Today' shift focused on checking the reproducibility of yesterday's long lock (54067) and to further check the influence of SR misalignment on the SDB1 and SDB2 quadrant signals.
Three locks at CARM offset zero were achieved:
- 9.15-9.40 UTC, ~25 minutes long, a small tuning of SR TY (0.6 rad) was performed and triggered a large improvement in the dark fringe stability and level at 9.18 utc (see figure 1 and 2). A sudden ~85 Hz oscillation noticeable on DARM and DIFFp TY led to the unlock (figure 3).
- 11.26-11.38 : the engagement of SSFS and the 1f handoffs of PRCL and MICH were tested successfully during this lock. In the second part of the lock the alignment of SR TX was moved in steps of 0.2 rad each (see figure 4).
- 12.45-12.58 : further misalignment steps of SR were tested in this lock, both in TX and TY (see figure 5 and 6)
Further attempts failed due to difficulties in engaging the lock of the CITF in the afternoon.
Some notes on the SR misalignment steps and CARM offset zero behaviour:
- In today's locks, no clear effect of the SR misalignment was noticed neither on the SDB1 LC (closed on the SDB1_B5_QD2 DC quadrant) nor on the SDB2 56MHz quadrant signals (see figure 2-6). This is in opposition to what observed in yesterday's long lock (see figure 7) and in the 30th november locks (54061 ). The reason of this change of behaviour is still under investigation.
- In the first lock, the SR alignment change 'triggered' a (lately recurrent) sudden change in the ITF behaviour. This effect has been observed several times in the past days too, and often happens a couple of minutes after reaching carm offset zero without any particular operation triggering it (e.g. today at 12.46.20 UTC, see figure 8). The usual features of this behaviour change on many signals, including the following:
- on B1p, B4, B7, B8 DC signals
- on the B1p and B5 galvo and quadrant signals,
- beam shape observed on cameras and phase cameras
- DARM error signal and correction spectra (this also leads to an offset change on the test mass AA centering signals obtained from demodulating the dithering lines from the DARM correction sent to the input mirrors)
- DIFFp error signals
- a reduction of slope of the B4_12 and B4_112 MHz signals
- sidebands balance
Additional operations performed:
- The engagement of the SDB1 drift control using the LC_B5_QD2_enbl relay has been added in the automation in DRMI_LOCK.py. It is now automatically engaged once the 3f handoff of the CITF is performed, and it is disabled in the DOWN state.
- The demodulation phase of B2_169MHz (used for MICH and SRCL) has been reduced by ~0.5 rad in the 160mW and 480mW locking steps, in order to avoid unlocks during the CARM offset reduction procedure.
The ITF was left in DOWN state in order to proceed with the TCS calibration activities.