The Gemini MCAO System
Andy Foster
Observatory Sciences Ltd
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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Adaptive Optics - The Movie
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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Classical AO Comparison
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The plague of Classical AO…
Limited Field of View
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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.
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The plague of Classical AO…
Sky Coverage
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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”.
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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90 km
The plague of Classical AO…
The Cone Effect
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
“Missing” Data
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The Solution - MCAO
Turb. Layers
#2
Telescope
#1
WFS
DM1
DM2
Atmosphere
UP
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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90 km
MCAO & the Cone Effect
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The MCAO Subsystems
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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)
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The BTO/LLT Subsystem
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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 PPC’s
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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Laser path
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Five 14-W beams
Laser System location:
– On center section (A)
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On-axis LLT
A
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
A
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BTO/LLT: Main Engineering Screen
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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BTO/LLT VME architecture
BDSS
Synchro bus
Time bus
To servo motor
electronics
To TT
mirrors
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
XYCOM 9660 + 4 XIP
OMS58-4S motor controller
OMS58-8S motor controller
OMS58-8S motor controller
OMS58-8S motor controller
VMIVME5588 RM board
Bancom 635 time board
MVME 2700 – CPU board
MVME 2700 – CPU board
Control LAN
From
sensors
MCAO
BTO/LLT
VME
To switches,
relays, DC
motors
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BTO/LLT EPICS Additions
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EPICS driver for Xycom-9660 carrier board (following Andrew
Johnson’s “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
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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BTO/LLT EPICS Additions
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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
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As far as we could tell, this feature is not
supported by any current EPICS records, so…
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Coordinated Motion Record developed by
Gemini to handle multiple axis moves
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The Beam Diagnostics Sensor
System
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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 it’s 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)
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The Beam Diagnostic Sensor
System
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Runs on a Linux (Red Hat 9.0) target
Running EPICS 3.14.5 with Gemini extensions
Use ESO’s 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.
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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The Beam Diagnostics Sensor
System – Software Design
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“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
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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.
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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BDSS: Main Engineering Screen
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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BDSS: Simulated Far Field and Phase
Retrieval Plots
Skycat Display of Simulated Far Field
Phase Retrieval Plots
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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Adaptive Optics Module
LGS source
Science ADC simulator
NGS source
simulator
DMs
shutters
TTM
Beamsplitter
NGS
WFS
NGS
ADC
Diagnostic WFS
LGS WFS
LGS zoom corrector
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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AOM: Main Engineering Screen
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005)
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