Rana, JeffK, Kiwamu,
We did some maintenance items on IMC ASC. The major activities are:
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We had a difficulty in restoring the IMC alignment back as we ran the offloading script when the HEPIs were down and therefore we screwed up the alignment.
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Interestingly, restoring the suspensions using the witness sensors as references did not work at all. Simply burt-restoring the suspensions and ASCIMC frontends brought it back to a good lock-able alignment.
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After the recovery, we ran the offloading script again and so all the MC suspensions now should be in good alignment.
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We set a limiter in each loop with a hope that this is going to reduce a risk of tripping the suspensions (alog 16138, 16128) . Here are the counts we set for the limiters:
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DOF_1_P(Y)_LIMIT = 125
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DOF_2_P(Y)_LIMIT = 125
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DOF_3_P(Y)_LIMIT = 250
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DOF_4_P(Y)_LIMIT = 3000
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These values are derived such that they are roughly the same as their 5 sigma deviations in 100 days trend except for the DOF4 loop which had hit the new limiter once in this evening. So we set the DPF4 to a high value.
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We disabled the 2nd whitening stage in MC2_TRANS QPD because the signals were saturating most of the time when IMC was not locking.
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Therefore the MC2_TRANS QPD now has one whitening filter.
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We cleaned up the control filters and installed a new low-pass in every DOF. Rana will report some more details about this.
Also, tomorrow or sometime this week, we might insert a lens in the REFL gigE path as the REFL beam now is a bit too big to be able to cover the spatial higher order modes.
Some issues with the current implementation:
Tonight we have twice had MC lock losses where MC1+MC3 got completely misalinged, although they didn't trip. The second one of these was at the same time as a lockloss of the ALS, but we don't know if the IMC caused it or ALS. This was at 6:35 UTC, Jan 21st.
We made the decision not to increase the spot size. This was done at LLO to decrease the jitter coupling into the ISS. The in-vacuum ISS doesn't require this.
The IMC seem to have worked much more reliably, before we added DOF4. Please turn it off for good.