INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Adaptive secondary and primary mirrors for ELTs A. Riccardi 1, G. Brusa 1,2, P. Salinari 1, D. Gallieni 3 and R. Biasi 4 1 INAF-Osservatorio Astrofisico di Arcetri, Italy 2 CAAO, Steward Observatory, AZ, USA 3 ADS International Srl, Italy 4 Microgate Srl, Italy

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Corrector specs for ELTs actuators for the ground layer: D=50m about 100,000 D=100m about 400,000 Most challenging target: Multi-conjugate adaptive correction in V band seeing: 0.65arcsec (r 0 =0.16cm at 0.55mm) r 01 =22cm (60%) r 02 =28cm (40%) SC Fitting error=0.3 (d/r 0 ) 5/3 rad 2 MC Fitting error=0.3 [(d 1 /r 01 ) 5/3 + (d 2 /r 02 ) 5/3 ] rad 2 MC Fitting error == SC Fitting error with d= r 0 (d 1 /r 01 ) 5/3 = (d 2 /r 02 ) 5/3 = 1/2 d k = r 0k / 2 3/5 = 0.66 r 0k d 1 = 14cm, d 2 =18cm

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Corrector specs for ELTs So many actuators need: Low cost per actuator Reliable device Easy maintenance

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Currently avail. correctors Piezo technology Largest unit: Xinetics, 349 act., 7mm spacing (M=20). Position actuators (failure is a major problem), limited stroke for low spatial order correction (wind effects) MEMS technology Large number of acts., reduced stroke, 0.3mm spacing (M=466) Field=6arcmin, M=466: Relay optics F#=F/1.2 Adaptive secondary technology MMT unit: 336 act, 30mm spacing (first light end of June 2002) LBT units: 672 act, 30mm spacing (first light mid-2004) Force (electromagnetic) actuators, Large stroke (Chopping) See Brusa et al. Backaskog Workshop for a general theory N act > 300

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting People (some of them) Osservatorio di Arcetri INAF-OAA (Italy): Concept development. Testing, calibration and diagnostic software ADS (Italy): mechanical engineering, drawing and assembly Microgate (Italy): electronics and DSP software Media Lario (Italy): mechanical drawing and assembly CAAO-SO (USA): MMT AO Mirror Lab-SO (USA): optics and optical test facility

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting 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) support frame & interface to Hexapod electronics cooled crates 1Gbit/s communication link (optical fiber) hub interfaces (power, signal & cooling) System Layout

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting MMT336 ASPHERIC SHELL Assembled unit Magnets 642mm diam. 2mm thick (12mm diam) Cap. sensor armatures (ref.plate)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting 3 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

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Step response Only Prop. - Gain=0.2N/  m (40  m gap) Settling time 1.5ms Command Position

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Step response FF Force Ctrl+FF Force

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Step response

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Step response

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting 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)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Modal analysis (Cap. sensor readings)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Optical tests at Mirror Lab Shimulator (Steward Obs-Mirror Lab) Turbulence simulator (Steward) Test of the entire AO system: Adaptive secondary+ WF sensor+WF computer closing the optical loop

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting MMT336 Flattening The flattening of the shell applying 150 mirror modes: 34nm RMS The central rings are artifacts due to the olographic technique used for testing convex mirrors

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Closed optical loop Open loop Closed 550Hz MMT336+SH 12x12+WF computer Data from G. Brusa (CAAO-Mirror Lab)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting LBT672 summary 672 actuators in 14 rings 31mm act-to-act ave. distance 642mm 911mm MMT336 LBT672

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting LBT672 electronics 3x2 crates 14 ctrl board per crate (84 tot) 8 320Mflop/s 32bit-FP DSP per board (ADSP-21160) 2 actuators per DSP (336 tot.) Total computational power: 107 Gflop/s WF reconstruction on-board LBT672 ((32x32x2)x672)x2 op in 0.5ms = 6Gflop/s (5% res.) (8.4  s to compute the FF matrix)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Actuator spacing limit 30mm (possibly 25mm) Capacitive sensors:3nm resolution, 100  m range (DR propto area) Actuator Efficiency: proportional to sqrt of magnet and coil volume Interaction among magnets

