1

1. ISC scope and activities

2. Initial Virgo status

3. Design requirements

4. Reference solution and design status

5. Plans toward completion

6. Technical risks

Outline

AdV

ISC subsystem

François BONDU for ISC group

2

ISC scope and activities

Bring the interferometer to its operating point and keep it here reliably

• Lock acquisitionF. Cavalier (LAL-Orsay), G. Vajente (INFN Pisa – Pisa U)

• Steady state length controlG. Vajente (INFN Pisa – Pisa U)

• Angular controlM. Mantovani (EGO)

• Parametric instabilitiesP.-F. Cohadon (LKB - Paris)

Scope details, task list, interactions with other systems: VIR-085A-08

3

ISC scope and activities

2

2

2

yxs

yx

yxp

YX

YX

lllSREC

llMICH

lllPRCL

LLCARM

LLDARM

Longitudinal control

cm3

m10

MICH

11

DARM

4

Initial Virgo control

5

8MHz

MICH

6MHz

PRCL6MHz

DARM

6MHz

CARM

FREQ

Initial Virgo length control

6

Initial Virgo length control

Feed-forward techniques: VIR-050A-08

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Initial Virgo angular control

reconstructionmatrix

8

Initial Virgo angular control

reconstructionmatrix

9

Lock acquisition:

• Reliability of lock acquisitiontransients, bandwidthhigh speed mirrors when bad weather

• Actuation compatible witha low-noise “science mode” operationreduced sensitivity to magnetic noises

• Deterministic lock acquisition

Design requirements (1/4)

Ex. vmir = 1 m/s

Initial virgo:Tres / Tsto = 10-2 / 2 10-4 >> 1

AdV:Tres / Tsto = 5 10-4 / 3 10-2 << 1

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Steady state length control:

• No noise from auxiliary degrees of freedom

• Design with radiation pressure effects

• Additional signal recycling cavity

• Multiple inputs multiple outputs systemobservabilityrobustness

Design requirements (2/4)

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Alignment:

• Alignment lock acquisition compatible with local controls performances

• No noise in gravitational wave channel from alignment signals

• Design with radiation pressure effects

• Multiple inputs multiple outputs system (18 d.o.f.s)

observability; robustness

Design requirements (3/4)

LIGO P030055

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Parametric instabilities:

• Should not affect interferometer performances

• Evaluation of PIs in AdV configuration

• Passive or active mitigations

Design requirements (4/4)

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Reference solution (1/4)

Lock acquisition

• Arm cavity lock acquisition first, with auxiliary lasersCALVA experiment at LAL

• Sensing: laser with 3 modulations

• Driving: Variable finesse

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Reference solution (1/4) Lock acquisition

CALVA experimentEGO-PRE-STAC-102

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Reference solution (2/4)

Steady state length control

• Simulation of transfer function with radiation pressure: Optickle (LIGO)

• Increased complexity (almost) diagonal sensing matrixlaser with 3 modulations

• Driving: low noise operationFeed-forward techniquesSuspension hierarchical control

• Robust operation of a multiple inputs multiple outputs system

With

out

radi

atio

n pr

essu

re e

ffec

ts With radiation pressure effects

VIR-068B-08

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Reference solution (2/4) Steady state length control

CarrierSB1 9.4 MHzSB2 65.6 MHzSB3 8.3 MHz

VIR-068B-08

D.O.F. Single demod. Double demod.

DARM AP_DC AP_DC

CARM SP_SB1_P SP_SB1_P

PRCL SP_SB3_P SP_3+1_P

MICH SP_SB2_P SP_2-1_Q

SREC SP_SB1_P SP_2-1_Q

cm3MICH

displacement of towers

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Reference solution (2/4) Steady state length control

Schnupp asymmetry and Tower displacements:

• Virgo Schnupp asymmetry (80 cm)+ low SB2 transmission to SREC (diagonalization)

Modulation frequency for SB1 ~ 170 MHz

NOT compatible with high-power, high efficiency photodiode response (DET)

• Small Schnupp asymmetry

This reference solution

Tower displacement and infrastructure modifications

VIR-049A-08

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Double demodulationSingle demodulation

Use of initial Virgo feed-forwad techniques VIR-050A-08

Reference solution (2/4) Steady state length control

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Reference solution (2/4) Steady state length control

R.M.S.

(m)

S.D. @ 10 Hz

(m/√Hz)

DARM 2.0 10-14 7 10-20

CARM 1.3 10-14 1 10-16

MICH 1.1 10-11 4 10-17

PRCL 9 10-11 7 10-16

SREC 1 10-10 6 10-18

VIR-080A-08

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Reference solution (3/4)

Alignment

• Sensing: same modulation frequencies as for the length controlWard technique for arm cavity alignmentcompleteness of sensing matrix (NDRC)pick-off beams reflected by arm cavities

• Robust operation of a multiple inputs multiple outputs system

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Reference solution (4/4)

Parametric instabilities

Study:

• Parameters with AdV case

• Table-top experiment at LKB, active control?

• LIGO developments (passive / active control)

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Plans towards completion (1/2)

Documents

• ISC Design Requirement Documentmissing: lock acquisition: comparison of auxiliary laser / mirror decelerators

• ISC Preliminary Design Documentactuation (force) excursion range / noise sensitivitystability & robustness of MIMOS for lengths and alignmentspecifications for pre-stabilized laser linewidth

and arm cavity asymmetryalignment design: parameter tuning, negative torque mitigation

Planning

TBD

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Plans towards completion (2/2)

Decisions

• Alignment: give up Anderson-Giordano technique

• Steady state length control: single vs. double demodulation schemes

• Steady state length control: modulation frequencies and macroscopic lengths

• Lock acquisition: Combination of auxiliary laser / variable finesse technique

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Risks

• Alignment:Manpower:

18 dofs, tuning of telescope Gouy phases and demodulation phases, noisesnegative torque mitigation

• Parametric instabilities:Mitigation TBD

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ISC scope and activities

PAY/DETDAQ

VAC/IME

INJ/LASPAY

OSD

PAYDAQ

DAQ

• Lock acquisitionArm locking with auxiliary laserProcedure for full interferometer locking with “variable finesse” (from dark to bright fringe)

• Steady state length controlLinear locking design: modulation frequencies, macroscopic lengths, couplings, photodiode signalsFeed-forward techniquesLaser frequency stabilizationSpecifications on core mirror seismic isolation

• Angular controlWard technique (New for arm cavities)Parameter tuning for 18 degrees of freedomNoise specificationsModes with effective negative torque

• Parametric instabilitiesCase for AdV mirrorsActive control?