malte hildebrandt
DESCRIPTION
Drift Chamber System • hardware status in 2009. MEG Review Meeting PSI, February 2010. Malte Hildebrandt. Outline. • reminder: HV instability problem in 2007, 2008 • summary of tests and proof of via hypothesis • repair work → new anode pcb → unexpected observations - PowerPoint PPT PresentationTRANSCRIPT
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
Malte Hildebrandt MEG Review MeetingPSI, February 2010
Drift Chamber System• hardware status in 2009
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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, 17.02.2010
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, 17.02.2010
HV Trips
• characteristics of HV trips in 2007 and 2008:
• significant deterioration of HV stability started
2007: at end of run 2008: 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 – Dec 2008: 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, 17.02.2010
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 (pdc-pCOBRA) ↔ 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, 17.02.2010
HV Tests in 2009
• tests with dc system in helium cabin • dc system inside helium environment
since 16th Jan 2009
• dc modules flushedsince 16th Jan : heliumsince 30th 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 11th 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, 17.02.2010
HV Tests in 2008 / 09
• tests in laboratory (HV test box)
• pcb, potting material
• helium environment, cHelium > 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, 17.02.2010
HV Via
top layer
bottom layer
+HVGND
7 mm
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
PCB Cross Section
GND +HV
pcb
+HV
G10 isolator
glue glue glue
G10 isolator
glue
glue
carbon frame
air
He / C2H6
He
pcb
bottom layer
top layer
bottom layer
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc01A
no glue glueno glue
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue
G10 isolator
glue
glue
carbon frame
pcb
• Why are only certain vias affected?
→ gas permeability depends on thickness of „barrier“
He / C2H6
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue
G10 isolator
glue
glue
carbon frame
pcb
• Why are only certain vias affected?
→ gas permeability depends on thickness of „barrier“
He / C2H6
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue
G10 isolator
glue
glue
carbon frame
pcb
• Why are only certain vias affected?
→ gas permeability depends on thickness of „barrier“
He / C2H6
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue
G10 isolator
glue
glue
carbon frame
He / C2H6
pcb
• Why are only certain vias affected?
→ no breakdown in He / C2H6 (confirmed by test in laboratory)
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc01 Skeleton in „Aquarium“
• dc01 skeleton: anodemiddle cathodeanode(no hood cathode)
• since 19th Feb mounted inside „aquarium“
• 19th Feb – 6th Mar : helium (30 days)
6th Mar – 9th Mar : helium / ethane (3 days)
9th Mar : HV tests („rather“ stable)
9th Mar – 20th Mar : helium (22 days)
since 20th Mar : helium / ethane (untill Mar 30th: 10 d)
since 23rd Mar : HV tests
→ 30th 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 30th)
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc01A anode 3
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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, 17.02.2010
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 depthto connect appropriate layers(like „blind hole“)
vias for +HV
pads for resistors
+HV traces
outer edgeprint 2007
print 2009
inner edge
GND
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
HV Print 2009
HV print 2009
• soldering pads for capacitors
→ round shape on inner sidewhere 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, 17.02.2010
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 bysmall G10 isolator
print 2007
print 2007
print 2009
print 2009
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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 / C2H6
• observations:
→ 14 days with HV thereof: 12 days >2 kV and
7 days 2.6 kV
→ no HV trips (trip threshold 8A)
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
Potting HV Connection
HV connection to pcb + sealing
→ weak point: potting of HV soldering spot on pcb
2006 - 2008 2009
• ThreeBond 1530 (silyl polymer) • EPO-TEK 302-3M (epoxy resin)
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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, 17.02.2010
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, 17.02.2010
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, 17.02.2010
dc09A Cathode
after touching:
dc09A cathode (foil 42) 1750 V
observations:
• aluminum coating is peeling offalong Vernier pattern
• complete length of cell_0
• damaged region:• sharp edges • sligthly extended at
etched gaps
• not symmetric to anode wirebut: „rotation“ of E-field due to
B-field in other direction
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc09A Cathode
after touching:
dc09A cathode (foil 42) 1750 V
observations:
• aluminum coating is peeling offalong Vernier pattern
• complete length of cell_0
• damaged region:• sharp edges • sligthly extended at
etched gaps
• not symmetric to anode wirebut: „rotation“ of E-field due to
B-field in other direction
→ first comment from REPIC:
• peeling off maybe due tomissing chromium underlayer
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc11B, dc14A – Cathode Foil
dc11B hood (foil 22) 1850 Vdc14A 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, 17.02.2010
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, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+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 V1850 V
