The Gemini MCAO System

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The Gemini MCAO System

• Andy Foster
• Observatory Sciences Ltd

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Adaptive Optics - The Movie
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Classical AO Comparison
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The plague of Classical AOLimited Field of View

• Wavefront sensors measure perturbations along
  line of sight to guide star.
• These will differ along line of sight to the
  science target.
• See images below taken 20 arcseconds apart.

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The plague of Classical AOSky Coverage

• Need bright stars close to science target for AO.
• Only 5 of the sky is accessible.
• Use Laser Guide Stars (LGS) to get round this.
  Fluorescence of sodium atoms at 90/100km.
• But not without problems. Cannot determine
  Tip/Tilt information from an LGS. This is where
  most of the phase correction comes from.
• Finite height of LGS leads to The Cone Effect.

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The plague of Classical AOThe Cone Effect
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The Solution - MCAO
Telescope
Turb. Layers
WFS
2
1
DM2
DM1
Atmosphere
UP
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MCAO the Cone Effect
90 km
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The MCAO Subsystems

• MCAO contains the following subsystems
• The Laser System (LS)
• The Real-Time Controller (RTC)
• The Safe Aircraft Localization and Satellite
  Acquisition System (SALSA)
• The Beam Transfer Optics and Laser Launch
  Telescope Systems (BTO/LLT)
• The Beam Diagnostics Sensor System (BDSS)
• The Adaptive Optics Module (AOM)

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The BTO/LLT Subsystem

• Control System designed and developed by OSL.
  Commissioning this week!
• The BTO/LLT subsystem is responsible for taking
  the laser beams from the centre section of the
  telescope and transferring them up the telescope
  truss, across the secondary vanes and then
  launching them from behind the secondary mirror.
• VME based
• EPICS 3.13.9 with the Gemini extensions
• vxWorks 5.4.2 (Tornado 2.0.2)
• Two MVME-2700 PPCs

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Laser path

• Five 14-W beams
• Laser System location
• On center section (A)
• On-axis LLT

A
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BTO/LLT Main Engineering Screen
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BTO/LLT VME architecture
BDSS
Synchro bus
Time bus
Control LAN
OMS58-8S motor controller
OMS58-8S motor controller
OMS58-8S motor controller
OMS58-4S motor controller
MVME 2700 CPU board
MVME 2700 CPU board
VMIVME5588 RM board
Bancom 635 time board
XYCOM 9660 4 XIP
MCAO BTO/LLT VME
To servo motor electronics
To switches, relays, DC motors
To TT mirrors
From sensors
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BTO/LLT EPICS Additions

• EPICS driver for Xycom-9660 carrier board
  (following Andrew Johnsons drvIpac approach)
• Device driver support for XIP-2440 digital
  input module
• bi, mbbi, mbbiDirect records, interrupt support
• Device driver support for XIP-2445 digital
  output module
• bo, mbbo, mbboDirect records
• Device driver support for XIP-5320 analog input
  module
• ai, waveform records
• supports on-board calibration through a vxWorks
  task every 30 minutes
• Device driver support for XIP-5230 analog
  output module
• ao record
• Drivers can be compiled without EPICS
• ao driver is used to drive piezo-electric
  actuators at up to 1 kHz for FSA control

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BTO/LLT EPICS Additions

• Velocity and acceleration of tip and tilt axis
  motors must provide smooth, linear travel between
  mirror positions
• Multi-axis linear coordinated moves are
  supported by OMS 58 motion controller
• As far as we could tell, this feature is not
  supported by any current EPICS records, so
• Coordinated Motion Record developed by Gemini to
  handle multiple axis moves

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The Beam Diagnostics Sensor System

• The role of the BDSS is to provide feedback to
  the truss pointing and centering arrays to
  maintain alignment of the laser beams and to keep
  the FSA within its dynamic range.
• Uses two commercial (Pixelfly) CCD cameras to
  image the near and far fields of the laser
• Measures centroids of spots and calculates
  offsets from pre-determined positions
• Corrections applied to truss pointing and
  centering mirrors by BTO
• Provides measurements of the beam quality of the
  laser at the top-end
• times diffraction limit (1 for a Gaussian beam)

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The Beam Diagnostic Sensor System

• Runs on a Linux (Red Hat 9.0) target
• Running EPICS 3.14.5 with Gemini extensions
• Use ESOs Skycat tool to display images
• Interface to cameras is through PCIbus, came with
  Linux driver
• Wrote a SCAM (Simulated Camera) driver which
  manipulates memory buffers to test without
  cameras
• Using a 2.66 GHz Pentium 4 (512 MB RAM), can read
  out both cameras (1390 x 1024 pixels) at 8.6 Hz.

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The Beam Diagnostics Sensor System Software
Design

• epicsThreadCreate called to create tasks which
  analyse and manipulate the image data. This is
  done through a genSub INIT routine at iocInit.
• Interface between these tasks and EPICS records
  which hold the calculated offset values is
  through a library which accesses a protected
  memory area.
• Standard EPICS records used to control functions
  of the cameras such as
• Binning
• Exposure time
• Reading the temperature
• Commands are sent to the BDSS through standard
  Gemini CAD records.
• Being able to use EPICS under Linux has allowed
  us to fully integrate this system with the rest
  of the Gemini Control System. This is very
  positive and we have seen no major problems using
  a Linux target.

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BDSS Main Engineering Screen
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BDSS Simulated Far Field and Phase Retrieval
Plots
Skycat Display of Simulated Far Field
Phase Retrieval Plots
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Adaptive Optics Module
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AOM Main Engineering Screen