I measured MCE suspension TFs.
Figure 1-7 show the results.

Pitch gain is lower than before while yaw gain is higher, which might be due to the centering of OpLev QPDs.
Also, coherence at high frequency is not good, which implies that suspension rubbing slightly.
we need visual inspection and fix the problem.

I went to the visual inspection of the MCe suspension again. I could not find any rubbing points in the IM as well as in the TM. Though one EQ stopper (HR upper) was closing to the TM (~1mm), it did not touch the TM.

[Takahashi, Washimi]

We went to the visual inspection again.

• Lifted the magnet box (IRM) completely to see the side of the IM. We could not find any causes of the rubbing.
• Some screws for the wire clamps look SUS made (not yellow/brown). Though we tried to attach a small magnet to the screws, the screws were not magnetic.
• The TM has rotated in yaw in CCW after lifting the IRM. We could correct the yaw rotation by twisting the TM by hand. The TM pendulum was easily formed in yaw.
• Measured the TFs (/users/VISsvn/HealthCheck/MCE/arxiv/2024/02/). The actuation by the H2 coil was too small. One bottom stopper was touching the TM. The TF with the H2 actuation was improved after releasing the stopper. The other TFs should be measured again.
• The IRM is still lifted.

I measured MCE H1 TF with current condition (IRM is lifted up).
Figure 1 shows the result.

Coherence is good except for the resonance of the suspensions, so it looks healthy with this condition.
After IRM is back to the nominal position, we need to check the TF again.

Note:

Initially, coherence at high frequency is not good because suspension shakes too much and many non-linear couplings can be seen.
So, I put several notches at excitation signals not to kick the resonances too much (fig2) and then obtained healthy TF.
I checked the suspension motions during the TF measurement yesterday and found that suspension moves very large, especially in yaw (fig3), which might cause non-linear couplings.
Since we don't change excitation amplitude from the prevous health check, It might be due to the change of actuator magnets, which have larger efficieny now.
So, it is probably necessary to adjust the excitation amplitude to obtain enough large but not too much suspension motion.

Well, do we have information the magnetometer's readout for the magnets before and after the replacement regarding MCe???

Finally, we obtained healthy transfer function of MCE, so MCE seems healthy now.

I remeasured MCE TFs with new template files after moving IRM back to the nominal position (klog28492).
Figure 1 - 7 show the results.

All TFs have good coherences and TF shape is almost same as before.
So, MCE suspension seems healthy now.

Followings are some note on the results.
* L2P and L2Y coupling seems change but it might be solved by actuator balancing, hopefully.
* Overall gain increased about 9 dB due to the change of magnet size.
* Somehow, pitch resonances are slightly higher than before. I have no idea why but it doesn't seem a serious problem.
* Actuator efficiency variation of each coil-magnet actuator is about 3 dB.

Result of final health check of MCE.
Since beam spots on QPDs are far off from the center and out of linear range now, it ishard to say the low coherence is coming from some suspension trouble or just low S/N duing the measurement.

Remeasurement after moving MCE with respect to the opLev QPD center.
Coherence becomes better and TFs look healthy.