ao status and perspectives

LBT External Review December 4 2002

AO status and perspectives P. Salinari

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AO status and perspectives



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List of current AO developments

• Adaptive secondary mirrors * [Arcetri]• First Light AO system (including software) * [Arcetri]• Test tower for secondaries and First Light AO * [Arcetri]• Photon counting CCD detectors [Arcetri+Bologna]• Site turbulence measurements (g. SCIDAR) [SO+MPIA]• Second Light Multiconjugate AO (Nirvana) * * [MPIA+Arcetri]• Sodium line reference stars (Parsec) [MPE+ESO]• Rayleigh reference stars [SO]

. . . Too many for 20 minutes! I am going to (just) touch only those with a red dot (*) S. Esposito (*) and Tom Herbst (* *) will describe those with blue dots



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LBT AO milestones and keywords

1992: Decision to (try to) go with adaptive secondaries (AS) . . . (lot of work on MMT AS, pyramid wfs, lasers, MCAO)2001: Decision to go with a 672 actuator secondary and (in first light):

• with natural star AO (but upgradeable with a Sodium laser)• with pyramid WFS (upgradeable with photon counting CCD)

2002: Decision to give “strategic” status as second light instrument to the “Nirvana” interferometer using on each arm a natural star MCAO system with the following features:

• Layer Oriented• Double FoV (~ 6 arcmin outer FoV, ~2 arcmin MCAO FoV)• Triple conjugate on each arm (secondary + 2 Xinetics DM with 349 actuator each)

2002: The MMT adaptive secondary seems to work at the telescope!



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AO plans

At the moment we have AO plans for two of the four (double)Gregorian foci of LBT:• The “front bent Gregorians” (used by Lucifer)• The “rear bent Gregorians” (used by Nirvana).

What can we do for the other focal stations? [if we find the money]• For the “central bent Gregorians” (used by LBTI), we can easily adapt the “first light AO” system, adding a “chopped” AO mode (double or multiple Pyramid) [ ~ 0.5 M$]

• For the “direct Gregorians” (used by MODS), we are considering adapting the “ground layer” wavefront sensor of Nirvana, to provide “wide field” partial correction of seeing (~1/2) [ ~ 2.5 M$]



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AO summary

The current developments may in principle satisfy the adaptiverequirements of all the planned instruments using natural stars only,providing:

In the Near (and Thermal) IR:• Sufficient sky coverage (10% at high Galactic Latitude in J band)• High Strehl ratio (with relatively faint reference stars)

At shorter wavelengths (R, I):• Sufficient sky coverage at moderate Strehl (~ 0.2, Nirvana)• Seeing reduction on “wide” field (~ 2 arcmin) on most of the sky for MODS

Completing LBT adaptivization (without LGS) would cost about 3 M$

The NIR sky coverage could be increased by using two LGS [add ~ 3M$]



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Adaptive secondary mirrors

If these gadgets don’t workLBT can only use “Prime Focus”,First requirement therefore is:

Reliability!!!!



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Obtaining reliability

• MMT336 (in this contest) is a “prototype” on which we had more than two years of testing in the lab and ~3 very important weeks on MMT (until now)• All changes wrt MMT336 are being tested on prototypes (P1, P36) and then all together on the final prototype P45 • LBT672 units will be tested in a special test tower with final hardware and software reproducing site conditions (the same holds for the full adaptive system)• All LBT672 functions can be monitored (and operated) remotely for test, diagnosis, and software correction or upgrade by experts• The tower testing hardware and software (Fisba interferometer, retroreflectors, etc.) will be available at the telescope for periodic tests, maintenance, re-calibration



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Correcting problems discovered with MMT336

1. Position jumps (cured with better contacts with backplate)2. Cable chaos (cured with distribution boards)3. Coolant leaks (cured with heat sink re-design)4. Gap contamination by dust, cured with:

• Construction in clean room (and “clean sealing”)• Soft gaskets on new actuators sealing the gap• Larger gap (new electronic damping)

5. Various (connectors, power supplies etc.) (cured by replacement with safer components)6. Lack of AS figure-test on telescope (cured by adding it)

The testing at system level will be complete in the tower and repeatable on the telescope in daytime when required



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LBT672 layout

Hexapod

Interface flange andstructural support

3 cooled electronicsboxes

Fixed hexapodCold-plate and

actuator supportAstatic levers

50mm thick Zerodurreference-plate



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New actuator and capacitive sensor

Already tested on P1.

faster to allowhigher electronic damping

easier accessibility

more reliable connections

added “skirt” to better seal the gap

90kHz@-3dB



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Electronic damping test

P36 prototype Test(24 kHz@-3db)

Gap=100m

Settling time: >8ms

Settling time: 0.5ms

Not only reduces risk of gapcontamination,

it improves performances!

