KAGRA Logbook

MIF (ITF Control)

masayuki.nakano - 16:37 Tuesday 26 September 2023 (26902)

PRFPMI can't be locked due to bad diagonalization of the ETMX actuators

[Ushiba, Capote, Nakano]

We tried to lock the PRFPMI, but we found that the ETMX has totally different actuator response from the one measured in August, due to warming up from 30K to 220K. That would cause the 0.7Hz oscillation and can be predicted to have many other problems. So, we decided not to keep trying it, but to start the re-diagonalization script before further trial.

Activity log

1010 Found that the BIO setting of ETMY was wrong. The TM input is switched to the test input. This was for Q measurement, and we forgot to bring it back. We restore it and check all other suspensions as well.
1019 Measured the ETMY actuator response with the ALS DARM, locking only ALS CARM. The actuator response was the same as in August.
1030 Earthquake
1200 We found the BIO setting is not causing the 0.7Hz oscillation. We still have the same issue as yesterday, we can't hold at ALS_DARM due to the 0.7Hz oscillation. We can't lock
1508 Try 0.7Hz lead filter implemented into ETMY LOCK filter. No good.
1514 Try 0.7Hz lead filter implemented into ETMX LOCK and ETMY LOCK filter. No good.
1518 Try 0.7Hz lead filter implemented into ETMX LOCK filter. No good.
1605 Measured the ETMX actuator response of the TM stage with the ALS DARM, locking only ALS CARM. We found the actuator response has changed from August. Seems to have a big change at 0.6Hz peak and 1-2Hz structure.
1605 Measured the ETMX actuator response of the IM and MN stage with the ALS DARM, locking only ALS CARM. Big difference, and we feel we need to re-diagonalize the actuators.
1630 Start diagonalization script.

Comments to this report:

Elenna Capote - 20:35 Tuesday 26 September 2023 (26919)

Ushiba-san is writing a klog describing the successful work in diagonalizing the ETMX drive.

Once the drive was diagonalized, we checked the transfer function from the ETMX and ETMY L test points to ALS DARM. This transfer function helps us compare the relative drive strength between ETMX and ETMY (see attached plot). We calculated that we needed to adjust the gain of the ETMY L lock filter by -2 dB to account for the minor difference between the two suspension drives. This gain is in the ETMY L lock filter bank in FM2 as "gain-2dB".

With the properly diagonalized drive, we were able to achieve the ALS DARM lock using both ETMX and ETMY. From there, we could engage PRMI 3F LOCKED. We watched the POP 90 signal, and noticed it did not increase beyond about 0.6 (arbitrary units). We think this should be able to converge closer to 1 if the alignment is good. However, we continued on from there anyway.

Next, we achieved PRFPMI LOCKED with 3F signals. This was successfuly and there was no issue with the handover to IR. Next, we successfully transitioned to 1F signals. We tried proceeding to ENGAGE PRFPMI ASC. The buildup of POP 90 improved to above 0.9. All the alignment signals moved significantly. While we were waiting for the alignments to settle, there was a very fast ring up of 34.5 Hz present in the LSC signals. We think this could be the DARM loop. I think we should measure the OLGs of all the length loops at next opportunity. We are choosing to stop here for now, and we will pick up this effort in the morning.

Images attached to this comment

26919_1695728012_Screenshot from 2023-09-26 20-27-43.png

tomotada.akutsu - 22:13 Tuesday 26 September 2023 (26922)

Thanks, good to hear PRFPMI has come back somehow!