Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI1 TPC 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 2002 Børge S. Nielsen, Jørn Westergaard and J.J. Gaardhøje Niels Bohr Institute A. Lebedev, Brookhaven National Laboratory

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI2 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 2002Børge Svane Nielsen, NBI3 TPC Laser principle μJ/pulse,  = 1 mm 266 nm, 100 mJ/pulse,  = 25 mm

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI4 Beam pattern inside TPC Radial beams Stratetic sector boundary crossings Avoid laser beam crossings 336 laser tracks in full TPC

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI5 Laser beam transport to TPC Shaft side beam Muon side beam Laser beams

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI6 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 2002Børge Svane Nielsen, NBI7 Beam transport on TPC end plates Muon side 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

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI8 Optics on TPC end plates Example of optics box on TPC end plate Prism box used in STAR

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI9 Micro-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 fibres cut at 45º, polished, coated 7 micro-mirrors/bundle

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI10 Laser rod with mirrors drawing shown in February New: Alu ring design changed & mirror support integrated with rings 

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI11 Mirror support rings New mirror support integrated with Alu rings: Prototype produced at NBI

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI12 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

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI13 Operations 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 10 Hz)  Normal physics runs: low rate trigger from laser

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI14 Laser lab at NBI power supply 1064 nm laser doubler  532 nm quadrupler  266 nm expanding telescope amplifier rod with micro-mirrors CCD camera

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI15 Reflected 1 mm beam FWHM=.93mm z=31cm z=200cm FWHM=.95mm

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI16 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

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI17 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.

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI18 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

Technical Board, CERN, 14 May 2002Børge Svane Nielsen, NBI19 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) (   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 2002Børge Svane Nielsen, NBI20 Production status and installation schedule Draft note: 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 Commissioning: Together with TPC chambers