Virgo Logbook

The goal of the morning and afternoon shifts was to perform small steps NI DAS powers in order to reach and have a more stable lock in LN2.
At 07.25 UTC, we checked and restored the CHs powers to the nominal values.

Before STEP I, the situation seemed to be improved in terms of SBs balance with respect to yesterday evening, so it was possible to reach LN2, but the lock was not really stable mainly because of a drift in the SDB1 position.

At 10.27 UTC NI DAS IN and OUT have been switched on for STEP I. The power values are reported in the table below.

	Step I 10.27 UTC	CH [W]	INNER DAS [W]	OUTER DAS [W]
W	on the ITF	0.036	0	0
W	on the pickoff	0.221	0	0
N	on the ITF	0.024	0.05	0.1
N	on the pickoff	0.147	0.008	0.016

Also in this condition, we reached LN2. The situation of the SDB1 drift seemed to be improved, BS_TY_SET_SERVOLOOP was disabled and the BS parameter was manually adjusted in order to improve the alignment and the optical gain.

In the afternoon part of the shift, two more NI DAS steps were performed. The values are reported in the following tables.

	Step II 18.23 UTC	CH [W]	INNER DAS [W]	OUTER DAS [W]
W	on the ITF	0.036	0	0
W	on the pickoff	0.221	0	0
N	on the ITF	0.024	0.05+0.05=0.1	0.1+0.1=0.2
N	on the pickoff	0.147	0.08+0.08=0.016	0.016+0.016=0.032

STEP II didn't show clear changes in the ITF stability (LN2). We decided to perform a further step, reported below, which effects will be investigated tomorrow morning.
More details about the evolution of the ITF figures of merit are reported in entry 62286.

	Step III 20.28 UTC	CH [W]	INNER DAS [W]	OUTER DAS [W]
W	on the ITF	0.036	0	0
W	on the pickoff	0.221	0	0
N	on the ITF	0.024	0.1+0.1=0.2	0.2+0.2=0.4
N	on the pickoff	0.147	0.016+0.016=0.032	0.032+0.032=0.064

At 12.30 UTC PR CHRoCC has been switched on at 0.08 V and switched off at 15.21 UTC.