r
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+B cathode (foil 28)dc14A cathode (foil 23) 1800 V
observations:
• on first sight: like scratches
but:
• not removable with cotton bud
1780 V1850 V
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+B cathode (foil 28)dc14A cathode (foil 23) 1800 V
observations:
• on first sight: like scratches
but: tiny „particles“ perfectly alignedalong tracks / scratches
• not removable with cotton bud
1780 V1850 V
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+B cathode (foil 28)dc14A cathode (foil 23) 1800 V
observations:
• on first sight: like scratches
but: tiny „particles“ perfectly alignedalong tracks / scratches
• not removable with cotton bud
1780 V1850 V
scanning electron microscope (SEM) S.Ritter (NES / LNM)
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+B cathode (foil 28)dc14A cathode (foil 23) 1800 V
observations:
• on first sight: like scratches
but: tiny „particles“ perfectly alignedalong tracks / scratches
• not removable with cotton bud
1780 V1850 V
scanning electron microscope (SEM) S.Ritter (NES / LNM)
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+B cathode (foil 28)dc14A cathode (foil 23) 1800 V
observations:
• on first sight: like scratches
→ possible reason for scratches:
1780 V1850 V
polyimide foil
aluminum
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc09, dc11, dc14
dc09A cathode (foil 42) 1750 Vdc11A+B cathode (foil 28)dc14A cathode (foil 23) 1800 V
observations:
• on first sight: like scratches
→ possible reason for scratches:
1780 V1850 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, 17.02.2010
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, 17.02.2010
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 wireNi
(C)
Cr
Si Cr Ni
remark: C maybe due to sticker on sample table
Ni
(C)
Cr
Si Cr Ni
Ni balance Cr 18 - 20 %Si 1.5 %Al 1000 ppm, Fe 2000 ppm, Mn 2000 ppm
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
dc11B, dc14A – Anode WiresNi / Cr (80 / 20) 25 m
scanning electron microscope (SEM) + energy-dispersed x-ray spectroscopy (EDX)S.Ritter (NES / LNM)
Ni
(C)Cr
Si Cr NiO
Ni
C
Cr
SiCr Ni
O
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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 deterioratethe 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, 17.02.2010
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 (2 + 16 )
August • further tests, prepare support structure and reserve
1st September → installation of dc system in MEG experiment
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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, 17.02.2010
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 pcbwith 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, 17.02.2010
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, 17.02.2010
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·Inormal)
• 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, 17.02.2010
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 awayremark: no gas gain below ~1300 V
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
Dark / Remaining Currents
dc14A
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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 awayremark: 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 (1st Townsend coefficient)
e- emission at cathode due to field emission
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
Malter Effect
cathode
anode wire
isolating film / layer
e- →← +
cathode
anode wire
isolating film / layer
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, 17.02.2010
Malter Effect
cathode
anode wire
isolating film / layer
e- →
cathode
anode wire
isolating film / layer
e- →
++++
+
++
• hugh electrical field strengthbetween surface of isolating filmand 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-
3 4
Louis Malter, Phys.Rev. 50 (1936) 48-58: Thin Film Field Emission
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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 awayremark: 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 (1st 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, 17.02.2010
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, 17.02.2010
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 filmto 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 SiO2 underlayer on polyimid film
→ very good adhesion of aluminum→ advantage: SiO2 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, 17.02.2010
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: 2nd etching removes partially Aluminum layer
→ option A failed !
cross markers nearly lost jaggy edges
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
New Cathode Foil
• option B: • 1 nm SiO2 underlayer on polyimid film
→ very good adhesion of aluminum
→ advantage: SiO2 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:
• SiO2 is isolator → charging up in high rate environment ?
• Si may lead to aging in gaseous detector
• SiO2 is electron supplier (e.g. in muonium production)
→ starting point of discharges ?
→ option B was rejected !
Malte Hildebrandt
MEG Review Meeting, 17.02.2010
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, 17.02.2010
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: 2nd 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, 17.02.2010
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, 17.02.2010
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 2009.
• 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 2009.→ 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