Oshino, Nakagaki, Yamamoto, Sawada, Tanaka (Onsite), Miyoki, Miyakawa, Ikeda (remote)

## Abstract

We recovered IFO to the OBSERVING state after resolving the timing system trouble.

## What we did

First of all, we requested the LSC_LOCK guardian to go to the OBSERVTION state but the PRMI alignment seemed to be too bad to lock PRMI since the POP90 power is too low and TEM10 was mainly observed with POP S-pol camera. So we performed INITIAL_ALIGNMENT.

After the initial alignment, we retried to lock IFO. HANDOVER from ALS to IR was succeeded but the lock was lost as the trans. power gradually lowered whenever the ASC_LOCK guardian was in the INCREASING_SOFTHARD_GAIN. Fig.1 shows the timeseries of ARM ASC error/feedback signals around the lockloss. DHARD Y error signal (K1:ASC-DHARD_Y_IN1_DQ) went far from 0 in engaging ASC. I suspected the sign flip of the control at first. I tried to flip the sign by implmenting "-1" gain in FM9 of ASC-DHARD_Y, which is an empty originally, but the situation was not changed. 

Then, we found that there are no outputs in IX/IY TM coils (ex. K1:VIS-ITM{X,Y}_COILOUTF_H1_OUTPUT in fig.1) even though the ASCs were already engaged. And we found that ISCWDs of ITMX and ITMY(ex. K1:ITM{X,Y}_TM_ISCRAMPHOLD_STATE = 1 in fig.1) were activated. Unlike ETMX and ETMY ISCWDs, ITMX and ITMY ones seems not to be deactivated automatically. Anyway we deactivated them. After the deactivation, their ASC feedback signals was being outputted to their coils and ASCs worked well (fig.2).

After that, IFO reached the OBSERVATION state. At last, Sawada-san turned on the OBS_INTENT flag around 15:22 JST in klog34330

Now, FM9 of ASC-DHARD_Y is not used. I already reported the change of the filter bank to Yamamoto-san and he accepted the change.

## Note

ITMX and ITMY ISCWDs seems to be activated from this moring maybe due to the reboot work of IX and IY (fig.3). Are these WDs always deactivated basically?