Interaction Region Optical and Optomechanical Design

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?? Interaction Region Optical andOptomechanical
Design

• Ken Skulina/LLNL
• Snowmass 2001 The Future of Particle Physics
• Snowmass CO, 6 July 2001

Contributors David Asner, Steve Boege, Paul
Bloom, John Crane, Jim Early, Jeff Gronberg,
Scott Lerner, Steve Mills, Lynn Seppala
This work was performed under the auspices of the
U.S. Department of Energy by the University of
California, Lawrence Livermore National
Laboratory under Contract No. W-7405-Eng-48.
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Agenda

• Introduction to the optical system
• Optomechanical packaging into the Interaction
  region
• Engineering issues
• The conceptual design is a snapshot in time. It
  is meant to help further detailed design and
  define interfaces

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Lets understand where we are in the system
Ti-sapphire oscillator
Grating Stretcher
OPA Pre-amp
Mercury Amplifiers
Grating Compressor
EO switch

Beam Steering and Transport
Controls Timing Diagnostics Accelerator Interface
Detector
Interaction Region
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All Laser light generation occurs remotely from
the IR


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The laser light and charged particles collide at
15 mrad
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Optical Design Requirements

• Two foci, separated by 1 cm.
• 1 times diffraction limited.
• Ability to handle high peak power laser light.
• Near co-linear laser and electron beam
  propagation.
• Spot size 10 ?m diameter.
• Pathlength control on return leg.
• Ability to rotate polarization on return leg.
• These requirements are met using
• Two Schwarzchild focusing systems.
• All reflective optics (except waveplate).

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The interaction region is at the center of all
detectors
Magnet
Hadron calorimeter

EM calorimeter
Muon chambers
Tracker
IR (including vertex detector)
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The ?? IR is surrounded by other detector
subsystems
s
Exploded views help determine physical
interfaces and assembly methods
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We Will Be Packaging the Following Optical Train
Optics only
Optics beampath
Side view of optics and beampath
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Several competing requirements for the focusing
optics must be met

• Laser beam must be nearly co-linear with the
  electron beam
• Electron beam must pass through the final
  focusing optic
• Conversion efficiency goal determines photon
  number density
• laser pulse energy then proportional to spot size
  (f?)2
• want minimum f on focusing optic
• Laser beam and electrons must simultaneously be
  at conversion point
• Length of laser pulse (2ps) must be similar to
  electron pulse
• Depth of field (2?f) as long as laser pulse
  gives minimum f
• Optimum f for optics f7

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The first packaging task is to accommodate the
electron beam paths
Electron beams go through The focusing optics
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A central hole in the two end mirrors allows
charged particle and background transport

• Final focusing optic must be closely aligned to
  the electron beams
• beam must pass through center of optic
• Hole in primary optic for electron beams also
  allows passage of most of the background
  particles

Incoming electron beam
Exiting electron beam
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A wireframe model lets us see the laser light and
electron beam paths.
Focusing optic with Central hole
Electron beam entrance and exit
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2D IR Region Layout (incoming leg)
1 micron laser transport
IR beampipe
mask
Vacuum enclosure(s)
QD0
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2D IR Region Layout (reflected leg)
Silicon plate detectors
QD0
Vacuum enclosure
mask
beampipe
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Polarization options

• The polarization of the laser beams can be
  controlled to allow either parallel of crossed
  polarization in the ?? collisions
• Straight reflection of the linear polarized laser
  beam to interact with the second electron beam
  results in parallel polarizations
• For crossed polarization a waveplate is placed in
  the beampath of the reflected laser beam
• Insertion of a waveplate is a quick, remotely
  controlled operation.

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Modeled Optical Performance Figure of Merit
Worst case P-V wavefront error at focus is ?/4
(?1053nm)
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Several features are unique to a ?? collider IR

• Cylindrical carbon fiber outer tube
• Vacuum boundary with transition from thick
  cylinder to thin beampipe.
• Sections of strongback for optical support
• Thermal Management

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Finite Element Analysis shows a benign mechanical
environment
Max Static sag 50 microns Static sag at focus
25 microns 1st fund freq 70Hz
Anticipated vibration lt .05 ?m rms at focus _at_
10-10 g2/Hz 1-200 Hz
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Optical Train-IR buildup contained within the
carbon fiber-honeycomb tube
The design intent was to have the ?? IR
self-contained (assembled and rough aligned)
within a low z tube.
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The entire carbon fiber tube is inserted on a
rail-pillow block system
Carbon fiber tube
rail
Pillow-block
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Thermal management

• Absorbed 1 micron light will be re-radiated.
• Use thermally stabilized optical strongbacks
• Use chill plates behind optical mounts.
• Constant temperature water (-0.1C) can supply
  this thermal control

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Current applications will be modified to use UHV
inchworm actuators
Waveplate rotation stage
Tip/tilt mirror stage

• A vendor has been identified that can deliver
  motor operation in a ultra-high vacuum, 3T
  environment

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Optomechanical Design Drivers/Requirements/Constra
ints
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The control system still needs to be designed

• Pointing and centering required
• Diagnostic for collision with electrons

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Conclusions

• Current Mercury Laser Technology can meet
  Gamma-Gamma collider needs.
• All major Interaction Region design requirements
  can be met.