Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI1 TPC Laser system Functions of the...

Laser Design Review, CERN, 27 Jan 2003 Børge Svane Nielsen, NBI 1

TPC Laser systemTPC Laser system

Functions of the system Basics of the design Construction tolerances and alignment Lab tests at NBI Status of system components Production status and installation

Design Review, CERN, 27 January 2003Børge S. Nielsen, J.J. Gaardhøje, N. Lindegaard

and Jørn Westergaard

Niels Bohr Institute

A. Lebedev, Brookhaven National Laboratory


Laser system objectives

• Electronics testing• Sector alignment• Drift velocity monitoring

– Pressure, temperature– Temperature gradients (stratification?)– ExB effects, space charge

• Two possible approaches:– Relative measurements, rely only on time stability of laser

ray position– Absolute measurements, requires knowledge of absolute

position of laser ray. More ambitious


TPC Laser principleTPC Laser principle

20-40 μJ/pulse, = 1 mm

266 nm, 100 mJ/pulse, 5 ns pulse, = 25 mm


Beam pattern inside TPCBeam pattern inside TPCRadial beamsStratetic sector boundary crossingsAvoid laser beam crossings8 ’layers’ of rays along z

336 laser tracks in full TPC


Spectron Laser Systems (UK): model SL805-10-UPGPulsed UV laser (Nd:YAG): 100 mJ / 5 ns pulse @ 266 nm, max 10 Hz expanded beam = 25 mm divergence < 0.35 mrad, pointing stability < 0.1 mrad remote controllable (RS-232)

Spectron Laser Systems (UK): model SL805-10-UPGPulsed UV laser (Nd:YAG): 100 mJ / 5 ns pulse @ 266 nm, max 10 Hz expanded beam = 25 mm divergence < 0.35 mrad, pointing stability < 0.1 mrad remote controllable (RS-232)

UV laserUV laser


Laser hut and laser beam transport (1)






Beam transport on TPC end plates (1)Beam transport on TPC end plates (1)

Shaft sideShaft side

Beam entrance90º mirrorBeam entrance90º mirror

Beam splitter 50/50Beam splitter 50/50

Prism 30º bendPrism 30º bend


Beam monitorBeam monitor

Beam splitter 99/1Beam splitter 99/1Beam splitter 50/50Beam splitter 50/50


Muon side beam entranceMuon side beam entrance


Beam transport on TPC end plates (2)Beam transport on TPC end plates (2)

Muon sideMuon side

Beam entrance90º mirrorBeam entrance90º mirror




Beam monitorBeam monitor

Beam splitter 99/1Beam splitter 99/1Beam splitter 50/50Beam splitter 50/50


Muon arm side beam transport

Muon arm side beam transport

limited space between TPC and space frame move beam transport 10º from vertical plane adds 2 mirrors on shaft side + modifies beam transport on muon side

attach 50 mm pipe on outside of TPC permanently

special prismspecial prism

”knee” in beam transport on shaft side”knee” in beam transport on shaft side

”standard” prism”standard” prism

Muon sideMuon side

Shaft sideShaft side

We are currently considering to move back into the vertical planeWe are currently considering to move back into the vertical plane


Design in progress on opto-mechanical supports on end-plates (copy/modify STAR systems):

Optics on TPC end platesOptics on TPC end plates

Prism holder

Construction foreseen in NBI workshop

Laserbeam

Market survey on optical components for end-plates ongoing

Piezo-electric adjustment system from New Focus on order


Mirror adjustersMirror adjusters

Based on commercial piezo solution 3 fully adjustable mirrors per half-TPC

Ethernet interface


Laser rod with mirrorsLaser rod with mirrors


Mirror support ringsMirror support rings

All rings have been produced at NBI


Micro-mirror z positionsMicro-mirror z positions

(a)

(b) (b)

(b)

(a)

(a)

4 micro-mirrors per rod, at about (0, 1/3, 2/3, 1) length vary z positions slightly between odd (a) and even (b) rods


Alignment by Poisson spotAlignment by Poisson spot

Wide laser beam Ball or discScreen

Camerad

= 266 nm


Operational aspectsOperational aspects

Sensors and remote controls:

Remote setup and monitoring of laser CCD cameras for beam positioning: entrance mirrors on end plates end points on end plates end of laser rods Remote beam manipulation: 4 mirrors in laser hut 1 entrance mirror on each end plateData taking:

Test + special calibration runs: trigger from laser trigger laser ( several μs @ 10 Hz) Normal physics runs: low rate trigger from laser


Stability of laser and beamsStability of laser and beams

Design with micro-mirrors laser ray positions determined by the mirror positions and angles, not by the main laser beam or movable optics.

Mechanical stability of the TPC is good enough for precise (100 m) relative measurements once the TPC is installed.

During construction and installation, the TPC will undergo stresses due to handling (rotation) and change of loads (ROCs, cables etc).

’Absolute’ positions must refer to: TPC end plates, ROCs and Central Electrode.


