malte hildebrandt

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


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


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


Installation 2008



• 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


Target

2007 2008

Malte Hildebrandt


Installation 2008






→ identification marks on target

Malte Hildebrandt


Installation 2008






→ identification marks on target

→ measurements of inclination:

• conventional (sliding rule) 2007(2008): conventional

• photogrammetric 2007: photogrammetric • optical survey

Malte Hildebrandt


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


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


HV Performance

• summary: • many dc planes / modules suffered from frequent HV trips


→ 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


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


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


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


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


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


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


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


HV Trips









2007: cHelium ≈ 96 %

2007: at end of run




→ deterioration due to beam time ?

Malte Hildebrandt


HV Trips









2007: cHelium ≈ 96 %

2007: at end of run




→ deterioration due to beam time ?

→ deterioration due to helium environment ?

Malte Hildebrandt


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


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


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



• 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



• 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


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


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


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


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


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


Test Tesults

→ first results from dc module tests in laboratory

• weak point: potting of HV soldering spot on pcb

Malte Hildebrandt


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


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


HV Soldering Spot

Malte Hildebrandt


Test Tesults



→ replace ThreeBond 1530 with epoxy EPO-TEK 302-3M

Malte Hildebrandt


Test Tesults



→ 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


HV Via

top layer

bottom layer

+HVGND

7 mm

Malte Hildebrandt


dc01A

no glue glueno glue

Malte Hildebrandt


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


PCB Cross Section

GND +HV

pcb

G10 isolator

glue

+HV

glue glue

G10 isolator

glue

glue

carbon frame

d

pcb

Malte Hildebrandt


PCB Cross Section

GND +HV

pcb

G10 isolator

glue

+HV

glue glue

G10 isolator

glue

glue

carbon frame

pcb

Malte Hildebrandt


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


PCB Cross Section

GND +HV

pcb

G10 isolator

glue

+HV

glue

G10 isolator

glue

glue

carbon frame

He / C2H6

pcb

Malte Hildebrandt


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


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


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


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


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


Summary / Outlook

• many dc planes / modules suffered from frequent HV trips


→ 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

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