virgo – i njection sys tem …today and tomorrow… olivier fran Ç ois

Olivier FRANÇOISVirgo Injection SYStemPasadena, 01/18/2005

Virgo – Injection SYStem

…Today and Tomorrow…

Olivier FRANÇOIS(European Gravitational Observatory)


Introduction

ISYS nowadays… Current problems/limitations Next upgrades


ISYS today…situation wrt the interferometer


ISYS today…the Injection Bench

S

N

O

EM1

M6

M3

Dps

M2

M4

M5

Mode Cleaner transmission

Mode Cleaner reflection

RC (reference cavity)

Toward Mode Cleaner

Toward the interferometer

From the Laser Lab

Beam going through M1 and

entering the RC


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 alignedPR aligned

PR misalignedPR misaligned

IMC control loop for freq stab is perturbatedIMC control loop for freq stab is perturbated


PR backscattering & IMC instability

Temporary solution:Temporary solution: decrease to 10% the amount of light transmitted to the ITFdecrease to 10% the amount of light transmitted to the ITF(1% of the light is back-reflected by the PR into the MC)(1% of the light is back-reflected by the PR into the MC)

Definitive solution:Definitive solution: Implement a Faraday isolatorImplement a Faraday isolatorNot enough room on the current IB>redesignNot enough room on the current IB>redesign


IB resonances

diam. Inox wires:= 2mm + couplersweight # 113 Kg

T:RotationU: transaltion

Mode Frequency

Ty/Ty Tx/Tx Tz/Tz Ty/-TyUy/Uy ==> [0 : 1.2 Hz]pendulum I & IIUy/-Uy 34.2 HzTx/-Tx 39.2 HzTz/-Tz 42.4 Hzmarageing violin 112 Hzdihedron [110,142,144 Hz]Susp. wires(+couplers) violin 50 Hzreference cavity I 208 Hz

RECTANGULAR BENCH

IB internal modesIB internal modes Susp. wiresSusp. wires

Finite element model analyisFinite element model analyis


IB resonances

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


IB resonances

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

26/06 C4: control from the ground coils

07/09 DT: control from the marionetta

Before frequency tuningAfter frequency tuning


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=> The MC mirror will be changed


Present Injection System alignment scheme

Ref. cav.

MC lock frequ. prestab.

MC

LC

LC

RFC auto- alignment

-- lock servo MC auto- alignment-- alignment servo

lock MC length on RFC

picomotorspiezos

Laser

Matrix

NFFF NF

ty tx

FF

h

vh

v

ABP

h

M2

M3M5

M6

Matrix


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: new alignment scheme

Ref. cav.

MC

LC

IMC auto- alignment

-- alignment servopicomotorspiezos

Laser

NFFF

NF

FF

ABP

M2

M3M5

M6

Matrix

Matrix

ABP

RFC auto- alignment

Beam pre- Alignment

(Frederic Cleva)

Beam driftcontrol

New automatic alignment system New hardware is needed

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 neededIt allows thermal regulation of the PR cavity reflectivityAn off-axis parabolic mirrors for the telescope in the IB has to be assembled

IMC: waist 4.9 mmCondensing 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

virgo – i njection sys tem …today and tomorrow… olivier fran Ç ois

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