tpc laser system

Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 1

TPC Laser systemTPC Laser system

Functions of the system Basics of the design Design updates since February TB Lab tests at NBI Construction tolerances and alignment Production status and installation

ALICE Technical Board, CERN, 14 May 2002Børge S. Nielsen, Jørn Westergaard and J.J. Gaardhøje

Niels Bohr Institute

A. Lebedev, Brookhaven National Laboratory


Laser system objectives(P. Glässel, LHCC review)

• 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, = 25 mm


Beam pattern inside TPCBeam pattern inside TPC

Radial beamsStratetic sector boundary crossingsAvoid laser beam crossings

336 laser tracks in full TPC


Laser beam transport to TPC

Laser beam transport to TPC

Shaft side beam

Muon side beam

Laser beams


New muon arm side beam transport

New muon arm side beam transport

new layout

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

hope to attach 50 mm pipe on outside of TPC permanently

new placement

beam transport as foreseen earlier

special prism


Beam transport on TPC end plates

Beam transport on TPC end plates

Muon sideMuon side

Beam entrance90º mirror

Beam splitter 50/50

Prism 30º bend

Beam splitter 33/67

Beam monitor

Beam splitter 99/1Beam splitter 50/50


Optics on TPC end platesOptics on TPC end plates

Example of optics box on TPC end plate

Prism box used in STAR


Micro-mirror productionMicro-mirror production

A.Ridiger, Moscow: all fibres cut, polished, coated and tested 43 of 60 mirror bundles produced angle measurements about to start

micro-mirror bundle

brass cup

protection cap

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


Laser rod with mirrorsLaser rod with mirrorsdrawing shown in February

New: Alu ring design changed & mirror support integrated with rings


Mirror support ringsMirror support rings

New mirror support integrated with Alu rings:

Prototype 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


OperationsOperations

Sensors and remote controls: Laser setup and monitoring by RS 232 CCD cameras for beam positioning: entrance mirrors on end plates end points on end plates end of laser rods Beam manipulation: few mirrors in laser hut entrance mirrors on end plates

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


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=.93mm

z=31cm z=200cm

FWHM=.95mm


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


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 (dedicated effort) (100-200 m, 0.05 mrad):

measure rod / micro-mirror bundle positions by special survey through rods (fiducial marks useful) measure some beams near inner cylinder for beams close to end-plate through holes for IROCs


Production status and installation schedule

Production status and installation schedule

Draft note: http://www.nbi.dk/~borge/tpclaser/

Rod system: Micro-mirror bundles in production Mirror support rings designed, needs final approval from TA2 Ring production, mirror installation: summer 2002 Rod production at CERN: fall 2002

Optics system: Principle design: done Detailed design: summer/autumn 2002 Production and installation: 2nd half 2003 + 2004

Commissioning: Together with TPC chambers

tpc laser system

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