Optical Anchor Interferometer Status: June, 2004

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Optical Anchor / Interferometer Status June, 2004

• Josef Frisch

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Concept (still just a cartoon)
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Interferometer

• Commercial unit manufactured by Zygo.
• Single axis purchased, expandable.
• Heterodyne interferometer
• Offset frequency set by RF acousto-optical cell
• Good immunity to optical noise
• Lambda / 2048 measurement
• Low data age allows easy feedback.
• Includes Laser, single axis interferometer,
  detector, cables, etc.

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Interferometer Specs

• 0.15nm 0.5ppb resolution
• No detailed noise specs
• Expect noise to be better for short timescales
• Performance likely limited materials drift
• Probably need vacuum transport
• Index change of windows with temperature
• Thermal expansion of supports
• Should be adequate for 1nm stability (relative to
  ground)

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Tasks

• Receive Laser (June 2004)
• Data acquisition software
• Simple test setup to verify basic operation
• Test setup for stability / noise
• Who guards the guardsmen?
• Feedback Software development
• Test single axis feedback system
• Purchase multi-axis system (6 or 12 axis)
• Install system at ATF
• Test multi-axis feedback

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Data Acquisition

• This is probably the most critical issue!
• Interferometer in VME format
• Plan to integrate with Vibration / ATF VME
  data-acquisition.
• Already have software platform for multi-axis
  feedback
• Requires significant infrastructure for operation
• VME crate, VME controller. Unix server.
• Software development also requires
• VxWorks development platform

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Testing

• Plan for Mike Hildrith to test system
• Has time and student.
• Physical infrastructure for testing probably not
  too difficult.
• What to do about DAQ
• Need VME crate controller (12K)
• Need host platform / software

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System testing software options (1)

• Use Vibration / ATF SLAC system
• Existing vibration system provides flexible
  multi-axis characterization and feedback
  capabilities
• Linda Hendrickson guesses end of summer to have
  data acquisition system for interferometer. (will
  have better estimate when manuals arrive)
• Additional manpower may speed this up (but
  ramp-up time)

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System testing software options (2)

• Mike Hildrith develops driver compatible with
  vibration system.
• Allows for easy future integration with other
  data acquisition.
• Would need to either purchase VxWorks development
  environment, or use the SLAC environment remotely.

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System testing software options (3)

• Develop completely independent platform for
  testing.
• Might be simpler for initial testing.
• Would need to re-do work to integrate with
  existing system, or re-do the very large amount
  of effort already applied to existing system.
• Interferometer hardware required for development,
  so this would delay driver development at SLAC

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Present DAQ system operation

• Realtime (vibration) feedback runs at 1KHz on
  private bus to DSP
• Vibration data (100KB/sec) from DSP -gt crate
  controller -gt ethernet -gt NFS
• Nanobpm data (10KB/sec) from crate controller -gt
  ethernet -gt EPICS
• Scopes independent.

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Changes for next generation

• Use PPC processor
• Feedback calculations in crate controller
• Need real time operation of crate controller
• Add interferometer support
• Looks similar to vibration sensors
• Optionally add PC with LabView for scope control.
  
• Use LabView to EPICS interface to centralize data
• Optionally replace Solaris NFS server with PC NFS
  server also running labview

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Future direction of software

• LabView
• Wide variety of hardware supported (in pc format)
• Poor support for VME or real time.
• EPICS
• Wide use in accelerator community
• Existing interface to real time system
• Difficult to learn
• Make it look like new LCLS system (VME/EPICS)?
• Some hardware only in VME
• Interferometer (best), 100Ms/s ADC (cheapest)
• Good crate density.
• Minimal system large and complex
• PC bus advantages
• Labview, variety of hardware, cheap processing /
  data storage.
• Poorly suited to real-time

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Other Tasks

• Interferometer support hardware
• Probably need vacuum transport lines
• Mount corner cubes to support frame / ground (in
  vacuum?)
• Temperature stabilization
• 1nm over 1M scale length is .0001 degree C.
• Support redesign for feedback
• Soft supports, Fast actuators

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Goals of Interferometer / optical anchor system

• Stabilize a test mass the NanoBPM support frame
• Can measure performance above 0.1Hz using STS-2
  seismometers.
• May need multiple seismometers to compare with
  ground !
• Need to understand beam based experiments.
• Can we compare 2 support frames with beam? (may
  be difficult to get 1nm given lever arm).
• 3 independently supported NanoBPMs?