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The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 1
The Gemini MCAO System
Andy Foster
Observatory Sciences Ltd
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 2
Adaptive Optics - The Movie
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 3
Classical AO Comparison
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 4
The plague of Classical AO…Limited 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.
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 5
The plague of Classical AO…Sky 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 AO…The Cone Effect
90 k
m
“Missing” Data
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The Solution - MCAOTelescope
DM1 DM2
Turb. Layers#2 #1
Atmosphere
WFS
UP
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 8
MCAO & the Cone Effect
90 k
m
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 9
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)
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 10
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 PPC’s
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 11
A
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
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270
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oard
OM
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Control LAN
Time bus
To servo motor electronics
To switches, relays, DC
motors
To TT mirrors
Ban
com
635
tim
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oard
MV
ME
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oard
XY
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+ 4
XIP
VM
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Synchro bus
From sensors
OM
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OM
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OM
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MCAOBTO/LLT
VME
BDSS
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 14
BTO/LLT EPICS Additions
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) 15
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
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 16
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 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)
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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 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) 18
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.
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 19
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
DMs
TTM
LGS WFS
NGS source simulator
LGS source simulatorScience ADC
BeamsplitterDiagnostic WFSNGS
WFS
LGS zoom correctorNGSADC
shutters
The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 22
AOM: Main Engineering Screen