[Ushiba, Aso, Akutsu, Takano]
We finally recovered FPMI for the first time in 2 weeks.
What we did today
Check of stability of CARM loop
We measured OLTF of CARM loop of
We measured OLTF of CARM loop of
- ALS only
- ALS and IR
then reconstructed IR only by calculation. From this measurement we confirmed that IR CARM loop is stable by itself and 40dB attenuator was too much. Now the attenuator is left removed.
Fig.1 measured and reconstructed OLTF of CARM loop
Adjustment of DARM loop gain
After DARM hand off it seemed that DARM is still noisy to lock cavities stably, so we made the gain of DARM loop as big as possible. Finally we increase the gain by 4 times.
After DARM hand off it seemed that DARM is still noisy to lock cavities stably, so we made the gain of DARM loop as big as possible. Finally we increase the gain by 4 times.
CARM hand off trial
After that adjustment, we succeeded in hand off CARM signal stably. It seemed that the instability of locking came from lack of DARM control gain.
Transition of MICH signal from 51MHz to 17MHz
Next step is transition of MICH signal from 51MHz to 17MHz of REFL PDA1. We did swept sine measurement and decided the relative gain btw 51MHz and 17MHz. Using thea value, FPMI was fully locked.
After the first success, we modified the filter condition and reconstructed OLTF as 2 weeks ago. Now OLTFs of DARM and MICH loop are the same as before. For CARM it is impossible to measure overall OLTF because the control loop of CARM contains a fast path (analog circuit).
Fig.2&3 OLTF of MICH&DARM. blue: 2 weeks ago, red: today
