Last Friday, I was mainly searching for the 6.18Hz in the HEPI and ISI actuators/sensors. There was no real conclusion from the study except that the 6.18Hz was not coming from HEPI and it was visible mainly in the vertical degrees of freedoms.

Then, the SUS was suspected. Few tests were done:
- The damping loop and the coil drivers were unplugged. The 6.18Hz didn’t show up in the ISI spectra.
- The coil drivers were re-plugged. The 6.18Hz didn’t show up in the ISI spectra.
- Then, the damping loops were turned on independently. It appears that main chain damping loops using the left and right OSEMs create the vertical motion at 6.18Hz. Then, this motion is transmitted to the ISI and spectra show a 6.18Hz feature.

Two MO OSEM sensor spectra are presented in attachment. In both cases, the ISI is isolated.
- Without SUS Damping (first figure)
- With SUS Damping

J.K and A.P are taking open loop transfer functions.

During the hunt, I saw some excess noise on R0 OSEM RT