Virgo – Injection SYStem …Today and Tomorrow… Olivier FRANÇOIS (European Gravitational Observatory)

Current problems/limitations Next upgrades Introduction ISYS nowadays… Current problems/limitations Next upgrades

ISYS today…situation wrt the interferometer

ISYS today…the Injection Bench Mode Cleaner reflection   Toward Mode Cleaner Mode Cleaner transmission M4 M6 O S M2 N From the Laser Lab E M1 Dps M3 M5 Toward the interferometer Beam going through M1 and entering the RC RC (reference cavity)

Current problems/limitations Power Recycling back scattering and IMC instability Injection Bench resonances Mode Cleaner mirror defects Injection System alignment Monolithic Power Recycling mirror

PR backscattering & IMC instability PR aligned PR misaligned IMC control loop for freq stab is perturbated

PR backscattering & IMC instability Temporary solution: decrease to 10% the amount of light transmitted to the ITF (1% of the light is back-reflected by the PR into the MC) Definitive solution: Implement a Faraday isolator Not enough room on the current IB>redesign

Finite element model analyis IB resonances IB internal modes Susp. wires Finite element model analyis

IB resonances Higher frequency modes (dihedron, reference cavity, …) are more difficult to be identify

IB resonances 26/06 C4: control from the ground coils Many attempt to explain how IB resonance noise enters in the interferometer Local control noise enters through coil drivers noise Coherence between coil driver output and B2_ACq confirms this hypothesis Controlling from the marionetta improves only partially the noise On the 18-10-2004 it has been understood that the modulation frequency of the MC was about 70 Hz away the MC length matching frequency 07/09 DT: control from the marionetta Before frequency tuning After frequency tuning

=> The MC mirror will be changed MC mirror defects The source of a large part of the light scattering we have in the ISYS is due to the MC mirror That scattering is only partially due to dust contamination => The MC mirror will be changed

Present Injection System alignment scheme -- lock servo MC auto- alignment -- alignment servo lock MC length on RFC LC picomotors piezos MC RFC auto- alignment ty tx Laser M6 LC Matrix Matrix ABP M3 M5 M2 MC lock frequ. prestab. FF NF NF h h v Ref. cav. h v FF

Injection system alignment The stability and reproducibility of the IMC alignment is not completely reliable Present Injection System is automatically aligned on the RC: RC transmission drifts less than the Mode Cleaner one It would be better align separately IMC and RC

Power recycling mirror PR is a composite mirror It shows internal modes at low frequency (about 100 and 400Hz) These frequencies are changing in time They are making the locking more complex and the final noise higher

Next upgrades: IB redesign

Next upgrades: IB redesign

Next upgrades: IB redesign

Next upgrades: new alignment scheme New automatic alignment system New hardware is needed Beam drift control -- alignment servo picomotors piezos MC Laser M6 LC ABP M3 M5 Matrix M2 ABP NF IMC auto- alignment Ref. cav. Matrix FF NF Beam pre- Alignment (Frederic Cleva) FF RFC auto- alignment Matrix

Next upgrades: new PR In the last VSC it has been decided to make the PR flat and without wedge, like the Input Mirrors: A substrate is ready. Only coating time needed It allows thermal regulation of the PR cavity reflectivity An off-axis parabolic mirrors for the telescope in the IB has to be assembled IMC: waist 4.9 mm Condensing telescope FI: waist 2.65 mm M5: f= 75 mm M6: f = 600 mm Ø  10 cm to PR: waist=20 mm d= 675 mm

Next upgrades: OAPM telescope Thermal lensing effect [100m-10m] can be compensated (curved FI exit surface) Not necessary to implement a FK51 compensator