1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 1/16

Ageing Phenomena in the LHCb Outer Tracker

1 November 2007IEEE2007

Niels TuningOn behalf of the LHCb Outer

Tracker Collaboration

o Introductiono Ageing Phenomenono Causeo Treatments

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 2/16

LHCb in a nutshell

Aim: look for new physics by measuring CP violation and rare decays

• pp with s =14 TeV• L = 2.1032 cm-2s-1

• 1012 b-hadrons per year

b

s

s

b

b s

μ

μ

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 3/16

The LHCb Tracking System

Tracking Detectors

Outer TrackerStraw tube technologyGaseousMomentumB-mass

Trigger TrackerInner TrackerSi strip detector

Vertex Locatorn-on-n Si strip detector8mm from LHC beam Impact parameter B-lifetime

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 4/16

Outer Tracker

340 mm Total nr of channels:

53.760 Gas: Ar/CO2 70/30 Anode: 25µm W/Au Cathode: Kapton XC/Al

One large straw tube module: 34 x 490 cm2

4 x 64 = 256 straw tubes

5m

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 5/16

Position

Good Example:

Check detector response:• Current from 90Sr β-source• Pulse height from monochromatic 55Fe γ-

source

• Full scan of the entire module Every cm2 of the OT is checked

Wire locators

Final Module Check:radioactive source scan

C

urre

nt (n

A)

Example of uniform response

5 meter

Bad Example:

# W

ire

+20%

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Ageing Phenomenon (I)

o Gain loss “in the neighborhood” of the irradiation point:

Croissant? Bean? Kidney? Only at moderate intensity Upstream of gas flow

A real surprise – this was not seen in the aging tests performed over the last years with test modules

Ratio Plot: Iafter/Ibefore Irradiate with 2 mCi 90Sr source150nAGas flow

Ageing Studies in R&D phase with test module:

o 12 MeV proton beamo Hadronic environment (in situ HERA-B)o 9 keV X-ray tube:

Intermezzo:Ageing Studies in R&D phase

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 7/16

IEEE 2004 NSS-MIC conference (Oct 2004, Rome) by Sebastian Bachmann Session N39: Radiation Damage Effects II - Aging of Gaseous Detectors Title: Ageing Studies for the Straw Tube Detectors for the LHCb Outer

Tracking System

Accumulated 3 C/cm in 120 daysNo effects seen

Ageing Phenomenon (II)

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 8/16

o Gain loss “in the neighborhood” of the irradiation point: Only at moderate intensity Upstream of gas flow

Gas flowRe

lati

ve g

ain

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Wire InspectionDeposit on the surface?

Carbon

Non-irradiated wire

Irradiated wire

SEM-EDX:

Optical:

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Find the Culprit(s)

Philosophy:• Create module without glue• Add component by component, until it

ages

Normal F-module:20 hrs, 20mCi

Test module (straws):480 hrs, 20mCi

Test module

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 11/16

Find the Culprit

Put fresh glue at straw entrance Ageing

Test module:17 hrs, 2 mCi

In parallel, new test modules are built with different glue Confirm malicious effect of glue

Glue: AralditeAW103, HY991

Ageing: Treatments (I)

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 12/16

• Beneficial effects: Heating (2 weeks at 45

oC) Flushing HV training

No heating: 20 hrs 2mCi 90Sr

With heating: 325 hrs 2mCi 90Sr

Ageing: Treatments (I)

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• Beneficial effects: Heating (2 weeks at 45

oC) Flushing HV training

Flushing Time (weeks)

G

ain

loss

(%)

No heating: 20 hrs 2mCi 90Sr

With heating: 325 hrs 2mCi 90Sr

½ year

Detector is installed, and flushing since 1 year

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Ageing: Treatments (II)

• Beneficial effects: Heating Flushing HV training (24 hrs, 1900V,

G~700k) Dark current ~ 10µA / wire Wire inspection promising;

no carbon deposits despite large currents

2nd HV training

1st HV training

3rd HV training R

elat

ive

Gai

n

Irradiation Time (hours)• Other beneficial effects:

Lower gas flow during operation Addition of O2 to counting gas

Ageing: Treatments (III)

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• Other beneficial effects: Lower gas flow during

operationAr/CO2 70/30, 22hrs, 20 l/hr

Ar/CO2/O2 70/27.5/2.5, 46hrs, 10 l/hr

Addition of O2 to counting gas

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 16/16

Summary

o Observed serious gain loss with modest irradiation No gain loss at highest intensity No gain loss downstream the source

o Outgassing glue is found to be the causeo Various treatments have been identified

Flushing Heating HV training Lower gas flow Addition of O2

What science we’ll know in 2050

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 17/16

o The December 1999 issue of Scientific American, cited eight questions to which science is likely to have found the answers by the year 2050:

Can physics be unified?

Can aging be postponed?

How was the Universe born?

How does the mind work?

What secrets do genes hold?

Can robots be intelligent?

Is there life in outer space?

How much do we change the climate?

Backup slides

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Consequence for LHCb?

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 19/16

o Difficult to predict consequence: Relate source to LHCb

Source LHCbnA/straw

/cm

nA/straw

/cm

Consequence for LHCb?

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 20/16

o Difficult to predict consequence: Relate source to LHCb Add all beneficial effects

• Multiplicative? Extrapolate damage to 108

s• Linearly?• Exponentially?

20 hrs 90Sr

320 hrs 90Sr

(~106 s)

Gas flow 5l/h

(1V/3.6 h)

Extrapolateexponentiall

y to 3×107s

Extrapolatelinearly

to 3×107s

×1/2 ×7 ×26

Heated Module - 2% 1% 7% 26%Flushed Module 2% 15% 8% 56% -

NBAll numbers are for the region of maximum damage (“hot spot”)E.g. 10 cm (in Y) away from that, numbers have to be scaled down by a factor 23

Consequence for LHCb?

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 21/16

o Difficult to predict consequence: Relate source to LHCb Add all beneficial effects

• Multiplicative? Extrapolate damage to 108

s• Linearly?• Exponentially?

Low gas gain cell efficiency

• Gain drop of 50% is roughly equivalent to a HV step of ~70 V

• Assume an initial operational voltage of 1520 V Gain drop of 50% ~ effective HV reduction of 70V ~15% lower drift-cell efficiency

Consequence for LHCb?

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 22/16

o Difficult to predict consequence: Relate source to LHCb Add all beneficial effects

• Multiplicative? Extrapolate damage to 108

s• Linearly?• Exponentially?

Low gas gain cell efficiency

Cell eff track efficiencyTr

acki

ng e

fficie

ncy

OT-cell efficiency

Nominal

An OT-cell efficiency 15% lower than nominal over the entire detector surface induces a 8% reduction of the tracking efficiency

CAVEATThis study is purely illustrational! tracking is not optimized to handle significant reductions of cell efficiencies the gain loss and thus the reduction of cell efficiency is far from being uniform!

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Reverse gas flow

• Only ageing close to input• Polution not caused at curing

time Classical outgassing after

all

Gas flow

Gas flow

Close to output

Close to input

(12 Jun 07, #24)

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Reverse gas flow, check other output now

• Only ageing close to input• Polution not caused at curing

time Classical outgassing after

all

Gas flow

Gas flow

Close to input

(14 Jun 07)

Confirm Gain Loss with 55Fe pulse height

1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 26/16

• Gain loss measured with Current from 90Sr Pulse height from 55Fe