To we worked on the BS alignment loop; the idea is to move from the current control scheme to a new one, based on the new B1s_QD1_50MHz signals.
The current control scheme is:
- TX: BS_BL_B4_6MHz: blending between B1p_QD1_50MHz_I (low-passed) at low frequency and B4_QD1_6MHz_I at high frequency (high-passed)
- TY: B1p_QD2_50MHz_I (low frequency), which is sent to the DSP where the blending with the OpLev at high frequency happens.
This is the sequence of the tests we made, in different locks, all on the TX DoF, since it is the less robust one and the one most easily tweakable:
- we replaced the whole signal with B1s_QD1_50MHz, intercalibrated at low frequency with the low frequency weight (sensing weight = 0.207) (we didn't use it, but for reference the weight for TY is 0.11): at 14:29:15 UTC we made the handoff in drift control, around 14:38 (briefly) and then again 14:30:30 we tested in full bandwidth, but we unlocked; not because of the 1.2 Hz oscillation, but some other disturbance, that could be also seen by PR_TX
- we used the usual signal, but increasing the blending frequency by increasing the gain of the low frequency branch: 15:28:52 UTC B1p gain 2x in drift control, 15:29:23 UTC full bandwidth, shortly followed by the unlock;
- we replaced only the low frequency branch with B1s_QD1_50MHz with the overall same calibration as B1p_QD1_50Hz: full bandwidth test just before 16:22 UTC, quickly reverted before unlocking.
All data will be analyzed offline, but in all tests the coupling with PR_TX looks the one thing which is the most impacting the full bandwidth loop.
After that, several lock acquisitions were tested, undisturbed both in terms of acquisition and steady state; we also moved to LOW_NOISE_3_ALIGNED without having to change anything (same power as in the past, just reduction of lines and noise there). The locks do not last much, and they sometimes look very glitchy, at least by looking at Hrec. In any case, Hrec itself looked glitchy and some data was missing. Also in this case, we will look at data offline.
Regarding the recent automation of the input power increase, that worked very well, but we gained one case to study: after an unlock, INJ_MAIN went into the INJ_FAULT state around 18:51 UTC.