KAGRA Logbook

MIF (General)

dan.chen - 16:42 Thursday 12 February 2026 (36337)

IFO Recovery before ASC Work

[Kenta Tanaka, Dan Chen]

Before starting ASC work, we recovered the IFO since it had not been locked for several hours. We aimed to bring it back to the RF LOCKED state and record the alignment.

After performing the initial alignment, the lock process got stuck at FIND_IR_RESONANCES.

We investigated this state in detail. Eventually, Kenta manually went through the related calculations, which led us to identify the cause: FM1 of K1:ALS-SUM_OFS_SLOWOUT_CALI was ON. This made the sweep behavior inappropriate and prevented the state from exiting properly.

After turning FM1 OFF, FIND_IR_RESONANCES was successfully passed.

Lesson:
It took 3–4 hours to track this down. If changes are made to the IFO configuration, please restore them afterward.

Images attached to this report

Comments to this report:

takafumi.ushiba - 20:56 Thursday 12 February 2026 (36339)

>Lesson:
>It took 3–4 hours to track this down. If changes are made to the IFO configuration, please restore them afterward.

It's my fault. Sorry for forgetting to revert the filter setting.

kenta.tanaka - 1:17 Friday 13 February 2026 (36341)

After that, IFO could not reach RF_LOCKED state because transmission powers decreased when ASCs were engaged, unfortunately.

I stopped LSC_LOCK from engaging ASC by requesting ENGAGE_WFS_DC. Then I engaged ASCs one by one. I found that DSOFT Y error signal moved far away from 0 when DSOFT Y was engaged. (fig.1)

I attempted something to solve this issue, flipped the sign and offloaded the offset in DSOFT_Y_A. However, I failed to solve it by these attemption. At last, I restored the input matrix value. Then, IFO was suceeded in reaching RF_LOCKED state. Therefore, the input value in klog36329 seems not to be reproducibility, unfortunately.