Sheila, Kiwamu,
This is a follow up of the latest AS90 jump incident reported in 31844.
We think this anomalous behaviour started in this past Wednesday (31804). This time, we looked into some other signals and found elevated noise in SRCL, although we are still unable to localize the issue.
[Time line]
- 5:45 UTC, fully locked
- 6:02 UTC, data evaluation point #1
- 6:17 UTC, AS90 jumped and increased
- 6:30 UTC, data evaluation point #2
- 7:10 UTC, TJ manually disabled SRC1 and steered SRM to a good alignment
- 7:30 UTC, data evaluation point #3
- 9:12 UTC, another manual SRM tweek by Nutsinee
[Some observations]
The symptom is very similar to what was reported in 31804. The POP 90 increased from 13 cnts to 16 cnts. Since the AS diverter was closed, it is hard to say whether there is a jump in AS90 or not. The jump also seems to have caused misalignment in SRC1 as was the case in 31804. The first attachment is trend of some relevant signals. The leftmost vertical line in each column represents the time when the POP90 jumped. The second vertical line represents the time when TJ opened the SRC1 loop and did manual alignment. Similarly to 31804, the POP90 became noisier after the jump. The LO signals in AS36 WFSs didn't show any obvious glitch or abrupt change.
This time we looked at the spectra of the AS A 36 signals and the SRCL error signal. See the second attachment. In each panel, the blue curve is taken before the jump or at evaluation point #1 (see the above list). The green curve is taken right after the jump or at evaluation point #2. Finally the red curve is taken after TJ's fix or at evaluation point #3. I was hoping to see an obvious change in the spectra that might indicate some electronics issue, but the AS 36 signals didn't really show an obvious change as far as the spectra are concerned. However, on the other hand, we found a difference in the SRCL length error signal although this is not easy to interpret. Right after the jump the SRCL noise increased in 3 - 30 Hz by roughly a factor of two. This cannot be explained by the change in the optical gain beucase the increased POP90 should mean a lower optical gain for seinsing SRCL. Another explanation might be a worse A2L coupling contaminating SRCL due to the different spot positions on the SR mirrors.
