Drift Chamber System
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Drift Chamber System • hardware status Run 2007 • shutdown activities 2008 . Malte Hildebrandt. MEG Review Meeting, 20th Feb 2008. Installation 2007. • main changes / improvements compared to installation in 2006:

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Installation 2007

Drift Chamber System

• hardware status Run 2007

• shutdown activities 2008

Malte Hildebrandt

MEG Review Meeting, 20th Feb 2008

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Installation 2007
Installation 2007

• main changes/improvements compared to installation in 2006:

• modifications of support structure ↔ clearance to N2 bag

• new design of gas manifolds ↔ less influence on e+ trajectory

• placed at larger lzl- and larger r- coordinate

• different material (0.5mm Al → 1mm PVC)

• 16/16 drift chamber modules

• as in 2006: each dc module tested in test setup „aquarium“

(He/C2H6 inside module and Helium outside module)

• cosmics run in lab, modules mounted in support structure

→ sort out cable mismatch „inside COBRA“

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift chamber system
Drift Chamber System

dc support

flange to BTS

„MEG“

target

dc15

dc00

gas manifold ds

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Alignment part 1
Alignment – Part1

• measurement of identification marks wrt reference bolts

(3D touch-sensitive sensor in mechanical workshop)

identification mark

identification mark

reference bolt

„connection“ to position of

• anode wires and

• cathode pattern

(x-y-measuring table in lab)

reference bolt

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Alignment part 2
Alignment – Part2

• surveying of identification marks wrt support structure and beam axis

( survey with theodolite by survey group)

reference holes in support structure

→ 2 vectors:

• connecting line of

adjacent holes

• middle of connecting line

to identification mark

(chamber plane)

identification marks on dc module

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Chamber shift
Chamber Shift

• observation after

measurement and survey:

• shift of modules

• tilt of modules

→ ChamberShift in data base

• corrections in x, y, z

up to 2mm

• corrections along vector

of chamber plane

up to 6mrad

upstream

displacement x50

downstream

displacement x50

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Wire displacement
Wire Displacement

• deviation(wire#) in R and Z of

expected hit point to fitted track

(including ChamberShift data)

→ measure of wire displacement

before alignment procedure

→ after 3 iterations: <0.01cm

tilt

shift

• mechanical deformation of

dc module/support structure ?

→ survey dc + target system

before installation

(„hanging“)

→ survey after installation in

COBRA

(„sitting“ )

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Survey of target
Survey of Target

• observation after dc installation (Aug. 2007): target slightly misaligned

→ „survey“ with vertical and horizontal laser projections

→ photos with digital camera and geometrical analysis (PRK)

→ numbers are included in MC

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Target
Target

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Survey of target1
Survey of Target

• observation after dc installation (Aug. 2007): target slightly misaligned

→ „survey“ with vertical and horizontal laser projections

→ photos with digital camera and geometrical analysis (PRK)

→ numbers are included in MC

• before dismounting dc system (Jan. 2008):

→ photogrammetric survey by survey group (no time for theodolite survey)

• several photos from different positions (~1h)

• analysis later with special software and camera calibration

• but: maybe problems due to small angles and glancing intersections

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Photogrammetric survey of target
Photogrammetric Survey of Target

reference

points

ruler

(absolute scale)

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Survey of target2
Survey of Target

• observation after dc installation (Aug. 2007): target slightly misaligned

→ „survey“ with vertical + horizontal laser projections

→ photos with digital camera, geometrical analysis (PRK)

→ numbers are included in MC

• before dismounting dc system (Jan. 2008):

→ photogrammetric survey by survey group (no time for theodolite survey)

• several photos from different positions (~1h)

• analysis later with special software and camera calibration

• but: maybe problems due to small angles and glancing intersections

before Run 2008: • identification marks on target/frame

• schedule theodolite survey of dc + target (~1d)

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift chamber operation
Drift Chamber Operation

• startup/de-bugging phase (noise, HV & SlowControl vs magnetic field)

• Cosmic Ray Run 11.-17.10.2007 (1.2M events)

• z-calibration

• wire positioning, alignment

• gain calibration

• standalone Michel Run (08.-14.11.2007)

→ ultra low (3M + 2M events) • xt -calibration

• Michel spectrum

→ low (2 M events) • confirm stable dc operation

at „normal“ beam intensity

• tune tracking algorithm

• MEG Run

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift chamber operation1
Drift Chamber Operation

• startup/de-bugging phase (noise, HV & SlowControl vs magnetic field)

• Cosmic Ray Run 11.-17.10.2007 (1.2M events)

• z-calibration

• wire positioning, alignment

• gain calibration

• standalone Michel Run (08.-14.11.2007)

→ ultra low (3M + 2M events) • xt -calibration

• Michel spectrum

→ normal (2 M events) • confirm stable dc operation

at „normal“ beam intensity

• tune tracking algorithm

• MEG Run

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Disconnected cables

open DS endcap

Jan 2008

disconnected patchpanel inside

Disconnected Cables

• missing LV dc6u

• missing signal channels

1anode wire = signals from both sides (out of 288)

3 anode signals = signal from one side (out of 576)

23 cathode / hood signals (out of 1152)

(only one cell with 2 missing cathode signals)

Remark: everything fine during startup, most likely explanation for mishap:

• LV cables: stiff and rigid • signal cables: slippery

→ slight mechanical tension

→ very slow movement, even we fixed with tape and cable ties

→ finally connector slips out of socket

→ improved strain-relief of cables on pcb

(design finished, parts under construction)

→ additional test after inserting dc support structure, before closing endcap

Malte Hildebrandt MEG Review Meeting, 20.02.2008


O 2 sensors

O2

O2

O2

O2

O2

O2 Sensors

US endcap

DS endcap

He_in

He_in

dc

He_out

He_out

• Alphasens O2 sensors : • metal/air battery: I proportional O2 concentration

→ calibration with 20.8% O2 → U0 = R·I0

→ “aging”: exposed to 20.8% O2 → I0 = I0(t)

• powerfull tool to monitor Helium concentration inside COBRA and to „identify“ leaks

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Dc hv problems

o

u

t

s

i

d

e

?

