TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 1 Status of laser system TPC meeting, CERN, 29-30 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
Status of laser system. 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. - PowerPoint PPT Presentation
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Micro-mirror z positions (1)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: 180+10210+180 mmwith 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
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
Stability of laser and beamsStability 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 measuredrelative to something else well-known: ROCs, central electrode... ?
This should make the system better than most previous ones.
How obtain ’absolute’ positions?How obtain ’absolute’ positions?
What is known precisely and ’absolutely’? (100-200 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