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Beyond Conventional Adaptive Optics Venezia 7-10 May 2001 The adaptive secondary mirror for the 6.5 conversion of the MMT Presented by A. Riccardi A. Riccardi.

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Presentation on theme: "Beyond Conventional Adaptive Optics Venezia 7-10 May 2001 The adaptive secondary mirror for the 6.5 conversion of the MMT Presented by A. Riccardi A. Riccardi."— Presentation transcript:

1 Beyond Conventional Adaptive Optics Venezia 7-10 May 2001 The adaptive secondary mirror for the 6.5 conversion of the MMT Presented by A. Riccardi A. Riccardi 1, G. Brusa 1, C. Del Vecchio 1, R. Biasi 2, M. Andrighettoni 2, D. Gallieni 3, F. Zocchi 4, M. Lloyd-Hart 5, F. Wildi 5, H. M. Martin 5 1 – Osservatorio Astrofisico di Arcetri, Firenze, Italy 2 – Microgate, Bolzano, Italy 3 – ADS, Lecco, Italy 4 – Media Lario, Lecco, Italy 5 – Steward Observatory, Tucson, AZ, U.S.A.

2 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 People (some of them) Osservatorio di Arcetri

3 Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Adaptive Secondary Concept WFS Sci. Camera DM Coll. TTM BS Conventional Secondary Adaptive Secondary Sci. Camera WFS Less warm surfaces K band: shorter exp. time (MLH, PASP) Adaptive Secondary

4 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Large stroke, no hysteresis 240mm P36 prototype 36 act. prototype ( =633nm) Astigmatism PtV=12  m

5 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 mirror diameter 642 mm mirror thickness 2 mm membrane in-plane restraint 336 moving magnet actuators nominal air gap ~ 40  m reference body 50 mm thick AL cold plate: actuators support & cooling (7 cooling channels) 24 absolute gap sensors fixed hexapod support frame & interface to Hexapod electronics cooled crates hub interfaces (power, signal & cooling) System Layout

6 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 MMT336 ASPHERIC SHELL Assembled unit Magnets 642mm diam. 2mm thick (12mm diam) Cap. sensor armatures (ref.plate)

7 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May crates 14 control boards each crate 8 channels controlled by each board (4DSP) capacitive sensor signal conditioning on the actuators (close to variable gap capacitor) Electronics – control system

8 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Resonances in control bw First 270 modes have res < 1kHz + local control Phase lag of 180deg for > res if low damping => unstable P30 “astigmatism” mode TF 37  m gap 115  m gap 37  m gap 115  m gap High damping (18Ns/m => 40  m gap) + local control PD increasing Damping: larger PM

9 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Control loop Commands from WFC - + DM k-th Curr. Driver + coil Capsens DSP of k-th channel 40kHz local loop DSP + Feed-forward + +

10 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Feed-forward matrix - zonal FF matrix (Cap. sensor readings)

11 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Feed-forward matrix - modal (Cap. sensor readings) Modal excitation: improved SNR

12 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 The FF matrix fitting

13 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Modal stiffness Act stiffness 0.2N/  m Local ctrl dominates FF dominates

14 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Step response Only Prop. - Gain=0.2N/  m (40  m gap) Settling time 1.5ms Command Position

15 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Step response FF Force Ctrl+FF Force

16 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Step response

17 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Step response

18 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Less Bandwidth wrt P36 G=0.8M/  m S.T.=0.7ms G=0.2M/  m S.T.=1.5ms 7.5mm P36MMT336 2mm Less damping, but better static control of the edge

19 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Turbulence compensation nm Input turbulence Residual of first 200 mode Correction (scale X10) r 0 =550nm, v=6m/s, 8sec 2.3  m rms 140nm rms on acts. Max 0.4N rms (|  T|<1.2 C) (Cap. sensor readings)

20 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Modal analysis (Cap. sensor readings)

21 Osservatorio di Arcetri Beyond Conventional Adaptive Optics, Venezia 7-10 May 2001 Conclusions The control gain achieved is high enough to ensure proper tracking and correction of atmospheric turbulence. The unit is now on the optical-test tower at the Mirror Lab for optical characterization Work is now in progress to optically flatten the mirror and calibrate the capacitive sensors According to the current schedule we plan to close the optical loop at the optical-test tower in June


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