→ recent activities (since beginning of January):

• dc support structure moved out of COBRA

• test setup „aquarium“ installed and operational in pE5

• „weakest“ dc module dismounted → optical inspection

suspicious spot: sealing of HV connection to pcb

DC HV Problems

• 6 dc modules showed frequent HV trips (1850V) when cHe_COBRA >97%

MC: influence on • m stopping distribution and

• reconstructed momentum resolution of e+

→ decission: air admixture to „adjust“ 95% < cHe_COBRA< 97%

• but: due to trips slight deterioration during run…

→ situation end of run: 16 / 32 planes operated at 1850V

11 / 32 planes operated at 1800V

5 / 32 planes not operational (<1700V)

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Hv connection
HV Connection

hood readout

hood Vernier pattern

anode decoupling capacitors

pre-amplifier cards

HV connection to pcb

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Anode pcb
Anode PCB

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Next steps

next steps:

• all dc modules with planes labled „not operational“:

• dismount from support structure → optical inspection

• redo sealing of HV connection

• confirm HV stability in test setup „aquarium“

Next Steps

• 1st test with „weakest“ dc module in „aquarium“: HV trip reproduced

→ new sealing

→ stable operation with 1875V at 99.7% Helium in „aquarium“ (O2-sensor)

→ depending on success of these activities:

• all dc modules with planes operated at1800V:

• dismount from support structure

• check/redo sealing

(• confirm HV stability in aquarium)

• no activities scheduled for planes operated at 1850V

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Current vs beam rate
Current vs Beam Rate

• two different settings for m stopping rate :

ultra low: 5.0·106m/s

normal : 3.1·107m/s

Ianode [nA]

dc4A

m stop rate [Hz]

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Current vs hv
Current vs HV

• normal m stopping rate 3.1·107m/s

• HV scan from 1600V to 1850V

→ Ianode shows exponential relation as a function of HV!

but: slight saturation visible

• only ~10V voltage drop

due to 1M resistor and

10mA

→ saturation due to high

gain and space charge

effects?

→ analysis of pulse heigth

or charge distribution

ln(Ianode)

dc4A, low rate

HV [V]

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Wire hit rates
Wire Hit Rates

cut condition for charge : > 0.6 V·ns

→ why is 1st cell of plane A and plane B much higher than expected ?

→ why is 1st cell of plane A higher than 1st cell of plane B ?

normal rate, dc08

data

MC

H.Nishigushi

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift lines from track
Drift Lines from Track

potential wire (GND)

anode wire

B

B

A

A

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift lines from track1
Drift Lines from Track

potential wire (GND)

anode wire

B

B

A

A

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift lines from track2
Drift Lines from Track

potential wire (GND)

anode wire

B

B

A

A

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Drift lines from track3
Drift Lines from Track

potential wire (GND)

anode wire

B

B

A

A

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Mc data
MC + Data

→ after implementation of „cell 0 geometry“ in MC:

cut condition for charge : > 0.6 V·ns

normal rate, dc08

data

MC

H.Nishigushi

→ still some work to do understand further discrepancies

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Charge distribution
Charge Distribution

run 6092, 6093, low rate

wire 1

wire 2

wire 0

wire 3

wire 4

wire 5

wire 6

wire 7

wire 8

H.Nishigushi

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Current gas gain

data: •S(single wire hite rates) too large due to contributions

of small pulses on wire 0

• estimation of correction factor 0.9 (Ch.Topchyan):

→ gas gain ~4.4·105 @ 1850V

What is the reason for the small pulses?

• low collection efficiency? • GARFIELD

• attachment / recombination ? • data analysis

Current, Gas Gain

• dE/dX, r → energy deposition along track

w-value → primary ionisation along track

track length → primary ionisation per traversing particle

rate, surface → Iprimary ionisation

Iprimary ionisation x gas gain = Imeasured

• accumulated charge (innermost anode wire): ~1C/cm/8months

→ monitor chamber parameters

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Psi savety
PSI Savety

• dc gas system: • fire protected cabinet

with ventillation system

to operate 50l bottle ethane

• pE5 gas warning system: • in total 8 sensors:

3 sensors for O2

4 sensors for C2H6

1 sensor for H2

Malte Hildebrandt MEG Review Meeting, 20.02.2008


Conclusion
Conclusion

• dc hardware problems have huge impact on overall performance of

dc system

→ exchange / repair broken pre-amplifier cards

→ improve strain-relief of LV and signal cables

→ repair bad potting of HV connection on dc modules to ensure

HV stability in pure Helium environment

→ in parallel: construction of 2nd spare module (dc18)

remark: dc17 available in laboratory (completely tested)

Malte Hildebrandt MEG Review Meeting, 20.02.2008