Commissioning status of the Virgo interferometer

Bas Swinkels European Gravitational Observatory

on behalf of the Virgo collaboration B. Swinkels – Virgo commissioning status –8, Amaldi Amaldi June82009,

1 Columbia University

Commissioning timeline ●

May '07 - Sep '07

First Virgo Science Run (VSR1)

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Oct '07 - May '08

Commissioning

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Scattered light mitigation: replaced brewster window by cryotrap

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TCS installation, mirror magnets strength reduction

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9 May '08

Vacuum viewport failure

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May - Oct '08

Virgo+ shutdown

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Injection system, infrastructure and electronics upgrade

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NE payload recovery, replacement of all viewports

Oct '08 - now

Commissioning

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Remaining electronics upgrade

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Commissioning with more input power and TCS

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Baffle problems

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7 Jul '09

Start Second Virgo Science Run (VSR2)

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2010

Monolithic suspension upgrade? B. Swinkels – Virgo commissioning status – Amaldi 8

This talk

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Incident recovery

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Caused by weak design of view-port, identified and tested safer model

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Replaced about 90 view-ports throughout whole interferometer

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Cleaned and tested North-End tower

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New payload at North-End: coating of already polished spare mirror B. Swinkels – Virgo commissioning status – Amaldi 8

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Interferometer restart

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Interferometer no longer showed bi-stability during lock acquisition

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Different working point: modulation frequency changed by 700 Hz

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Maybe caused by slightly different radius of curvature of new mirror B. Swinkels – Virgo commissioning status – Amaldi 8

4

Virgo+ upgrade: injection system ●

New laser amplifier: up to 60 W (25 W at interferometer input)

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New pre-mode-cleaner

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Remotely tunable in-vacuum Faraday Isolator

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Heavier input-mode-cleaner end-mirror

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See poster by E. Genin

B. Swinkels – Virgo commissioning status – Amaldi 8

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Virgo+ upgrade: electronics

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Replaced real-time fiber links: more flexible signal routing

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Replaced old RIOs by real-time PC: much more computing power

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New ADCs: from 16 to 18 bit

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New quadrants read-out electronics for alignment B. Swinkels – Virgo commissioning status – Amaldi 8

6

Virgo+ upgrade: infrastructure ●

Replaced complete wiring of main power and grounding in central building

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Replaced and doubled UPS

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Replaced 15 kV transformer

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New hot water pipes

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Lowered speed of airconditioning

B. Swinkels – Virgo commissioning status – Amaldi 8

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Thermal Compensation System

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Annulus and central spot from CO2 laser on both input mirrors Essential for compensating thermal lensing in input mirrors when working with high input powers

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Not yet stabilized in amplitude, some evidence for introduced noise

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See poster by A. Rocchi B. Swinkels – Virgo commissioning status – Amaldi 8

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Phase camera field amplitude

phase between fields

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Beam scanned on pinhole detector, signal demodulated to separate carrier and sidebands

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Located on dark fringe before output-mode-cleaner (B1p)

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Extensively used, but more as 'amplitude camera'

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TCS fine alignment, 'cold interferometer' experiments

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Mirror cool-down experiments to measure coating absorption

See presentation by R. Day on Thursday B. Swinkels – Virgo commissioning status – Amaldi 8

9

High power operation ●

Power increased in steps from 8 W (VSR1) to 17 W now –

limited by mismatching of reference cavity due to thermal effects

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No major problems with interferometer stability

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Some alignments loops more critical

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Quadrature signals (B1_ACq or B5_ACq) kept close to zero using slow servos on TCS power

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Currently about 1.5 W on both mirrors: interferometer similar to 8W

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'Cold interferometer' with about 2x 6W –

More optical gain, ideal frequency stabilization TF, but TCS too noisy

without TCS B. Swinkels – Virgo commissioning status – Amaldi 8

with TCS 10

Scattering from baffles (1)

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Sensitivity was spoiled up to 400 Hz after vacuum intervention

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Caused by scattering from suspended baffle, already installed year ago

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Probably moved by a few mm during vacuum intervention B. Swinkels – Virgo commissioning status – Amaldi 8

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Scattering from baffles (2)

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Several failed vacuum interventions to fix problem

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Root cause: reflection of uncoated output window

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Problem finally solved by absorbing glass on suspended bench B. Swinkels – Virgo commissioning status – Amaldi 8

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Noise budget ●

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Low frequency –

Some environmental

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Some scattering

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Laser bench resonances

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Actuator noise

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No control noise!

Medium frequency –

Coating thermal noise

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Detection bench resonances

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TCS radiation pressure?

High frequency –

B. Swinkels – Virgo commissioning status – Amaldi 8

Shot noise

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Sensitivity

May 2007: ~3 Mpc May 2009: ~8 Mpc

B. Swinkels – Virgo commissioning status – Amaldi 8

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Future work ●

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Before the run –

Damp external bench resonance (sorbothane)

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TCS power stabilization?

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Bellow between turbo pump and tower

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New phase-camera on B5 beam (beam-splitter pick-off)?

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Noise hunting

During the run (commissioning breaks) –

Replace detection output window, with AR coating?

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More noise hunting

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Stabilization of 'etalon effect'

Long term –

Monolithically suspended mirrors, finesse 50 -> 150

B. Swinkels – Virgo commissioning status – Amaldi 8

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Concluding ●

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Robust interferometer –

81 hour lock during Easter

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WSR13/E14: 95% duty cycle

Stable horizon: 8-8.5 Mpc –

fluctuating with input mirror etalon effect

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Low glitch rate: factor 10 lower than VSR1

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Almost ready to start VSR2

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Preparing for installation of monolithic suspensions

B. Swinkels – Virgo commissioning status – Amaldi 8

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End

B. Swinkels – Virgo commissioning status – Amaldi 8

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