NBI

TPC laser calibration system

Børge Svane Nielsen

Niels Bohr Institute

GSI, 10 December 2001

Table of Contents

System Goals 1

Design of laser system: from laser to narrow beams 2

Precision: production, installation and alignment 10

Production, installation and alignment 11

NBI System Goals

System Goals

Planned use of laser calibration system:

– Electronics testing– Sector alignment– Drift velocity measurement– Drift distortions: temperature effects, space charge and ExB effects

Goals for laser track layout and precision:

– 1 mm UV laser beams through most of TPC volume– 1–5 mip equivalent ionization– cross sector boundaries appropriately– radial beams at different z and

�

– production + installation precision: � 10-20 mm @ 2-3 m– alignment precision: � 0.2 mm

Collaboration:

– Alexei Lebedev (STAR) can collaborate part-time– will probably supply micro-mirrors from Moscow

10 December 2001 TPC laser calibration system-1 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Design of laser system: from laser to narrowbeams

Laser hut and beam transport to TPC end-plates.

10 December 2001 TPC laser calibration system-2 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

10 December 2001 TPC laser calibration system-3 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Beam transport on TPC end-plates, Shaft side

10 December 2001 TPC laser calibration system-4 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Beam transport on TPC end-plates, Muon side

10 December 2001 TPC laser calibration system-5 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Laser rods.

10 December 2001 TPC laser calibration system-6 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Suggested beam pattern R-�

Aim for � radial beams and strategic sector boundary crossings

10 December 2001 TPC laser calibration system-7 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Beam pattern R-Z:

– Current thinking: 4 mirror positions in Z– Large span and � uniform distribution in Z– Avoid crossing laser beams in TPC volume

��� 2 or more different mirror Z distributions

10 December 2001 TPC laser calibration system-8 Børge Svane Nielsen, NBI

NBI Design of laser system: from laser to narrow beams

Issues relating to TPC design:

– Placement of beam transport pipe between TPC and space frame– Laser rods not back-to-back– High voltage rod moved to 5 o’clock position– Space for optics boxes on TPC end-plates– 50 mm pipes at � 120 mm above TPC end-plates– 44 mm laser rods– � 15 mm optical holes through central electrode ring– specify type(s) of glue and materials

Missing design issues:

– Details in rod mechanics and micro-mirror support– Quartz window in central electrode hole?– Details in optics for beam transport (e.g. polarisation issues)– Details in beam monitoring and steering– One or two lasers?

10 December 2001 TPC laser calibration system-9 Børge Svane Nielsen, NBI

NBI Precision: production, installation and alignment

Precision: production, installation andalignment

Final alignment precision aim: 200–300 � m space points, i.e.�x,�

y,�

z (mirrors) � 200 � m� �,�

(track angles) � 0.1 mrad

We are aiming at achieving this is 2 steps:

Error sources in beam positions relative to nominal:– Mirror bundle production– Installation in laser rods– Installation of laser rods in TPC�

x,�

y,�

z (mirrors) � 200 � m� �,�

(mirrors) � � �

Error sources in measured beam positions:– Measurement of mirrors in bundles:�

x,�

y,�

z � 100 � m� �

,� � 0.05 mrad

– Measurement of mirror bundles in rods:�x,�

y,�

z � 100 � m� �

,� � 0.05 mrad

– Measurements of assembled rods:�x,�

y,�

z � 100 � m� �

,� � 0.1 mrad

– Measurements of installed rods in TPC:�x,�

y,�

z � 200 � m� � 0.1 mrad (OK – rods do not bend)� � � 0.1 mrad (tough!!)– Movements of outer cylinder, laser rods and mirror holders:

needs more studies

10 December 2001 TPC laser calibration system-10 Børge Svane Nielsen, NBI

NBI Production, installation and alignment

Production, installation and alignment

Micro-mirror and rod production:

– Micro-mirror production and measurement probably as for STAR– Assembly and measurement of rod pieces at NBI– Full rod assembly and measurement at CERN

Issues relating to TPC assembly:

– Rod installation: can we assure�

mechanically to ��� or better?– Alignment measurements on assembled TPC, before service

support wheel: look through rods from end-plate to end-plate

– Measure some spots from HeNe laser inside TPC before chambers?To be studied and put into schedule: time and access

Optics and laser control and monitoring:

– Detailed design and production in parallel with rod production– Production and assembly at NBI– Installation and alignment on TPC end-plates– Laser hut and beam transport in surface test area– Laser hut and beam transport in ALICE

10 December 2001 TPC laser calibration system-11 Børge Svane Nielsen, NBI