TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 1

Status of laser systemStatus of laser system

TPC meeting, CERN, 29-30 April 2002B.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, 29-30 April 2002 Børge Svane Nielsen, NBI 2

TPC Laser principleTPC Laser principle

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 3

Laser tracks in TPCLaser tracks in TPC

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 4

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

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 5

Laser rod with mirrorsLaser rod with mirrorsdrawing shown in December 2001

New: Alu ring design changed & mirror support integrated with rings

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 6

Mirror support ringsMirror support rings

New: mirror support integrated with Alu rings:

Prototype produced at NBI

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 7

Rod gluingRod gluing

normal gas rod Alu ring:

normal gas rod macrolon piece:

mirror support ring:

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 8

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

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 9

Micro-mirror z positions (2)Micro-mirror z positions (2)

108 rods 1415 mm = 210 mm

24 rods 415 mm = 60 mm

24 rods 615 mm = 90 mm

12 rods 815 mm = 120 mm

12 rods 1015 mm = 150 mm

120 rods 1415 mm = 210 mm

24 rods 1215 mm = 180 mm

12 normal gas rods:

12 laser rods(full TPC):

Suggestion:All mirror support rings glued to short rods and6 long rods at NBI. Full rods glued at CERN.

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 10

New muon arm side beam transport

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 prismnew placement

alternatives

special prism

beam transport as foreseen

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 11

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

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 12

Reflected 1 mm beamReflected 1 mm beam

FWHM=.93mm

z=31cm z=200cm

FWHM=.95mm

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 13

Reflected 1 mm beams (2)Reflected 1 mm beams (2)z=13 cm 16 cm

47 cm

1.00mmFWHM=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

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 14

Preliminary HV testsPreliminary HV tests

200 M 10200 Mtotal L=2.10 m

70-80 kV40 A @ 80 kV

in air

laser off/on: no change in current (1 A)

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 15

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, 29-30 April 2002 Børge Svane Nielsen, NBI 16

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.

TPC meeting, CERN, 29-30 April 2002 Børge Svane Nielsen, NBI 17

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