1. 1 ILIAS WG1 meeting, Hannover 23.01.2007 The 2 nd modulation frequency project

2. 2 ILIAS WG1 meeting, Hannover 23.01.2007 Motivation for 2 nd modulation

3. 3 ILIAS WG1 meeting, Hannover 23.01.2007 Quadrant diode locations Quadrant diodes give: “DC” signals: beam position on QD good for beam pointing control “AC” signals: demodulated signals good for cavity alignment

4. 4 ILIAS WG1 meeting, Hannover 23.01.2007 Beam splitter alignment Drift control (30 mHz) Autoalignment (3 Hz) AC

5. 5 ILIAS WG1 meeting, Hannover 23.01.2007 Power recycling mirror alignment Drift control (30 mHz) Autoalignment (3 Hz) AC

6. 6 ILIAS WG1 meeting, Hannover 23.01.2007 Input beam alignment Drift control (30 mHz) Autoalignment (3 Hz) AC

7. 7 ILIAS WG1 meeting, Hannover 23.01.2007 Input mirror alignment (beam pointing) Drift control (30 mHz) Autoalignment (3 Hz) DC

8. 8 ILIAS WG1 meeting, Hannover 23.01.2007 End mirror differential mode alignment AC Drift control (30 mHz) Autoalignment (3 Hz)

9. 9 ILIAS WG1 meeting, Hannover 23.01.2007 End mirror common mode alignment DC Drift control (30 mHz) Autoalignment (3 Hz)

10. 10 ILIAS WG1 meeting, Hannover 23.01.2007 Alignment summary Arm cavity beam pointing Uses end quadrant DC signals Quadrant position is a reference (reset at each relock) ITF alignment AC signals for all degrees of freedom Except end mirror common mode (DC signal) Absolute ITF alignment needed For repeatability of locking parameters B2 locking Beta parameter tuning (PRCL noise subtraction)

11. 11 ILIAS WG1 meeting, Hannover 23.01.2007 PR locking error signal B2_3f_ACp is used to build the error signals both for MICH and PRCL © Lisa Barsotti Demodulation at f mod / 3 f mod

12. 12 ILIAS WG1 meeting, Hannover 23.01.2007 Simple cavity misalignment (end mirror) FP end mirror misalignment => parallel shift of cavity axis. Demodulated signal: sees relative misalignment: beam vs. cavity axis AC DC position signal: sees absolute beam movement DC AC signals are independent of QD centering etc. carrier sideband

13. 13 ILIAS WG1 meeting, Hannover 23.01.2007 Possible actions

14. 14 ILIAS WG1 meeting, Hannover 23.01.2007 Where to find a common end mode AC signal No convincing common end AC signal found => Maddalena’s simulations: Only with AC alignment not controllable DC signal not satisfying No absolute reference QD position, Faraday heating beam drifts, … Correct common mode alignment not known today Possible approach Demodulate Q2 at second modulation frequency f2 Main feature: must not enter in recycling cavity Simple explanation Sidebands reflected at PR are reference for B2 beam shift => Get rid of QD shift, beam bending in Faraday etc. Like simple cavity

15. 15 ILIAS WG1 meeting, Hannover 23.01.2007 Conditions for 2 nd modulation frequency Must pass through the input mode cleaner n * 1 MHz Must not resonate in recycling cavity Easy to fulfill … Must not disturb MC lock MC lock bandwidth 300 kHz Beat frequency problems observed in the past => Avoid harmonics combinations f MC vs. f 2 < 2 MHz Should not be too far from 6 MHz Avoid major electronics changes Quadrant diode front end, demodulation board, phase shifter board Modulation index First guess: 0.03 … 0.1 (compare: f Virgo : 0.3, f MC : 0.11)

