40m Mode Cleaner meeting

1. 40m Mode Cleaner meeting Today’s objectives • understand 40m Mode Cleaner. • compare 40m MC performance with LIGO MC performance. • have a plan to improve noise Contents • Lock status of 40m MC • Performance of 40m PSL • MC servo topology • MC open loop transfer function • MC noise Osamu Miyakawa, Caltech, LIGO Project

2. 14 hours Lock stability of 40m MC with detection mode • Lock is acquired smoothly (within 5sec). • Transition to detection mode sometimes fails. • Typical lock time: • - 20 or 30 min in daytime. • - 1 or 2 hour in night. • - Longest lock is 14hours. • Human activity around MC2 breaks MC lock out because of poor isolation of MC2 chamber. 09/12/2002 Osamu Miyakawa, Caltech, LIGO Project

3. Requirement of Frequency noise ??? Ref:LIGO-T9702518-02-D Mode Cleaner Length/Frequency Control Design Osamu Miyakawa, Caltech, LIGO Project

4. Picture of PSL • Stable and good noise performance. • Injection power to MC is 300mW. Osamu Miyakawa, Caltech, LIGO Project

5. Open loop gain of 40m FSS 09/26/2002 • Unity gain frequency=309kHz • (design : 600kHz) • phase margin=28degree Osamu Miyakawa, Caltech, LIGO Project

6. Frequency noise of 40m PSL 09/25/2002 • Frequency noise of PSL was estimated by closed FSS error signal. • Free running noise is estimated by closed FSS error signal and FSS closed loop gain. Osamu Miyakawa, Caltech, LIGO Project

7. Open loop T.F. of 40m PMC servo 09/17/2002 Osamu Miyakawa, Caltech, LIGO Project

8. 40m PMC frequency noise 09/23/2002 Osamu Miyakawa, Caltech, LIGO Project

9. Servo topology of MC Fdemod Ref:LIGO-T9702518-02-D Mode Cleaner Length/Frequency Control Design Osamu Miyakawa, Caltech, LIGO Project

10. Design open loop gain of MC detection mode • Cross over frequency=2.0Hz • Unity gain frequency=100kHz • phase margin @100kHz= 51degree Ref:LIGO-T9702518-02-D Mode Cleaner Length/Frequency Control Design Osamu Miyakawa, Caltech, LIGO Project

11. Open loop gain of LLO MC Mar 08, 2002 • Phase margin seems enough. • What limits open loop gain? Osamu Miyakawa, Caltech, LIGO Project

12. Open loop gain of LHO MC Aug10, 2002 • Why phase margin increased in cgain 20dB? • What limits open loop gain? Osamu Miyakawa, Caltech, LIGO Project

13. Measured open loop gain of 40m MC 09/13/2002 • Cross over frequency=6.7Hz (design:2.0Hz) • Unity gain frequency=32kHz • No phase margin @100kHz (design : 51degree) Osamu Miyakawa, Caltech, LIGO Project

14. Requirement for MC error signal • Closed Frequency noise estimated from MC error signal is useful to judge that MC servo is working well. • However, it is not frequency noise of MC transmitted light. Ref:LIGO-T9702518-02-D Mode Cleaner Length/Frequency Control Design Osamu Miyakawa, Caltech, LIGO Project

15. Frequency noise of Transmitted light Equation of servo topology Fa Fdemod Fp Fb ? Osamu Miyakawa, Caltech, LIGO Project

16. Approximation of Frequency noise of Transmitted light In observation band D A B C A B C D Osamu Miyakawa, Caltech, LIGO Project

17. Measured 40m MC error signal 10/14/2002 • MC error signal is not suppressed enough by low gain. • Noise is not limited by frequency noise. Osamu Miyakawa, Caltech, LIGO Project

18. Open loop noise of 40m MC error signal • Open MC frequency noise is calculated by Closed MC frequency noise, closed loop T.F. of MC and T.F. of cavity pole. • This is called as MC frequency noise, but it is actually PSL frequency noise monitored by MC. 10/14/2002 Osamu Miyakawa, Caltech, LIGO Project

19. Frequency noise of LLO MC • Why PSL out signal is used? • How is calibration below Cross over frequency ? • --It should be calibrated by MC gain (not VCO loop gain). • How is effect of MC cavity pole? • Why the difference exists between analog and digital? Osamu Miyakawa, Caltech, LIGO Project

20. Summary • More open loop gain of MC servo. • More phase margin. • Starting noise hunting. Osamu Miyakawa, Caltech, LIGO Project