No e-damping

With e-damping



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Curing “position jumps”: Au versus Cr

Gold is the therapy!

(but the first attempt Of deposition on the P45Backplate was not really successful)



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Distribution boards (curing “cable chaos”)

“in principio erat caos”

Now we have distribution boards



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On LBT672 performances . . .

There is also some progress in other fields, beyond reliability,that are worth mentioning:• The new, much faster, communication lines, the new 32 bit floating point DSPs allow to handle more data in less time• The incresed computing power allow wavefront reconstruction “on board” • The new faster analog electronics allows faster settling AND wider gap (therefore larger chopper throw, piston correction in interferometry etc.)• The new Gigabit Ethernet connection allows parallel (not real time) data processing and system monitoring



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Secondary mirrors comparison

r0=15cm@500nm MMT LBT

Diameter 641 mm 911 mm

N act 336 672

Fitting error 72 nm 64 nm

Act efficency 0.5 N/W1/2 0.5 N/W1/2

Power (act) 0.41 W/act 0.19 W/act

Power (crate) 4.7 W/act 3.8 W/act

Comm. link 160 Mbit/s 2.9 Gbit/s

Comm. diagnostic No dedicated 400 Mbit/s

DSP 40 Mmac/s (16 bit int) 160 Mmac/s (32 bit float)



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Where are we with LBT672?

• Mirror 1 manufacturing started in Summer 2002• Pre-production of magnets, analog electronics, actuators mechanics tested and accepted in summer 2002. Ready for mass production.• P45 to be delivered in December 2002 (with “old” digital cards to complete the test of the new actuators and of the distribution boards)• New pre-production digital cards (BCU and DSP) due in Feb. 2003• Full test of new hardware/software in spring 2003• Mass production of components in spring/summer 2003• Assembly in clean room and test in tower in autumn 2003• Full AO system test in tower in winter 2003-2004• Transportation to site in spring 2004

Still (marginally) in time for “first light” in June 2004(but AO is not officially a first light capability)



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Testing the adaptive secondary

15m optical bench to simulate the telescope

Arcetri Solar Tower

Reference optics

Tube supported byIsolators

Optical Bench (WFS unit)



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Thermal control

Goals:

0.2 K stability (in open air)

ΔT=25 K wrt ambient

Double cylinder with ~ 20mbar pressure in the gap (Acetone: liquid-vapor phases in equilibrium like in “heat pipes”)

4cm hd polyurethane outer skin (3kW@ΔT=30K)



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Scope of the test

Adaptive Secondary Tests:•Optical Flattening and calibration•Optical behavior at “mountain” ambient temperature•Dynamical Behavior at “mountain” atmospheric pressureWFS Optical Test:•Optical interaction with LBT672•Optical Closed loop operation

Main target:Test and characterization of the Optical Closed Loop for the Complete and Final

AO System before 1st light



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Concept

F2

F1

F/15.0

F/1.22

13713mm

1064.7mm911mm

The ellipsoidal secondaryis illuminated by theinterferometer from one of itsfoci, light is retro-reflectedat the other one.

a spherical mirror is sufficientfor simple “flattening”, necessary for “passive” use



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Some optical details

WFS needs exit pupil on the AdSec mirror!No simple reference sphere:Collimating optics+flat on the pupil image

Parabola+flat Single Aspheric lens+flat

Spheric obj+flat



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More details

Fisba interferometer

Movable beam-splitter

Beam to/from AdSec

Beam to WFS



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Where are we with the assembly and test facilities?

• The clean room is in operation (but used for LBC till summer 03)• Bids for Civil Work and “Heat Pipe” are out (offers due 12/20/02)• Orders of components done (Fisba interferometer, vibration insulators) or being done (winch, special o-rings . . .)

All the subsystems should be installed and go trough acceptance tests in June 2003

As the test tower is a fairly complex system in itself, we think of spending a few more months in tuning up the test tower

LBT672 should go in the test tower in October 2003



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A more detailed schedule



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The End

Any question?



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Photoncounting CCDs

The new E2V (ex-Marconi)back illuminated LLLCCD 60delivered to Arcetri on Nov. 21st

Its features:high internal gain (>1000)high QE (~ 90% in R)fast (16 Mpix/s, 1000frames/s)128x128 pix24x24 μm pix



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ao status and perspectives

Documents

light ao system

ao status

ao plansat

natural star ao

adaptive system

mmt adaptive secondary

chopped ao mode double

arcetri test tower