TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI1 Status of laser system TPC meeting, CERN, April 2002 B.S.Nielsen, J. Westergaard Niels Bohr Institute  Micro-mirror production status  New support of micro-mirrors in rods  Micro-mirror z positions  New beam transport to muon arm side  NBI lab tests: 1 mm beam profiles preliminary high voltage tests  Absolute versus relative calibrations

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI2 TPC Laser principle

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI3 Laser tracks in TPC

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI4 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

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI5 Laser rod with mirrors drawing shown in December 2001 New: Alu ring design changed & mirror support integrated with rings 

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI6 Mirror support rings New: mirror support integrated with Alu rings: Prototype produced at NBI

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI7 Rod gluing normal gas rod Alu ring: normal gas rod macrolon piece: mirror support ring:

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI8 Micro-mirror z positions (1)  4 micro-mirrors per rod, at about (0, 1/3, 2/3, 1) length  vary z positions slightly between odd/even rod Principle of choosing z positions: Normal gas rod consists of sections:  mm with alu rings inbetween. In laser rod:  cut first and last section in two and insert laser ring  replace 2 normal rings with laser rings in odd rods  cut 2 middle sections and insert laser rings in even rods

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI9 Micro-mirror z positions (2) 108 rods14  15 mm = 210 mm 24 rods4  15 mm = 60 mm 24 rods6  15 mm = 90 mm 12 rods8  15 mm = 120 mm 12 rods10  15 mm = 150 mm 120 rods14  15 mm = 210 mm 24 rods12  15 mm = 180 mm 12 normal gas rods: 12 laser rods (full TPC): Suggestion: All mirror support rings glued to short rods and 6 long rods at NBI. Full rods glued at CERN.

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI10 New muon arm side beam transport possible new layout limited space between TPC and space frame  move beam transport 10º from vertical plane adds 2 mirrors on sharf side + modifies beam transport on muon side hope to attach 50 mm pipe on outside of TPC permanently special prism new placement alternatives special prism beam transport as foreseen

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI11 Laser lab at NBI power supply 1064 nm laser doubler  532 nm quadrupler  266 nm expanding telescope amplifier rod with micro-mirrors CCD camera

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI12 Reflected 1 mm beam FWHM=.93mm z=31cm z=200cm FWHM=.95mm

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI13 Reflected 1 mm beams (2) z=13 cm16 cm 47 cm 1.00mmFWHM=1.00mm 1.17mm 0.93mm 19 cm 1.01mm 23 cm 1.10mm 31 cm 0.93mm 100cm150cm 0.79mm 200cm 0.95mm

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI14 Preliminary HV tests 200 M  10  200 M  total L=2.10 m kV 40  80 kV in air laser off/on: no change in current (  1  A)

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI15 Laser system objectives (P. Glässel) 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 meeting, CERN, April 2002Børge Svane Nielsen, NBI16 Stability of laser and beams We are trying to assure the best possible mechanical stability in the construction and to make position measurements during installation. But: we cannot assure laser system position stability better than the tolerances and movements of the support structure (rods and cylinders). System with micro-mirrors  laser ray positions determined by the mirror positions and angles, not by the main laser beam. Mechanical stability of the TPC is good enough for precise (100  m) relative measurements once the TPC is installed. During installation, the TPC will undergo stresses due to handling (turning on end) and change of loads (ROCs, cables etc). ’Absolute’ positions must refer to something that it stable or measured relative to something else well-known: ROCs, central electrode... ? This should make the system better than most previous ones.

TPC meeting, CERN, April 2002Børge Svane Nielsen, NBI17 How obtain ’absolute’ positions? What is known precisely and ’absolutely’? (   m ?)  central electrode z position  pad plane z and gating wire z and x/y position  special effort: measure beams near inner cylinder for beams close to end-plate with TPC in horizontal position before installation of IROCs Well measured relative to each other (  100  m, 0.05 mrad):  internal angles in micro-mirror bundles  micro-mirror bundles in support rings  bundle support rings in uninstalled rods Probably needs ’internal alignment’ and iterations:  precise position and angles of beams far from end-plates  everything that may move due to twists of cylinders, rods etc. Less well measured or prone to move (  500  m, 0.2 mrad):  rod positions relative to ROCs, central electrode and ALICE x,y,z