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LESSONS FROM VIRGO+

May 17th 2010

E. Calloni for the Virgo collaboration

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Difficulties and hopes

• Control of many degrees of freedom• Aberrations• Environmental noises • Definitions of mid term scientific goals

• Stability of the mirrors • Use of NDRCs for high power ITF • Long work expected on environmental noises • Involve theoreticians in time scheduling?

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Some remarks on VSR2

Science Mode duty cycle > 80%

Locked duty cycle > 85%

Interferometer working mode particion

Start July 07 2009End January 08 2010

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Sensitivity and Horizon

Hzh /1~

10-23

10-20

Sensitivity of Virgo+during VSR2 (red)compared with theoricalsensitivity (black)

Horizon for 1.4-1.4 NSNS solarmasses for a typical lock

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Sensitivity in good agreement with Noise Budget projections

Recent noise budget with input power P0=17Watts. The total noise (pink curve)

also includes the expected thermal (pendulum and mirror) noises

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Difficulties of control many degrees of feeedom

• Alignment – the present control of alignment degrees of freedom is already complex and at the limit of noise reintroduction

Residual (before closing the global alignement ) picth RMS about 0.8 rad

Having the quiet mirrors alsohelps in lock acquisition (0.1m/s) and in reducing control noises

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Complexity of ADV detectorsMore degrees of freedomNDRCs lower the higher order modes thus error signal amplitudes High circulating power radiation pressure effects

Important to start with qiuet mirrors

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10 10010-23

10-22

10-21

10-20

10-19

10-18

Sensitivity comparisonh

(f)

[1/s

qrt

(hz)

]

Frequency [Hz]

VirgoNominal Qh1=Qh2=8E5, Viscous (Qv3=300) Qh1=Qh2=8E5, Structural (Qv3=100 ) Qh1=Qh2=8E5, Structural (Qv3=300 ) Sensitivity Jul13,09-22:00 LT (GPS h931550413) Sensitivity Oct19,09-20:30 LT (GPS h940005013) NewSensVirgo

Remarks on thermal noise

During VSR2 the noise between 20 -100 Hz was in agreement with the expected Thermal noise + a small contributions of the other measured noises in the band

10-22

10 100

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Installation monolithic suspensions

Comment: the lowering of noise at low frequency appears to require long commissioning time both for control noises and environmental noises. The incoming operation of ITF with monolithic suspensions is expected to give important contribution for Adv detector

Presently Virgo has two monolithic suspensions (input mirrors) installed and it is on going the installation of the other couples of monolithic suspensions (end mirrors)

Nominal sensitivity of Virgo+ with monolithic suspensions (black) and VSR2 sensitivity (red).At very low frequency the nominal Virgo+MSsensitivity is comparable with Adv-Virgo

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Aberrations

From this picture it is seen how the NDRC maintain a much higher recycling of the sidebands with respect to MSRC configurations. This is also true for the carrier for high aberration

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The sidebands in VSR2

• We used about 1 of TCS per mirror to obtain the above shape of the sidebands and 15 recycling gain

• The amount of TCS was limited to 1 Watt due to noise reintroduction (before TCS power stabilization (early october) ) and to not available time for otpimization during the run

During VSR2with about 1 W of TCS per mirror

Figure: sideband (left and right) and carrier (center) amplitudes at the output port of the ITF. As expected the carrier is highly aberrated (it is on dark fringe). The sidebands

“should” be gaussian

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Before and after installation of the two input

monolithic suspensions

Comparison of sidebands and carrier shapes at the output port before (upper) and after (lower) the installation of the first couple of monolithic suspensions and new input mirrors

VSR2

Present

Lower SB Carrier Upper SB

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Control during VSR2In these conditions of sidebands the control loops were not affecting the sensitivity. The projected noise with higher finesse and some tuning of loops is already compatible with Virgo+MS Adv-Virgo

The lesson from aberrations is somewhat “difficult” the early Adv detectors will probably be injected with “low power” (around 25 Watt ) and use only power recycling. Anyway the locking of the ITF can be acquired and maintained in presence of not negligible aberrations encouraging for the Adv

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Environmental noise

• Up conversion of low frequency seismic noise• Seismic and acustic noise due to Air conditioning

machines, cooling fans…..

• Magnetic noise…..

Modal analysis of NEB optical bench: (Left) measured map of bench motion with respect to ground; (Right) simulation of bench first structural mode. stiffen the legsdamp the resonances……

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Environmental noises reduction• Reduction of diffused ligth noise (bench alignments, isolation of

pumps and funs), magnetic studies and reductions, dust protections• TCS Power stabilization

Time – frequency plotof dark fringe spectrumbefore and after turbopump replacement witha smaller one

Free running (blue) andcontrolled relative intensitynoise of CO2 laser

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Environmental and glitchness

Rates of glitches for different SNR (central frequency < 150 Hz) for the whole VSR2. Each point correspond to 6 hours of data

After the commissioning break of early October the high SNR glitches rate is greatly reduced, to less 10-4 Hz, mediated on 6 hours of data, in normally quiet (not high microseism) conditions.

Comment: the reduction of environmental noises can profit of a good collaboration between commissioners /data analysts (Data Quality) and should be encouraged in Adv detector

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Experimentalists and theorists

Horizon for 1.4-1.4 NSNS solarmasses for a typical lock

Horizon as a function of total binary mass system for Virgo in June (blue curve) and in October (green), compared with the two Ligo detectors in the same period

Comparison with Ligo detectors show that for high solar mass systems Virgo maintains a remarkable horizon, but it is very difficult to work in coincidence

for high masses of the system.

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The case of Virgo+ Monolithic suspensions

Virgo+ with monolithic suspensions will leave a short life: it will be closed in July 2011 to start Adv-construction.

Probably it will not have time to reach his potential sensitivity. A tight collaboration among experimentalists and theorists could define better where to strengthen the commissioning efforts.

In the same way in case of Adv-Virgo a tight collaboration between theorists and experimentalists could be important in the various stages of the evolution of the sensitivity

Medium term expected sensitivity for Virgo+MS

Anticipating in very low frequency the sensitivity of Adv what could be searched for?Can we help in shortening the “desert crossing” of data?