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Malte Hildebrandt
MEG Review Meeting, 18.02.2009
Malte Hildebrandt MEG Review MeetingFeb 2009
Drift Chamber System• hardware status Run 2008• shutdown activities 2009
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
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
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 includesslope 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
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 misalignednew 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
Target
2007 2008
Malte Hildebrandt
MEG 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 misalignednew 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
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 misalignednew 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
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
Malte Hildebrandt
MEG 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)
Malte Hildebrandt
MEG 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: Aug • dc system most of the time off, short period on beam
• 19 / 32 planes >1800 V• 6 / 32 planes 1700-1800 V
• phase 3: Sep – Dec • further deterioration of HV performance beam
• 11 / 32 planes >1800 V • 7 / 32 planes 1700-1800 V
Malte Hildebrandt
MEG 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
→ cHelium ≈ 95-96 % (reading O2 sensors)
(instead of „pure“ helium level around 99.0-99.5 %)
Malte Hildebrandt
MEG 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 %)
cHelium=95 %
cHelium=99 %
Sat, 12.07., 15:00 32ccm / 2000ccm(1.60 %)
Mon, 30.06., 08:15 30ccm / 2000ccm(1.5 %)
Mon, 30.06., 17:4565ccm / 2000ccm(3.25 %)
cHe= ~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 %
Malte Hildebrandt
MEG 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
→ cHelium ≈ 95-96 % (reading O2 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
Malte Hildebrandt
MEG 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
Malte Hildebrandt
MEG 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
Malte Hildebrandt
MEG 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
Malte Hildebrandt
MEG 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→ cHelium ≈ 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: cHelium ≈ 96 %
2007: at end of run
2007: after 2-3 monthswith gas and HV
2007: similar, but:shorter run time(Sep – Dec)
2007: dc system offduring beam time
Malte Hildebrandt
MEG 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→ cHelium ≈ 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: cHelium ≈ 96 %
2007: at end of run
2007: after 2-3 monthswith gas and HV
2007: similar, but:shorter run time(Sep – Dec)
2007: dc system offduring beam time
→ deterioration due to beam time ?
Malte Hildebrandt
MEG 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→ cHelium ≈ 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: cHelium ≈ 96 %
2007: at end of run
2007: after 2-3 monthswith gas and HV
2007: similar, but:shorter run time(Sep – Dec)
2007: dc system offduring beam time
→ deterioration due to beam time ?
→ deterioration due to helium environment ?
Malte Hildebrandt
MEG 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 (pdc-pCOBRA): • ↔ small leaks ?
Malte Hildebrandt
MEG 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/C2H6:
15th Oct 2008
Malte Hildebrandt
MEG 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/C2H6:
15th Oct 2008
dp
Malte Hildebrandt
MEG 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 (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
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
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 spot2007: 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
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
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
2nd Pressure Control System
• construction of 2nd pressure control system for laboratory
→ operate „aquarium“ independentlyfrom 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
Helium Cabin
• closed volume (V = 5.7 m3)
• 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
→ cHelium ≈ 95 % (conditions like in COBRA)
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
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
HV Connection
anode decoupling capacitorshood readouthood Vernier pattern
pre-amplifier cardsHV connection to pcb + sealing
→ weak point: potting of HV soldering spot on pcb
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
HV Sealing
cable isolation
HV line
dielectricum
potting
braided shield
pcb
→ nominal condition
→ observation after run periodseveral 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
HV Soldering Spot
Malte Hildebrandt
MEG 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
Malte Hildebrandt
MEG 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 volumemaybe 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
HV Via
top layer
bottom layer
+HVGND
7 mm
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
dc01A
no glue glueno glue
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
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, 18.02.2009
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue glue
G10 isolator
glue
glue
carbon frame
d
pcb
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue glue
G10 isolator
glue
glue
carbon frame
d
pcb
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue glue
G10 isolator
glue
glue
carbon frame
d
pcb
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue glue
G10 isolator
glue
glue
carbon frame
pcb
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
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
location of discharge(identified by signals)
remark: all numbers in mm
ddesign = 0.80 ± 0.02
Malte Hildebrandt
MEG Review Meeting, 18.02.2009
PCB Cross Section
GND +HV
pcb
G10 isolator
glue
+HV
glue
G10 isolator
glue
glue
carbon frame
He / C2H6
pcb
Malte Hildebrandt
MEG 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
Malte Hildebrandt
MEG 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 depthto connect appropiate 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, 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 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
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 – 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 pcbrecycled cathode + hood
• ongoing construction
Malte Hildebrandt
MEG 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 90Sr
Malte Hildebrandt
MEG 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
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