precision mechanics / systems aspects case examples from lhc trackers 1st eiroforum school on...

Precision Mechanics / Precision Mechanics / Systems AspectsSystems Aspects

Case examples from LHC TrackersCase examples from LHC Trackers

1st EIROforum School on Instrumentation1st EIROforum School on Instrumentation 11-15 May 200911-15 May 2009

A. Onnela and A. Catinaccio A. Onnela and A. Catinaccio CERN – PH/DTCERN – PH/DT

http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=43007

http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=43007

ESI 2009, 11-15 May 2009 Precision Mechanics and Systems Aspects. A.Onnela, A.Catinaccio, CERN-PH/DT 2

Intro: LHC Trackers and ‘precision’

Design

Materials

Analysis

Manufacture, Assembly

Transport, Installation

Summary: Lessons learned

Intro: LHC Trackers

Tracker in the heart of the experiment, next to the beam interaction point

ESI 2009, 11-15 May 2009 3Precision Mechanics and Systems Aspects. A.Onnela, A.Catinaccio, CERN-PH/DT

Intro: LHC Trackers

Tracker: Measurement of particle track space points with 10-50 um precision


Intro: LHC trackers


Find 4 straight tracks.

40 million times per second

Find 4 straight tracks!


Intro: LHC trackers

Here the 4 straight tracks+ few other high momentum tracks

Intro: LHC Trackers


From individual sensor units (modules) via sub-assemblies up to the final Experiment


Intro: LHC Trackers and precision

Design

Materials

Analysis





To design correctly clarify:

What is really needed?What ‘precision’ is needed?

Establishing the requirements may be difficult and take many iterations, possibly late in the project, too

Design: requirements


Design: What is really needed?

• Light weight, minimum material, “transparency” to particles

• Tight mechanical tolerances (high initial accuracy) (a few tens of microns are required for the correct positioning of the detecting modules).

• High stability, high stiffness high natural frequencies

• Short and Long term dimensional stability under load (low CTE, CME, creep)

• High radiation resistance

• Magnetic field: non-magnetic materials

• Low out-gassing and low gas permeability

Example requirements from the LHC trackers:

But as it may be too difficult / too costly / too slow to reach, therefore try to get

the real requirements on:Precision, Accuracy and Stability

Yes, this is the preferred result!


Design: Requirements on Precision

Accuracy vs. Precision

High accuracy but low precision

High precision but low accuracy

Graph: Pekaje

Both influenced by the quality of manufacture and assembly, and by static loads


Stability

High momentary precision but low stability

Stability influenced by dynamic loads, creep, vibration, temperature-, pressure-, humidity change, changing magnetic field, etc.



Loads

In addition to the ‘normal’, expected loads (gravitation, thermal, etc.) study also failure scenarios and related loads.

Examples from the Atlas inner tracker:• Transports and installation: Non-ideal support conditions or accidental loads

(difficult to estimate!)• Loss of thermal isolation of the LAr cryostat: Sudden move of tracker supports

by 3 mm (far more than the displacements under normal conditions) • Malfunctioning of cooling systems: fast heating or fast cooling of detectors

(possibly severe thermal shocks)

Design for high precision

Think up to the smallest details, e.g. connections are very important, and the error chain can be long(Modules Sub-structures Full Tracker Installation into Experiment)

Some examples on precision of (metallic) couplings:

Illustrations: J. Huopana / U. Oulu

Elastic averaging:~5 um

Pinned joints: ~5 um

Kinematic coupling:~0.5 um



More and less interesting design subjects

Modules & Layout

Cooling & Services

Structures& Interfaces

Tracker:

1. This is where the attention naturally goes

2. Some attention goes to this, too

3. Little and late attention Big problems

Pay attention also to the less interesting subjects, already early on in the design process.

Not fun, but very much necessary!



Design

Materials

Analysis





Choice of materials

Correct understanding of the design requirementsenables

Correct choice of materials

Of the LHC tracker requirements…

…all have a direct impact on the material choices.

• Light weight, minimum material, “transparency” to particles• Tight mechanical tolerances (high initial accuracy) (a few tens of microns are

required for the correct positioning of the detecting modules).• High stability, high stiffness high natural frequencies• Short and Long term dimensional stability under load (low CTE, CME, creep) • High radiation resistance • Magnetic field: non-magnetic materials• Low out-gassing and low gas permeability

Materials for a LHC tracker


For trackers a hybrid solution: Structures in CFRP, small support / cooling inserts in aluminium


•


• Documentation exists, e.g. “CERN: Compilation of radiation damage data”

• However, the products change, some materials are no longer available – some new materials are not tested yet (or not known by us)


