LBT Progress Report, Feb 21-24 2005 Marco Xompero 1/14

P45 Test Resultsand beyond…

Marco XomperoDaniela Zanotti

Armando Riccardi

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Overview

• Flattening P45 thin shell with bias magnets.

• Position noise characterization with new electronics.

• Thin shell step response.• Chopping? Chopping!• Test tower optical bench.

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Flattening P45

Actuator locations

finite element analysis: LBT672 shelldeformation due to local torque39 nm PtV / N mm => max: 2.3nm PtV

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Position Noise (1)

Typical RMS value reduced ~1.3 [nm]

INCREASE WORK DISTANCE!

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Position noise (2)

• Work gap: 68m• What do we expect? Noise increase prop. d2…• Different gain on different rings

– Proportional: Inner/Mid 0.1N/m Outer 0.1N/m

– Derivative: Inner 45 Ns/mMid 43 Ns/mOuter 90 Ns/m

• Double derivative guard pole at 15kHz

2dn

Typical RMS ~3.5 [nm]

High derivative means air damping substitution

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Step Response (1)

New settling time: ~0.57[ms] to ~0.67[ms]

Old settling time: 0.7[ms]

Other Modes Cross Talk

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Step Response (2)

Mid stiffness mode High stiffness mode

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Chopping • 128 m gap• Proportional: In, Mid, Ext 0.04

N/m• Derivative: In, Mid 10 Ns/m,

Ext 20 Ns/m• Edge PtV tilt ~140m i.e.

~14 arcsec on the sky• Chopping frequency ~5Hz

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Chopping (2)

Settling Time ~10ms

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Chopping (2)

K Band d.l. size: ~53[mas]

Rms ~3.2 [mas]

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Optical test tower (1)GOALS:• Avoid air convection• Minimum hexapod movement to correct defocus term in the optical path

SOLUTION:Local thermal stability in all tower length within 0.1 ◦C(ex: INVAR support add only 30 nm defocus term)

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N S

Optical test tower (2)

H20 + Glycole

Out

In

TemperatureSensors(PT1000)

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Summary

• Bias magnets increase the safety and induce acceptable mirror figuring errors.

• P45 new control devices and sensors are ok!

• We can work easily from 68m to 130 m.• New electronics improved settling time.• Chopping require optimization but we are

not so far!• The temperature control of optical test

tower has been tested to be in spec.

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The End?

The End!