Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI1 TPC Laser system Functions of the...
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Transcript of Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI1 TPC Laser system Functions of the...
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 2
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 3
TPC Laser principleTPC Laser principle
20-40 μJ/pulse, = 1 mm
266 nm, 100 mJ/pulse, = 25 mm
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 4
Beam pattern inside TPCBeam pattern inside TPC
Radial beamsStratetic sector boundary crossingsAvoid laser beam crossings
336 laser tracks in full TPC
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 5
Laser beam transport to TPC
Laser beam transport to TPC
Shaft side beam
Muon side beam
Laser beams
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 6
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 7
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 8
Optics on TPC end platesOptics on TPC end plates
Example of optics box on TPC end plate
Prism box used in STAR
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 9
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 10
Laser rod with mirrorsLaser rod with mirrorsdrawing shown in February
New: Alu ring design changed & mirror support integrated with rings
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 11
Mirror support ringsMirror support rings
New mirror support integrated with Alu rings:
Prototype produced at NBI
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 12
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 13
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 14
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 15
Reflected 1 mm beamReflected 1 mm beam
FWHM=.93mm
z=31cm z=200cm
FWHM=.95mm
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 16
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 17
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.
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 18
Construction tolerances and alignment accuracy (1)
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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 19
Construction tolerances and alignment accuracy (2)
Construction tolerances and alignment accuracy (2)
’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
Technical Board, CERN, 14 May 2002 Børge Svane Nielsen, NBI 20
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