Alignment status & plans

2nd modulation frequency absolute (demodulated) reference for common end alignment (not available with one fmod) Previously aligned with ITF reflection Q21_DC 2nd mod. (8.35 MHz) IMC mod. (22.4 MHz) Virgo mod. (6.26 MHz) 2nd mod. on the same EOM => line forest => difficult Solution: 2nd EOM => Much less problems but modulation must be weak (m=0.01 instead of 0.17) for avoiding perturbations => to be investigated

2nd fmod layout WSR10 alignment layout 6.26 MHz 8.35 MHz

2nd fmod: results 8 MHz modulation is working Common end loop adapted Low modulation index => Q22 signal noisy => use at LF Common end loop adapted Error signal remains Q21_DC Absolute Q21 position set by shifting until Q22_AC = 0 (Alp loop; stopped in science mode) Alternative possibility “Mix” Q22_AC (LF) <=> Q21_DC (HF) One error signal; filters in sensing matrix Advantage: absolute DC reference is kept during science mode Q21_DC Q22_8 MHz

End mirror beam centering - before DSP Drift control QD error signal B8_q1_DC B8_q2_DC B7_q1_DC B7_q2_DC B8_q1 B8_q2 B8 WE B7_q1 WI PR NI NE B7_q2 BS B7

End mirror beam centering - now Alp Drift control Alp error signal 7...8 Hz line on NE/WE tx/ty Locking correction in z => control input mirrors Noise reduction but: upconversion 10-15 Hz ?! B8_q1 B8_q2 B8 10 Hz before after (high ISYS noise!) WE B7_q1 WI PR NI NE B7_q2 BS B7

Alignment noise in dark fringe G. Vajente Automated alignment noise projections (10 min.) Coherence Differential end mirror tx mode almost limiting => more power on Q1p diode + whitening filter => alternative: improve corrector cut-off (but: need all margin for high LF gain)

Recent Gc-Ali upgrades Sensing – Filtering – Driving available Driving switch needed during thermal transient (switch NE-WE => Common-Differential) Noise injection For measurement of open loop transfer functions Filtering gain change on-fly For migrating all gain changes from DSP to Gc Noise Sensing Filtering Driving DSP Global control

Alignment OL transfer function measurements Differential end tx Excellent fit with Matlab model Gain adjustment => matrix calibration Differential end ty ? Less excellent fit But still good in the important region (a few Hz)

Diff end tx error signal Other improvements Thermal transient robustness Improved by switching on 1. differential 2. common end alignment Driving matrix NE/WE => NE+WE/NE-WE after thermal transient PR alignment acts on reference mass Local control on marionette remains on High gain filters (end mirror control) Further tuning needed Sometimes more gain than needed => Rather invest in HF cut-off Histogram Diff end tx error signal

Plans up to scientific run I Improve alignment stability (filter work) Sometimes oscillations during thermal transient Check stability in bad weather conditions Reduce alignment noise 10-50 Hz: alignment noise starts becoming important Error signal improvement (B1p: more light + preshaping) Filter tuning (LF gain / HF cutoff trade-off) Continue transfer function measurements Line injections for better coherence Understand model deviations Measure resonance frequencies: rad. pressure effects? Update sensing matrix Continue alignment globalization More logical system: all gain adjustments in Gc, …

Plans up to scientific run II Common mode error signal improvement Create composite error signal (mix Q22_ACLF + Q21_DCHF) Observe beam centering loops Improve if needed (up-conversion, better centering, …) Centering of input mirrors? TBC

To be done if needed Switch BS/ISYS <-> NI/WI control LA on NI/WI mirrors BS/ISYS steer beams in arms Globalize other LA degrees of freedom PR, BS PR alignment Keep LC on marionette on? Optimize IMC alignment filters Reduce LF beam jitter (higher gain) Increase 8 MHz modulation index First understand where locking signal perturbation comes from

End

Alignment configurations tx IB PR BS NI NE WI WE ty IB PR BS NI NE WI WE 10 d.o.f. fast alignment WSR1 08/09 – 11/09/2006 tx BM PR BS NI NE WI WE ty BM PR BS NI NE WI WE 6 d.o.f. fast alignment; input beam and BS control WSR10 09/03 – 12/03/2007 7 d.o.f. fast alignment; input beam and BS control XX Linear alignment XX LA (ref. mass) XX Drift control XX Local control XX DC error signal XX DC + AC err.sig.

WSR10 sensing matrix BMS PR BS NI NE WI WE ThetaX 0.5 B1p_q1_ACq 4 B2_q1_ACp 2 B5_q1_ACq -0.5 B8_q1_ACp -1.5 B2_q1_DC 1 B7_q1_DC -1.5 B7_q2_DC 1 B8_q1_DC -0.8 B8_q2_DC BMS PR BS NI NE WI WE ThetaY -0.6 B1p_q1_ACq 4 B2_q1_ACq 0.4 B8_q1_ACq 4 B2_q1_DC -1 B7_q2_DC -0.7 B8_q2_DC * Filtered in Gc sensing

WSR10 alignment control overview Beam Diode Demod. Loop Arm diff. B1p Q Fast Arm common B2 1 2 for centering - PR B5 BS B8 P (tx) Q (ty) Fast (tx) Drift (ty) NI B7 1+2 Drift WI BMS

WSR10 alignment filtering Sensing Filtering Driving DSP Global control Sensing Filtering 1 DC Filtering 2 Initial Filtering 3 Boost DSP PR tx --- Ref.mass + mario LC PR ty End tx INITIAL BOOST End ty

WSR10 alignment driving Sensing Filtering Driving DSP Common End Global control Driving 1 Initial_Driving Driving 2 Driving Common End => NE => NE+WE Differ. => WE => NE-WE