1 1.Definition 2.Deliverables 3.Status of preliminary design 4.Risks 5.Tasks to be done 6.Decisions to be taken 7.Required simulations 8.Planning ISC workshop: Steady State Locking

2 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

3 2. Deliverables Internal: Correction filters definition Feed-forward technique filter definition Specifications on feed-forward techniques at DC ( coupling with locking accuracy) To other subsystems: Specifications on core mirror motions – RMS VIR-068B-08 Specifications on mirror control noise Specifications on RF oscillator phase and amplitude noise Specifications on IMC locking accuracy Specifications on IMC length noise PSD Specifications on laser frequency noise (OSD input: loss asymmetry, finesse) Beams / photodiode ports definition Specifications on DC powers on various photodiodes Specifications on sampling frequency and delays Specifications 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 Document Preliminary Design Document Pre-commissioning on a simulation software

4 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

5 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

6 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!! Without radiation pressure effects Not documented in AdLigo? DC detuning at stake

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

8 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

9 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

10 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