Draft report in progress; it will be finalized and convalidated at the end of the shift.
ITF found in Science mode.
Software
Following the issue on ALS flip mirror in the early morning (Entry 64161), 2 new flags have been implemented for the DMS in order to monitor them. Configuration inside the VPM process have been done and will be reload during Tuesday maintenance to be made effective.
Tuesday 30th of April a slow cold FSR scan has been performed (LOGBOOK n°64135). Here is the report of the analysis concerning the estimation of the finesse of both north and west Fabry-Perot cavities. On each of the 12 FSR scans, an Airy peak has been fitted. From those fits, the FSR and the width at half maximum have been estimated allowing us to derive the finesse. Then we took the average of all the results. Values obtained for each cavities are summarized below :
B7 : average finesse 463.16 standard deviation 2.99
B8 : average finesse 447.59 standard deviation 4.04
Figure 1 shows one example of fit for both north and west scan. For each example, the fit is shown on the full scan and zoomed on the first TEM00 mode. As it can be seen, the data are very noisy. Nevertheless, this can not explain why results are asymmetric between north and west cavities.
Here is the quick analysis of the OMC lock and scan performed by the operator during the last maintenance:
https://logbook.virgo-gw.eu/virgo/?r=64135
Fig.1 shows the OMC lock. We reach about 13.7 uW of power on B1_PD3 when the OMC is locked on the carrier TEM00.
Fig.2 and Fig.3 show the OMC scan in temperature. The first order mode peak is about 14% of the TEM00 peak, which is not a very good alignment (this means that the offsets used for NI single bounce are not well tuned), but sufficient for this type of sanity check.
One of the reason for having a CARM SLOW control is the OMC. If there are fluctuations in CARM the OMC length needs to follow, and with higher CARM fluctuation the OMC lock RMS will become worse and increase the thermorefractive coupling. However, this is seems to be very far from limiting.
Figure 1 shows the current noise budget (May 3 early afternoon), and the magenta line is the OMC length noise projection. about a factor 100 below the sensitivity curve.
Figure 2 shows last night when the ground motion was large (and presumably CARM RMS worse), the OMC length noise projection is still about a factor 20 below the sensitivity curve.
Figure 3 before the reduction in the CARM SLOW loop gain the OMC length noise projection was so low that it did not show on the figure.
So my impression is that if needed the CARM SLOW loop gain could be reduced by another factor 2. But there might be other aspects of the interferometer than the OMC that require a low CARM RMS.
The ITF kept the lock all the shift, from 5:00UTC the sensitivity started to worsening and the BNS range went down to 35Mpc, this is because of at the relock the end green beams was not flipped out, I did it by hand to recover the standard sensitivity, science mode stopped from 5:13UTC to 5:17UTC.
Sub-system reportsAir Conditioning
eurothermServer2 stopped and restarted at 7:58UTC because of missing data from FCEM air conditioning system.
Other
FCEM_MotSwitch crashed and restarted at 8:30UTC.
Yesterday the gain of CARM SLOW has been reduced by almost a factor of 2, in order to restore its normal stability, but obviously also its accuracy has been reduced. I looked for recent data with similar seismic, suspension and TMs motion (fig 1, fig 2); RFC error signal with the two different gains is compared in fig 3. The required accuracy is not clear to me: having a number, we could design a proper filter. We need also to take into account the noise projection of this loop towards Hrec. The noise injection performed yesterday has been analysed: we can see in fig 4 that at 20 Hz the projection is a bit too close to the sensitivity (DARM is totally limited by this noise in a wide region - fig 5). With the gain used in the past days, the projection would become too close, so an eventual request of more accuracy would require a better shaping of the control filter, or a better noise subtraction.
One of the reason for having a CARM SLOW control is the OMC. If there are fluctuations in CARM the OMC length needs to follow, and with higher CARM fluctuation the OMC lock RMS will become worse and increase the thermorefractive coupling. However, this is seems to be very far from limiting.
Figure 1 shows the current noise budget (May 3 early afternoon), and the magenta line is the OMC length noise projection. about a factor 100 below the sensitivity curve.