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Adaptive sec. location OWL Euro50 Ground layer: 4m M2 (31cm) 10km layer: 1.5m M2 (83cm) Ground layer: 2.35m M6 (106cm) 8km layer: 4.2m M5 (60cm) K band J-H band I-J band H-K band

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Actuator spacing limit Adaptive secondary technology is available and ready for NIR correctors on ELTs

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Primary adaptive mirror No more problem of actuator spacing (M=1) Economical advantages: Less expensive magnet technology Euro50 segments: 70mm thickness OWL segments: mm thickness Gravity load is supported in more points: Primary adaptive mirror: 10mm thickness 86%-90% less glass!! High spatial frequency control: larger polishing residual error can be accepted at low and mid-spatial frequencies No Zerodur, borosilicate can be used. Cheaper!!

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting 2m segment layout 10cm/act 397 act/segment Local glass stiffness: 15N/  m (LBT: 672 actuators)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Main components Glass: 77.5kg/seg Honeycomb: 100kg/seg 400 Actuators: 80kg/seg Total: 258kg/seg Euro50 (70mm thick.): 543kg/seg.52% larger mass!! OWL (80mm thick.): 621kg/seg. 58% larger mass!!

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Support and maintenance

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Backplate FEA Deformation of the honeycomb when pushing: 238N/  m (glass: 15N/  m) Gravity load: 15  m PtV

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Actuator details Axial and tangential load: astatic levers?

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Actuator prototype < 2ms settling time

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Control electronics Control electronics, one box per segment: smaller then LBT672 In a multi-resolution reconstruction approach control electronics can work as WF reconstructor

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Primary mirror prototype 1200mm diam. 7x340mm segments 19 acts/segment

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Conclusions Adaptive secondary mirror technology is a proven technology that is available and ready for AO correction for ELTs in the NIR Effective correction in V band using non-primary mirrors requires a step up in the number of actuators with the right actuator density that is not available right now Adaptive secondary concept and technology can be applied to primary mirrors to achieve effective correction in V band Warning: delaying a solution for an effective correction in the V band for ELTs could avoid a future upgrade in this direction. Let’s think about a compatible V solution now!

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Cost goals

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting 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

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Control loop Commands from WFC - + DM k-th Curr. Driver + coil Capsens DSP of k-th channel 40kHz local loop DSP + Feed-forward + +

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Electronic damping 100  m gap no electronic damping Electronic damping test on P36 G PlantSens DD + - c ff PV: 0.5ms settling time 50Ns/m

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Electronic damping Natural vs. electronic damping: Natural damping reduces stroke Electronic damping is limited by delay and capsens noise New capsens for LBT: From 40kHz to 500kHz Reduced aliasing error Analog derivative (reduced delay) Electronic damp. 4kHz->50kHz G PlantSens DD + - c ff + + +

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Pyramid for co-phasing 3 DoF per segment 64x64 or 16x16 signal sampling points Interaction matrix dimension 156x6400 or 156x400 Signals for segment Differential piston Center act. Side actuator S. Esposito

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Closed loop simulations rms < /20 Each realization converges to /20 rms after 7 iterations maximum. An input wavefront Piston values of each segment S. Esposito

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Modal stiffness Actuator stiffness 0.2N/  m Local ctrl dominates FF dominates

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Backplate FEA: dynamics 84Hz 168Hz 201Hz 282Hz

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting Oscillation of the ribs: 3.1kHz (out of the bandwidth)

INAF-Osservatorio di Arcetri 3-4 May Tuorla Observatory Opticon Meeting 50m example 2m diameter segments About 600 segments 2mm gap between segments 10mm thick glass: 77.5kg/segment 46.5tons total