The Gemini MCAO System

1. The Gemini MCAO System Andy Foster Observatory Sciences Ltd

2. Adaptive Optics - The Movie

3. Classical AO Comparison

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.

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”.

6. 90 km “Missing” Data The plague of Classical AO…The Cone Effect

7. The Solution - MCAO Turb. Layers Telescope WFS #2 #1 DM2 DM1 Atmosphere UP

8. MCAO & the Cone Effect 90 km

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)

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

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

12. BTO/LLT: Main Engineering Screen

13. 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 switches, relays, DC motors To servo motor electronics To TT mirrors From sensors

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

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

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)

17. 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.

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.

19. BDSS: Main Engineering Screen

20. BDSS: Simulated Far Field and Phase Retrieval Plots Skycat Display of Simulated Far Field Phase Retrieval Plots

21. LGS source simulator NGS source simulator Science ADC DMs shutters TTM Beamsplitter Diagnostic WFS NGS WFS LGS WFS NGS ADC LGS zoom corrector Adaptive Optics Module

22. AOM: Main Engineering Screen