• CFRP (carbon-fibre reinforced polymers) much favoured as tailorable for high stiffness, good strength, low mass, near zero CTE, low CME, low creep

– Typical carbon fibres:• HT (high tensile e.g. T300) E = 200-255 GPa (235 for T300)• IM (intermediate modulus e.g. T800) E = 255-315 GPa• HM (high modulus e.g. M55J) E > 315 GPa• UHM (ultra-high modulus e.g. GY-70, P120) E > 395 GPa• (Note: Aluminum: 70 GPa, Steel: 210 GPa)

– Typical matrix materials (resins):• Epoxies• Cyanate ester (10 times lower CME but usually costly)

– Typical core materials:• Nomex (aramid fibres)• Aluminium

• New interesting possibilities with non-plastic matrices– Metal matrix composites (for thermal properties, but ‘heavy’)– Carbon-carbon composites (for thermal properties)

• Availability and (dis)continuity of commercial products can be a problem




Design

Materials

Analysis





Analysis

• Stability: analyse for high stiffness, thermal behaviour, vibrations & natural frequencies, support configuration, stress levels

• All boundary conditions must be well known (by experience) or large multipliers must be introduced (or risks taken!)

• Analyses must feedback to design at early stage• Analyse carefully most stressed areas (local supports and connections)• Allow time for analysis verification by extensive testing and prototype

qualification (CFRP assemblies are often difficult to predict due to manufacturing and hybrid components)

Typical analyses:

Composite layup characterisationStatic analysis (gravity loads, loads during transports)Sub modelling, local areas, supports and connections where the real problems can be.BucklingThermalModal analysisRandom vibrationShock Analysis (transport and installation)


Examples of FEM calculations

Rigid structures high local stresses



ASIC power 5.3 WFEA

Loads during handling can be much higher than the nominal operation loads



Vibration measurements for different accelerators

Random vibration analysis on Atlas TRT barrel structure:Input power spectral density (PSD) 110-8 g2/Hz and 5% damping ratio (frequency independent) results in 11 um displacements.10x lower PSD results in 2x smaller displacement, still significant!‘Fortunately’, finally a lot of cables, so a lot of damping too...

Vibration measurements in different accelerators

1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

0 20 40 60 80 100

Frequency [Hz]

PS

D a

ccel

erat

ion

[g2/

Hz]

LEP (Aleph worst case) Strasburg

Ruthe (GE) SSC

US standard



Design

Materials

Analysis




Manufacture

Example:Manufacture of this silicon module support frame


Detector supports inserts (e.g. 11, 12, 13, and 14)Detector supports inserts (e.g. 11, 12, 13, and 14)• Define parallel planes on which the detectors Define parallel planes on which the detectors

are mountedare mounted• Planarity requirement 0.05 mmPlanarity requirement 0.05 mm

1.2 m


Manufacture

Metallic inserts

Carbon fibre piecesin ‘1 mm precision’

Accurate gluing jig

Applied concept: From modest accuracy components to assemblies of high accuracy


Assembly

756x756x


Measurements

Geometrical precision of the module supports and positioning dowel pins measured to be better than 50 m over the whole area. 4% of assemblies found out of tolerances, and corrected.

24 module supports

12 dowel pins



Manufacture


Measurements

ASIC power 5.3 WFEA

PhotogrammetryPhotogrammetry ‘‘Robotic’ armRobotic’ arm

Measurements



Example: Barrel Support Structure

ASIC power 5.3 WFEA

Measurements

And then the structures are loaded


Design hint: Choose carefully the color of the cables!




Design

Materials

Analysis





Transport and installation


Transport and installation

http://perneg.web.cern.ch/perneg/sr/SR240507/html-gallery/content/index.html


Collision predicted from 3D measurementsInstallation adjusted accordingly

Measurements up to the end



Design

Materials

Analysis





Summary: Lessons learned• Put effort into establishing clear specifications,

be prepared to do many iterations and late modifications– Accuracy, precision, stability requirements– Load conditions– Electrical, magnetic, radiation, fluids, etc.

• Aim for simplicity and clarity in the design (e.g. supports). Enough of complications will come anyways!

• Do analysis early on to direct the design choices– Back-up with prototypes and tests where suitable data not available

• Plan and ‘design’ geometry measurements right from the beginning– References, survey targets, etc.

• And last, but not at all least: Take ‘services’ = Pipework and cabling into the main design effort right from the beginning

– Remember to plan and design their testing too (leak tests, connectivity, etc.)

The end

precision mechanics / systems aspects case examples from lhc trackers 1st eiroforum school on...

Documents

measurement precision

cernphdt slide

um precision esi

mechanical precision

lhc trackers esi

catinaccio cern phdt

um precision requirements

um esi