16. 16 ILIAS WG1 meeting, Hannover 23.01.2007 Frequency list < 21 MHz 3 6 7* 3132 - 1*22380 = 455 kHz 0.03 4 4 5* 4176 - 1*22380 = 1499 kHz 0.06 4 5 6* 4176 - 1*22380 = 2677 kHz 0.06 5 3 4* 5220 - 1*22380 = 1499 kHz 0.21 6 3 4* 6264 - 1*22380 = 2677 kHz 48.37 7 2 3* 7308 - 1*22380 = 455 kHz 0.22 7 6 6* 7308 - 2*22380 = 911 kHz 0.22 8 2 3* 8352 - 1*22380 = 2677 kHz 0.06 8 5 5* 8352 - 2*22380 = 2999 kHz 0.06 9 5 5* 9396 - 2*22380 = 2221 kHz 0.04 10 1 2*10440 - 1*22380 = 1499 kHz 0.01 10 4 4*10440 - 2*22380 = 2999 kHz 0.01 11 1 2*11485 - 1*22380 = 589 kHz 0.01 11 4 4*11485 - 2*22380 = 1177 kHz 0.01 12 1 2*12529 - 1*22380 = 2677 kHz 0.01 13 6 5*13573 - 3*22380 = 722 kHz 0.01 14 3 3*14617 - 2*22380 = 911 kHz 0.02 15 3 3*15661 - 2*22380 = 2221 kHz 0.03 16 5 4*16705 - 3*22380 = 322 kHz 0.06 19 0 1*19837 - 1*22380 = 2543 kHz 1.16 20 0 1*20881 - 1*22380 = 1499 kHz 0.04 20 2 2*20881 - 2*22380 = 2999 kHz 0.04 n order harmonics combination beat frq. recycling gain Beat frq. < 1 MHz Beat frq. < 2 MHz Beat frq. < 3 MHz Excluded 8.35 MHz MC modulation:22.4 MHz

17. 17 ILIAS WG1 meeting, Hannover 23.01.2007 6.26 MHz resonance condition Sideband recycled TEM01 enters FP (Anderson freq.)

18. 18 ILIAS WG1 meeting, Hannover 23.01.2007 8.35 MHz resonance condition

19. 19 ILIAS WG1 meeting, Hannover 23.01.2007 How to generate 2 nd modulation? Virgo mod. (6.26 MHz) IMC mod. (22.4 MHz) 2 nd mod. (8.35 MHz) Can we add the 2 nd modulation on the same EOM (has already 2 frequencies)? Problems with Resonant circuit Component heating Reference signal generation Question still open EOM resonant circuit

20. 20 ILIAS WG1 meeting, Hannover 23.01.2007 Conclusions

21. 21 ILIAS WG1 meeting, Hannover 23.01.2007 Conclusions We will try to add a 2 nd modulation at 8.35 MHz Virgo change request being underway Possible uses Alignment common end mirror control Locking common arm mode control (SSFS = frequency control) Presently investigating consequences Changes in electronics Modulation electronics Demodulation board Phase shifter 2 nd modulation crystal (EOM) needed? Time required for preparation, modifications, installation, tests, …? Tests foreseen next week Hopefully everything ready... seem to be tolerant

22. End

23. 23 ILIAS WG1 meeting, Hannover 23.01.2007 Alignment error signals BeamDiodeDemod.Loop Arm diff.B1pQFast Arm commonB21-Fast PRB51QFast BSB81P (tx) Q (ty) Fast (tx) Drift (ty) NIB71+2-Drift WIB81+2-Drift BMSB21P (tx) Q (ty) Drift AC signal DC signal Beam pointing control: DC signal OK. ITF control: AC signal needed

24. 24 ILIAS WG1 meeting, Hannover 23.01.2007 Alignment configurations C7 14/09 – 19/09/2005 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 WSR7 12/01 – 17/01/2007 tx BM PR BS NI NE WI WE ty BM PR BS NI NE WI WE 7 d.o.f. fast alignment; input beam and BS control XXLinear alignment XXDrift control XXLocal control XXDC error signal XXDC + AC err.sig.

25. 25 ILIAS WG1 meeting, Hannover 23.01.2007 WSR7 reconstruction matrix BMS PR BS NI NE WI WE ThetaX 0.17 0.17 B1p_q1_ACq 4 B2_q1_ACp 2 B5_q1_ACq -0.5 B8_q1_ACp -1* 1* B2_q1_DC 1 B7_q1_DC -2 B7_q2_DC 1 B8_q1_DC -1.1 B8_q2_DC BMS PR BS NI NE WI WE ThetaY -0.3 0.3 B1p_q1_ACq 4 B2_q1_ACq 2 B5_q1_ACq 0.4 B8_q1_ACq 2.3 2.3 B2_q1_DC 1 B7_q1_DC -1.5 B7_q2_DC 1 B8_q1_DC -1.15 B8_q2_DC * Filtered in Gc

26. 26 ILIAS WG1 meeting, Hannover 23.01.2007 WSR7 alignment filtering SensingFiltering DSP SensingFiltering 1 DC Filtering 2 Initial Filtering 3 Boost DSP PR tx --- Anti-3 HzOLD PR ty --- OLD End tx MODER. (for common) ---BOOST --- End ty --- INITIALBOOST--- Global control