Construction tolerances and alignment accuracy (1)


What is known precisely and ’absolutely’ during construction? (100-150 m)

pad plane z and wire z and x/y position central electrode z position

Well measured relative to each other (100-150 m, 0.05 mrad): internal dimensions and angles in micro-mirror bundles micro-mirror bundles in support rings bundle support rings in uninstalled rods

Less well measured or prone to move during handling (500 m, 0.2 mrad):

rod positions relative to ROCs, central electrode and ALICE x,y,z




’Internal alignment’ and iterations (offline analysis) : electrons from central electrode ’absolute’ z electrons from ROC pad plane and wires ’absolute’ z, x/y laser tracks close to outer rods good relative alignment laser tracks are straight lines iterate to best ’absolute’ positions of laser rays track time variations

Additional alignment relative to end plates with horizontal and loaded TPC (100-200 m, 0.05 mrad):

measure rod / micro-mirror bundle positions by survey through rods (fiducial marks useful) measure some beams near inner cylinder with HeNe laser after rod installation


Status and TestsStatus and Tests

Laser lab at NBI Micro-mirror production in Moscow Tests of micro-mirrors at NBI Status of other components


Laser lab at NBILaser lab at NBI

power supply

1064 nm laser

doubler

532 nm

quadrupler

266 nm

expandingtelescope

amplifier

rod with micro-mirrors

CCD camera


Reflected 1 mm beamReflected 1 mm beam

FWHM=0.93mm

z=31cm z=200cm

FWHM=0.95mm

pure Fresnel diffraction


Reflected 1 mm beams (2)Reflected 1 mm beams (2)16 cm

47 cm

FWHM=1.00mm

1.17mm 0.93mm

19 cm

1.01mm

23 cm

1.10mm

31 cm

0.93mm

100cm

150cm

0.79mm

200cm

0.95mm

z=250 cm

1.14mm

beamdivergence0.35 mrad

Fresneldiffraction

Measured


Micro-mirror productionMicro-mirror production

1 mm quartz fibrescut at 45º, polished, coated7 micro-mirrors/bundle

All 60 bundles produced and delivered in September 2002, but problems with surface quality on some mirrors and mechanical precision on some cups preliminary: 46 accepted based on surface quality most of these will be accepted after being

mechanically improved at NBI

additional 30 bundles almost ready in Moscow

reflecting surfaces

brass cup

mechanical reference surface

Micromirror bundle


Angles measurements (1)Angles measurements (1)

and angles of all micromirror faces measured by goniometer in Moscow

0.0014 (5 arc sec)


Angles measurement (2)Angles measurement (2)

Re-calculation of angles to take into account offset centres of 7 mirrors

systematics in re-calculation still to be understood


Angles measurement (3)Angles measurement (3)

However: reference surface not good bundle not fixed to support in reproducible way

only relative angles any good from this measurement

Reference surface has beenturned off in NBI workshop toprovide good surface


Mirror surfaces (1)Mirror surfaces (1)

Looked at allmirror reflectionsafter 2.5 m.

Example:bundle 18+19


Mirror surfaces (2)Mirror surfaces (2)Analysed allmirror reflectionprofilesafter 2.5 m.

Example:bundle 18+19

Rejected badreflectivities andimage shapes.

Good mirrorsgenerally havequite uniformreflectivity


Mirror reflectancesMirror reflectances

Acceptance level: 150 (arbitrary units)

Preliminary accepted bundles (based on reflectivity and image quality): 46 bundles out of 61 received

Amplitudes of profiles on previous slide:

Micro-mirror number


Angles measurements @ NBI (1)


All mirror angles have been re-measuredat NBI, using laser beam setup.

Estimated precision: 0.5 mrad (2 arc min) 0.5 mrad (2 arc min)







Mean = -0.08Sigma = 0.51

Mean = -0.29Sigma = 0.94


Linear measurements @ NBI

Linear measurements @ NBI

L

Mean = -0.23 mmSigma = 0.57 mm


Rod gluingRod gluing

1. Drill holes in short rods2. Mount mirror bundles in support rings.

3. Glue mirror support rings onto short rods. Theta alignment guaranteed by jig + machined surface

4. Glue short rods into full length rods. Phi alignment adjusted during gluing

5. Measurements on final rod possible before installation.

Foreseen for February-March at CERN.


Production status and installation schedule

Production status and installation schedule

Notes and presentations: http://www.nbi.dk/~borge/tpclaser/

Rod system: Micro-mirror bundles: ready ~1 Feb 2003 Mirror support rings produced Mirror testing: ongoing, fall 2002 + beginning 2003 Rod production at CERN: spring 2003

Optics system: Principle design: done Detailed design: spring 2003 Production and installation: mid 2003 - spring 2004

Commissioning: Together with TPC chambers: 2nd half 2004 + 2005

Integration: Principle design: done Install laser in UX25: 2005 + 2006

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Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI1 TPC Laser system Functions of the...

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