1. Takanori Sekiguchi External Review Alignment control servo for type-B/type-Bp (OpLev/WFS) 1 T. Sekiguchi

2. Takanori Sekiguchi External Review Overview 2 OSEM damping controls are not allowed to be switched on during the observation phase, in terms of control noise couplings Thence alignment control should rely on oplev and WFS. Oplev is used during/just after the lock acquisition phase and then gradually the control will be shifted to controls using WFS. We want to use actuators on IM since they have larger range. Another possibility is having hierarchical controls using IM&TM actuators. To achieve requirement on noise coupling from WFS, UGF should be set around 1 Hz.

3. Takanori Sekiguchi External Review Control using IM actuators 3 Put two zeros at a certain frequency to compensate 180 o phase delay. Then the response looks like normal pendulum’s. Design servo filters, having enough gains below 0.1 Hz and low gains above 10 Hz to mitigate noise coupling

4. Takanori Sekiguchi External Review Actuator responses 4

5. Takanori Sekiguchi External Review Yaw 5 Compensation with zeros at 1.2 HzServo

6. Takanori Sekiguchi External Review Yaw 6 Open Loop Total Servo

7. Takanori Sekiguchi External Review Pitch 7 Compensation with zeros at 0.7 HzServo Precise Notch with Q~1e3, Depending on actual Q

8. Takanori Sekiguchi External Review Pitch 8 Open Loop Total Servo

9. Takanori Sekiguchi External Review Pitch noise 9

10. Takanori Sekiguchi External Review Control succeeded in prototype 10 Pitch Yaw Red: Open loop gain, Blue: Closed-loop actuator response

11. Takanori Sekiguchi External Review Servo Filter design in prototype 11 Pitch Yaw Notch Q=50 * Need to compensate low pass in oplev driver @15 Hz

12. Takanori Sekiguchi External Review Problem 12 Feedback using servo with high-Q notch filter is not robust, since the control gets unstable with slight change of the system. In prototype, the control gets unstable when TM is locked to a photo-sensor (which mimics the signal of interferometer) We can change notch frequency after lock acquisition, maybe… It’s not a smart solution, though. RM pitch resonance Q should be reduced.

13. Takanori Sekiguchi External Review Q reduction of RM pitch mode 13 In actual system, RM pitch mode has lower frequency (~3.5 Hz), due to material change from tungsten to steel and thickness reduction from 0.6 mm to 0.55 mm. This makes situation even worse. How to reduce Q?