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MIF (General)

tomotada.akutsu - 20:23 Thursday 06 April 2023 (24703)

Looking back when 127.3 Hz started to appear in IMMT1 trans pitch

Summary

With pastavi, I tried to know since when the 127.3 Hz stable peak has appeared in IMMT1 trans pitch to consider how to damp it in the future. Works on Jan 17 2022 JST (19489) seems related(?), but anyway we may need more studies...

Details

In the future, we will need to damp 127.3 Hz peak (or sometimes written as 128 Hz) found both in DARM and IMMT1 trans pitch; according to the studies in the past, this peak would be due to something in the IFI chamber. See 24308, 24396 and 24487.

According to 24291, this peak is observable even without the main interferometer and even when the relevant vacuum chambers being opened. So it may be possible to go back to the past to see when this peak started appearing, and I found a candidate timing when the phase transition happened; at the day time on Jan 17 2022 JST.

Figs. 1 and 2 are reference; they shows IMMT1 trans QPD pitch before that day; on Jan 14 and 16. There are no apparent 127 Hz peak.
Fig. 3: Jan 17 03:00-05:00 UTC; still no such peak.
Fig. 4: Jan 17 04:00-06:00 UTC, so the first 1 hour is overlapped with Fig. 3; still no such peak.
Fig. 5: Jan 17 05:00-07:00 UTC, so the first 1 hour is overlapped with Fig. 4; around 06:10 UTC, after a shock, the peak has seemingly started.
Figs. 6 and 7: afterward; since then, this peak has been there.

Assuming this analysis would be true, looking at the klog on the relevant timing (19489), it seems STM2's mirror holder was 90-deg rotated to avoid beam clipping, and also it was moved slightly. So clamping it is matter?? cabling (of even STM1)?? I have no idea so far....

For confirmation whether the QPD was properly illuminate at that time, I checked the SUM of this QPD; see Fig. 8. It is about 20000 counts, and at that time about 3 W was from IMC. Currently, 1.1 W from IMC and the sum is around 7300 counts. 1.1/7300 * 20000 = 3 W, so it would be consistent.

Images attached to this report

24703_1680777766_1326207618_1326207738_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680777768_1326380418_1326380538_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680777771_1326423618_1326423738_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680777774_1326427218_1326434418_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680777778_1326430818_1326438018_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680777783_1326441618_1326441738_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680777785_1326466818_1326466938_K1 IMC-IMMT1_TRANS_QPDA2_DC_PIT_OUT_DQ_Spectrogram.png

24703_1680780108_1326380418_1326384018_K1 IMC-IMMT1_TRANS_QPDA2_DC_SUM_OUT_DQ_TimeSeries.png

Comments to this report:

tomotada.akutsu - 10:10 Friday 07 April 2023 (24707)

Additional observation.

It is interesting that the strong peak at around 150 Hz disappeared around almost the same (imaging the time span of the site work at that time) timing when the 127 Hz peak started to appear. Was this due to relocation of STM2????

tomotada.akutsu - 11:57 Friday 07 April 2023 (24711)

This is a memo for work candidates to be done immediately after O4a.

The attached photo was taken on Sept. 13 2022, and the same one as Fig. 1 of 22084.The same information can be extracted from Fig. 2 of 20233 (this was on Mar. 25 2022) as well. Looking at these photos, though as a hindsight, the way to fix the STM2 pillar seems weak especially in the pitch direction: the foot flange is partly out of the top surface of the optical table, and two clamps are in line; moreover or first of all rather, the usage of the two clamps themselves are worng; they should have not been used like this. With this, the contacting is not by surface but lines, unfortunately. Hope sufficient accessibility.
Interestingly, we had checked the rigidity of the STM2 (and 1) structure in the IFI chamber the other day (on Mar. 28 2022) by hands (see 20259). So they would be enough rigid for hands.

Maybe, after O4a, one candidate of works would be to open the K400 flange in the minus Y direction of the IFI chamber to access the foot flange of the STM2 pillar, and at least add another clamp there. If possible I'd like to also open the minus X side to replace the currently-installed wrongly-used two clamps, but that would mean the vacuum pipe connecting the IFI chamber and the large GV should be detached, which would pay much...

Anyway, going back to my original proposal, if we will detach the REFL window, the same procedure to deal with the final beam dump for ghost beams from the REFL window should be also taken into account. See 22244.

Images attached to this comment