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Optimizing ISC Sensing & Control Configurations: Guidelines & Considerations

This guide provides recommendations for selecting ISC sensing and control configurations, covering compatibility, RF modulation, detector requirements, noise budgets, and control strategies. It includes considerations for LSC and ASC schemes, exploring various sensing schemes, noise budgets, and control parameters for each setup to ensure optimal performance.

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Optimizing ISC Sensing & Control Configurations: Guidelines & Considerations

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  1. Considerationsin Choosing anISC Sensing & Control Configuration Rana Adhikari

  2. A Starting List • Compatibility • LSC/ASC schemes are coupled. Should be developed synchronously • Baseline: RF PDH length sensing, WFS+Oplevs for ASC • LSC • DC Readout at the AS port (w/ OMC f_pole ~ 1 MHz) • Frontal RF Modulation • Baseline uses ~200 MHz RF. Let’s change to (f1+f2) < 100 MHz as a soft requirement to ease electronics (detectors, demods, oscillators) • Assume 100 mW detected per PD (REFL (all), PO (1000 ppm), AS/100) • Finite dynamic range RFPDs: 100 mVpk, 1 nV/rHz • ASC • Same readout ports as in iLIGO. Exploring DD, 3f, NRSB, etc. • Optical Torsion Spring @ 6 Hz with 1 MW in arms. WFS bandwidth becomes ~15 Hz. iLIGO has ~5 Hz BW and 40 Hz GW frequency. • Need very, very low noise WFS system. No more crappy iLIGO WFS.

  3. LSC Considerations • Evaluate Sensing Schemes • Use Finesse (or equivalent), develop SNR matrix using previous pages constraints on f_mod and PD range and detected power. • Make a LSC ‘Noise Budget’ of couplings (L+, l+, l-, ls). • First evaluate for baseline of 125 W; NS/NS tune. Later do 10 W, BH Tune • The Matrix • Let’s try to ignore having a ‘diagonal’ matrix; (we have digital controls) • G budget: Less than 1% of carrier power robbed for each SB • Explore all intermodulations: DiffDemod, DoubleDemod, 3f, SSB, NRSB, 1f, 2f, etc. • Controls • Conservative assumption of factor of 30 subtraction via off-diag correction paths. iLIGO gets ~100x for MICH & ~10x for PRC. • 50 Hz UGF for all the short DOFs, 1/f loops. CM Servo has 10 kHz BW. • Pay no attention to Lock Acquisition. Will be developed by 40m team.

  4. ASC Considerations • Evaluate Sensing Schemes • Use Finesse (or equivalent), develop SNR matrix using previous pages constraints on f_mod and PD range and detected power. • Make a ASC ‘Noise Budget’ of couplings. • First evaluate for baseline of 125 W; NS/NS tune. Later do 10 W, BH Tune • Will probably need to develop WFS w/ 10^-16 rad/rHz sensitivities. • The Matrix • Let’s try to ignore having a ‘diagonal’ matrix; (we have digital controls) • G budget: Less than 1% of carrier power robbed for each SB • Explore all intermodulations: DiffDemod, DoubleDemod, 3f, SSB, NRSB, 1f, 2f, etc. • Explore stable v. unstable recycling cavities (long & short). • Controls • Conservative assumption of angle->length coupling of 1 meter/radian. • 15 Hz UGF to handle the optical stiffness. Might be relaxed for some DOF.

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