2005 (different polyimid ?) → option C failed ! aluminum removed with sticky tape

Malte Hildebrandt MEG Review Meeting, New Cathode Foil option A:1 nm Ni-Cr underlayer on polyimid film →very good adhesion of aluminum →but: double-etching process, Al may be affected during Ni-Cr etching →result: 2 nd etching removes partially Aluminum layer → option A failed ! option A’:0.5 nm Ni-Cr underlayer on polyimid film → after adjusting (nearly) all sputtering and etching parameters: excellent → foil production finally started middle of December 2009 (order in July) → first delivery to PSI: beginning of January 2010 cross markers nearly lost jaggy edges

Malte Hildebrandt MEG Review Meeting, Outline reminder: HV instability problem in 2007, 2008 summary of tests and proof of via hypothesis repair work → new anode pcb → unexpected observations installation 2009 MEG Run 2009→ remaining currents new cathode foil Summary / Outlook

Malte Hildebrandt MEG Review Meeting, Summary / Outlook The reason for the HV instability problem in 2007 and 2008 was identified. The new anode pcb design eliminates this weak point. → There was no „system-wide“ HV instability problem during run During the repair work several unexpected phenomena were discovered: limited number of damaged cathode foils and coating on anode wires →for 2009: anode wire were exchanged (due to new anode pcb anyway) →for 2010: 20 new cathode foils with Ni-Cr underlayer are produced → We have to check very carefully the dc modules which will be disassembled during this spring shutdown. A few dc planes suffered from dark / remaining currents during the run →New cathode foils underwent an improved and intensified cleaning procedure to avoid possible starting points of Malter effect. The dc construction tools need to be modified and adapted to the pitch of the etched gaps of the new cathode foils. →construction of new dc modules will start end of February (min. 4 modules) →dc system will be ready for installation middle of April