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Considerations in Choosing an ISC Sensing & Control Configuration

Considerations in Choosing an ISC Sensing & Control Configuration. Rana Adhikari. 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)

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Considerations in Choosing an ISC Sensing & Control Configuration

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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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