Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI1 TPC 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 2003 Børge S. Nielsen, J.J. Gaardhøje, N. Lindegaard and Jørn Westergaard Niels Bohr Institute A. Lebedev, Brookhaven National Laboratory

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI2 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

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI3 TPC Laser principle μJ/pulse,  = 1 mm 266 nm, 100 mJ/pulse, 5 ns pulse,  = 25 mm

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI4 Beam pattern inside TPC Radial beams Stratetic sector boundary crossings Avoid laser beam crossings 8 ’layers’ of rays along z 336 laser tracks in full TPC 

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI5 Spectron Laser Systems (UK): model SL UPG Pulsed UV laser (Nd:YAG): 100 mJ / 5 ns 266 nm, max 10 Hz expanded beam  = 25 mm divergence < 0.35 mrad, pointing stability < 0.1 mrad remote controllable (RS-232) UV laser

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI6 Laser hut and laser beam transport (1)

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI7 Laser hut and laser beam transport (2)

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI8 Beam transport on TPC end plates (1) Shaft side Beam entrance 90º mirror Beam entrance 90º mirror Beam splitter 50/50 Prism 30º bend Beam splitter 33/67 Beam monitor Beam splitter 99/1 Beam splitter 50/50 Prism 30º bend Muon side beam entrance

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI9 Beam transport on TPC end plates (2) Muon side Beam entrance 90º mirror Beam entrance 90º mirror Beam splitter 50/50 Prism 30º bend Beam splitter 33/67 Beam monitor Beam splitter 99/1 Beam splitter 50/50

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI10 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 prism ”knee” in beam transport on shaft side ”standard” prism Muon side Shaft side We are currently considering to move back into the vertical plane

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI11 Design in progress on opto-mechanical supports on end-plates (copy/modify STAR systems): Optics on TPC end plates Prism holder Construction foreseen in NBI workshop Laser beam Market survey on optical components for end-plates ongoing Piezo-electric adjustment system from New Focus on order 

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI12 Mirror adjusters Based on commercial piezo solution  3 fully adjustable mirrors per half-TPC Ethernet interface

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI13 Laser rod with mirrors

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI14 Mirror support rings All rings have been produced at NBI

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI15 Micro-mirror z positions (a) (b) (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

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI16 Alignment by Poisson spot Wide laser beamBall or disc Screen Camera d = 266 nm

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI17 Operational 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 plate Data taking:  Test + special calibration runs: trigger from laser trigger laser (  several 10 Hz)  Normal physics runs: low rate trigger from laser

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI18 Stability 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.

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI19 Construction tolerances and alignment accuracy (1) What is known precisely and ’absolutely’ during construction? (   m)  pad plane z and wire z and x/y position  central electrode z position Well measured relative to each other (   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

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI20 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 (   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

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI21 Status and Tests  Laser lab at NBI  Micro-mirror production in Moscow  Tests of micro-mirrors at NBI  Status of other components

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI22 Laser lab at NBI power supply 1064 nm laser doubler  532 nm quadrupler  266 nm expanding telescope amplifier rod with micro-mirrors CCD camera

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI23 Reflected 1 mm beam FWHM=0.93mm z=31cm z=200cm FWHM=0.95mm pure Fresnel diffraction

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI24 Reflected 1 mm beams (2) 16 cm 47 cm FWHM=1.00mm 1.17mm0.93mm 19 cm 1.01mm 23 cm 1.10mm 31 cm 0.93mm 100cm 150cm 0.79mm 200cm 0.95mm z=250 cm 1.14mm beam divergence 0.35 mrad Fresnel diffraction Measured

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI25 Micro-mirror production 1 mm  quartz fibres cut at 45º, polished, coated 7 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

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI26 Angles measurements (1)  and  angles of all micromirror faces measured by goniometer in Moscow     (5 arc sec)

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI27 Angles measurement (2) Re-calculation of angles to take into account offset centres of 7 mirrors  systematics in re-calculation still to be understood

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI28 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 been turned off in NBI workshop to provide good surface

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI29 Mirror surfaces (1) Looked at all mirror reflections after 2.5 m. Example: bundle 18+19

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI30 Mirror surfaces (2) Analysed all mirror reflection profiles after 2.5 m. Example: bundle Rejected bad reflectivities and image shapes. Good mirrors generally have quite uniform reflectivity

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI31 Mirror 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

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI32 Angles NBI (1) All mirror angles have been re-measured at NBI, using laser beam setup. Estimated precision:   0.5 mrad (2 arc min)   0.5 mrad (2 arc min)

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI33 Angles NBI (2)

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI34 Angles NBI (3) Mean =  Sigma = 0.51  Mean =  Sigma = 0.94 

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI35 Linear NBI L Mean = mm Sigma = 0.57 mm

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI36 Rod gluing 1.Drill holes in short rods 2.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.

Laser Design Review, CERN, 27 Jan 2003Børge Svane Nielsen, NBI37 Production status and installation schedule Notes and presentations: Rod system: Micro-mirror bundles: ready ~1 Feb 2003 Mirror support rings produced Mirror testing: ongoing, fall beginning 2003 Rod production at CERN: spring 2003 Optics system: Principle design: done Detailed design: spring 2003 Production and installation: mid spring 2004 Commissioning: Together with TPC chambers: 2nd half Integration: Principle design: done Install laser in UX25: