1. Alignment status & plans

2. 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

3. 2nd fmod layout
WSR10 alignment layout
6.26 MHz
8.35 MHz

4. 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

5. 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

6. 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 Hz ?!
B8_q1
B8_q2 B8
10 Hz
before
after
(high ISYS noise!) WE
B7_q1 WI PR NI NE
B7_q2 BS B7

7. 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)

8. 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

9. 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)

10. 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

11. 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, …

12. 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

13. 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

14. End

15. Alignment configurations
tx IB PR BS NI NE WI WE
ty IB PR BS NI NE WI WE
10 d.o.f. fast alignment
WSR /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
WSR /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.

16. WSR10 sensing matrix BMS PR BS NI NE WI WE ThetaX 0.5 B1p_q1_ACq
B2_q1_ACp
B5_q1_ACq
B8_q1_ACp
B2_q1_DC
B7_q1_DC
B7_q2_DC
B8_q1_DC
B8_q2_DC
BMS PR BS NI NE WI WE ThetaY
B1p_q1_ACq
B2_q1_ACq
B8_q1_ACq
B2_q1_DC
B7_q2_DC
B8_q2_DC
* Filtered in Gc sensing

17. 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

18. 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

19. 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