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1. Definition2. Deliverables3. Status of preliminary design4. Risks5. Tasks to be done6. Decisions to be taken7. Required simulations8. Planning

ISC workshop:

Steady State Locking

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SSL

- defines modulation frequencies- ensures robustness and reliability- ensures that control noises do not contribute to the dark fringe “sensitivity” (h/sqrt(Hz))

1. Definition

Steady state control of all longitudinal degrees of freedom

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2

2

yxs

yx

yxp

YX

YX

lllSREC

llMICH

lllPRCL

LLCARM

LLDARM

cm3

m10

MICH

11

DARM

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2. DeliverablesInternal:

Correction filters definitionFeed-forward technique filter definitionSpecifications on feed-forward techniques at DC ( coupling with locking accuracy)

To other subsystems:Specifications on core mirror motions – RMS VIR-068B-08Specifications on mirror control noise Specifications on RF oscillator phase and amplitude noiseSpecifications on IMC locking accuracySpecifications on IMC length noise PSDSpecifications on laser frequency noise (OSD input: loss asymmetry, finesse)Beams / photodiode ports definitionSpecifications on DC powers on various photodiodesSpecifications on sampling frequency and delaysSpecifications on beam quality?Definition of detuning (OSD input: contrast defect) Actual modulation frequency definition. (OSD input: lengths for PRCL and SRCL)

System project management:Design Requirement DocumentPreliminary Design DocumentPre-commissioning on a simulation software

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3. Status (1/2)

Design requirements identified

• Radiation pressure – effects in Open Loop TF

• Optickle identified as adequate software

– Stability issue of arm cavity with DC locking• Digital spring to compensate optical spring?

• Sensing diagonalisation– Multi-modulation scheme

• But dark fringe DC locking at risk, see later

• Signal recycling• Auxiliary DoF’s noises introduced in dark fringe

– Shot noise correlations

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3. Status (2/2)

Conceptual design

• Several notes by Gabriele

• Frequency stabilization: architecture identical to initial Virgo– Relaxes requirements on feedback loop shape at 10 Hz.

• Pending: double vs. single demodulation

Preliminary design

• Specifications on core mirror motions

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4. Risks

DC detuning and dark fringe locking

• “Hierarchical gain” technique used when auxiliary DoF is not negligible (reduces contribution in error signal PSD)

• But here auxiliary DoF dominates at DC by a factor 10!!

Not documented in AdLigo?

DC detuning at stake

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5. Tasks to be done

Design tasks– Shot noise correlations and feed-forward corrections to be checked – DC locking of dark fringe: hierarchical gain, MIMO?– Frequency stabilization architecture– Digital SSFS?– Optical spring recycling cavity: opto-mechanical frequency changes– Need for 2f, 3f signals?– MSRC: feasibility of the evaluation of the noise due to the high order

modes?

Design specification tasksPre-commissioning tasks

– Simulation with all loops (time, frequency domain?)with procedures similar to AdV to define demodulation phases, etc.

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6. Decisions to be taken

• Small Schnupp asymmetry (~4cm) taken as granted – VIR-049A-08, G. Vajente

• Single vs. Double demodulation scheme– “Double demodulation” re-introduces less noise from extra DoF’s

– Offsets from sidebands on sidebands?

– “Double demodulation” requires one SB with amplitude modulation

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7. Required simulation

• Transfer functions for laser amplitude/frequency noise

• MSRC: noise from extra modes? (not a priority)

• Learn on parameter tuning required accuracy (feed-forward techniques, demodulation angles, etc.)

• Global system stability

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8. Planning

• Manpower needed!

• More interaction with AdLigo?

a. DC locking case

b. Single vs. Double demodulation

c. Modulation frequency definition

d. Specs for INJ/LAS

e. Specs for PAY/SUS