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.

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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”.

The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 6

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

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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 PPC’s

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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

The Gemini MCAO System (EPICS Meeting, SLAC, April 2005) 13

BTO/LLT VME architecture

MV

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270

0 –

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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

e b

oard

MV

ME

270

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U b

oard

XY

CO

M 9

660

+ 4

XIP

VM

IVM

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88 R

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oard

Synchro bus

From sensors

OM

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OM

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OM

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MCAOBTO/LLT

VME

BDSS

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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

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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 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.

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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

DMs

TTM

LGS WFS

NGS source simulator

LGS source simulatorScience ADC

BeamsplitterDiagnostic WFSNGS

WFS

LGS zoom correctorNGSADC

shutters

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AOM: Main Engineering Screen