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Virgo Runs (C9)
casanueva, derossi - 17:08 Monday 21 May 2018 (41492) Print this report
Analysis of the unlocks during the run

This morning we have made a preliminary analysis of the cause of the unlocks that took place during the weekend. We have excluded the period when Eric went to the laser lab due to the excitation of the suspended injection bench (see entry 41464) and the period of troubleshooting after the problem with the DAQ (see entry 41467) and the manual unlocks.

We have divided the unlocks in two groups, the ones occurred during the lock acquisition and the ones occured when in Low Noise 3.

LOW NOISE 3
08.32.42 UTC / May 19 Fast Unlock
11.52.25 UTC / May 19 Fast Unlock
14.35.43 UTC / May 19 Fast Unlock
16.42.07 UTC / May 19 DARM? Saturation on B1 DC?
21.27.14 UTC / May 19 Fast Unlock
22.25.37 UTC / May 19 Fast Unlock
22.50.56 UTC / May 19 DAQ
11.35.48 UTC / May 20 Fast Unlock
15.02.38 UTC / May 20 SSFS oscillation @ 2kHz
20.39.09 UTC / May 20 Fast Unlock
22.47.01 UTC / May 20 DAQ
00.25.00 UTC / May 21 SSFS oscillation @ 2kHz

This morning we made a "Fast Unlock" manually from Low Noise 3, in order to compare it with the ones of the weekend 12.18.32 UTC.

Time ITF_LOCK_index Cause
08.42.35 UTC / May 19 123 125 Hz oscillation on DARM
09.19.27 UTC / May 19 119 SSFS high gain when going to DF
14.38.56 UTC / May 19 40 West arm locked in a HOM
14.45.35 UTC / May 19 119 SSFS high gain when going to DF
16.49.42 UTC / May 19 103 ???
16.52.21 UTC / May 19 90 Fast Unlock
16.56.13 UTC / May 19 81 IMC unlock (misalignment)
17.02.48 UTC / May 19 123 IMC unlock (misalignment)
17.25.59 UTC / May 19 126 DARM 27 Hz - saturation?
17.39.20 UTC / May 19 126 DARM 27 Hz - saturation?
21.34.11 UTC / May 19 119 SSFS high gain when going to DF
11.49.05 UTC / May 20 119 SSFS high gain when going to DF
15.08.21 UTC / May 20 40 Fast Unlock
15.22.53 UTC / May 20 91 Fast Unlock
15.23.51 UTC / May 20 39 Fast Unlock
22.58.45 UTC / May 20 126  DARM 27 Hz - OMC? saturation?
23.02.28 UTC / May 20 102 DAQ

From the analysis we made it is interesting to remark that once in Low Noise 3 the most common cause of unlock comes from the IMC. Instead during the lock acquisition we have experienced a wide causes of unlocks (without counting the punctual problems mentioned at the beginning). One well understood is the high gain of the SSFS when reaching DF, we need to adjust better this transition.

We marked in yellow the unlocks that are not yet understood, we will keep on investigating. Also we will keep on studying the Fast unlocks to try to find a cause.

Comments to this report:
derossi - 17:26 Monday 21 May 2018 (41494) Print this report

the unlocks on may 19, from 16:42 to 18:20 UTC are due to the excitation of the EIB, as shown in the attached plot.

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bersanetti - 10:44 Wednesday 23 May 2018 (41525) Print this report

The unlocks due to DARM oscillating at 27 Hz are caused by the fact that lately, even if OMC1 locks at the same B1s2 power ~ 1.5 mW, the intercalibration between RF and DC readout has changed and DARM falls down to the lower end of the stability region and sometimes unlocks at this stage. This has been cured for the time being by changing the DARM gain at the same time of the hand-off of the error signal; however, since the same change of the gain happens in the opposite way a bit earlier in the lock acquisition, it makes more sense to recalibrate the DC error signals, which should only make the final DARM gain to be changed and the DC readout lock acquisition smoother.

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