Figure 2 shows last night when the ground motion was large (and presumably CARM RMS worse), the OMC length noise projection is still about a factor 20 below the sensitivity curve.
Figure 3 before the reduction in the CARM SLOW loop gain the OMC length noise projection was so low that it did not show on the figure.
So my impression is that if needed the CARM SLOW loop gain could be reduced by another factor 2. But there might be other aspects of the interferometer than the OMC that require a low CARM RMS.
ITF found in Science Mode (LN3_SQZ).
At 02:53 UTC ITF unlocked for unknown reasons (TBC). Relocked at first attempt at 03:43 UTC. Science Mode set.
Guard Tour (UTC):
21:30 - 22:00
23:52 - 00:23
02:00 - 02:30
03:25 - 03:55
The activity of today was two-fold, with the focus being on understanding the relationship between the MIR/MAR reallocation issue (and the consequent 1.8 Hz oscillation) and the CARM loop gain. The underlying idea was that the CARM loop was marginal at the higher end of its phase bubble, and even the small change in gain induced by the change in the reallocation strategy between the HighPower and the LowNoise configurations could induce the crossing of CARM in the instability region.
The first test we did was in the (currently) standard configuration during science mode, with the splitting filters misbalanced towards the MIR correction:
The test is reported in Figure 1, where the four traces are respectively the purple, red, black and blue ones: the structures around 1.8 Hz, already present in the standard configuration, got progressively worse with the gain increased, and completely disappeared with the low gain.
We did then a test to restore the MIR/MAR reallocation filters in the low-gain condition, but this still caused the oscillation to rise and kill the lock (Figure 2).
At this point, remembering that the current CARM gain is much higher (factor ~2) than the old one, and this was mainly due to issues in the CARM loop engagement (which happens with a different filter at the end of LOCKING_CARM_NULL_1F), we wanted to test the old configuration for the lock acquisition:
Indeed the test was successful, and we left this configuration.
Then we did some noise injections on CARM, to understand better the limits with respect to B1 saturations; we used the standars LSC_noise_MICHband filter, with different amplitudes (Figure 3):
We need to understand how to reduce such glitchyness without losing effectiveness in the noise injection, which is not that great to begin with; the shape of the filter is already at high frequency, relatively speaking, and moving it towards lower frequencies is tricky; also, much of the B1_DC r.m.s. is gained at 5.2 Hz (DIFFp_TY line) and at low frequency in general. Given the saturation level being around +-0.06, we are never away more than a factor of 2-3.
The other topic of today was confined in the very last part of the shift, given the importance of the first one; we just made manually a noise injection on BS_TY OpLev in order to verify the shape of the filter and the overall noise: the shape looks fine, and a noise injection of 10x the sensing noise level had no visible effect (18:55:30 UTC, 300 s, Figure4, in purple noise is generated but not injected).
More analysis on both topics may follow.
ITF found in SCIENCE.
At 16:00 UTC, P. Ruggi and D. Bersanetti performed commissioning work on the CARM loop to reduce the oscillation at 1.8 Hz. Their work continued until 19:05 UTC. From 19:07 to 19:20 UTC, a scheduled calibration took place, CALIBRATED_DF_DAILY. At 19:20 UTC, the ITF was back in science mode.
ITF found in Science mode.
At 8:44 UTC the DMS started to report a red flag for WI_CO2_Laser - TCS_WI_CO2_PWROUT (see entry 64156).
I contacted the TCS on-call and from remote she adjusted the WI chiller set point, then at 9:17 UTC, we set Adjusting mode and she restored the standar power; ITF back in Science mode at 9:20 UTC.
ITF still in Science at the end of the shift.
ENV
Sea and windactivity increasing.
Software
At 12:50 UTC the VPM instance became frozen; it was restarted at 12:52 UTC.
Around 08.50 UTC Francesco called me from CR, because the DMS flag of WI_CO2_Laser became red for mean_TCS_WI_CO2_PWROUT value falling down.
First of all, I recovered the WI DAS outer ring power injected inside the interferometer, rotating the corresponding waveplate (action ended around 08.57 UTC)
Then, I try to recover WI CO2 main laser state by acting on its chiller setpoint:
at 09.00 UTC WI e BCK chiller setpoint changed from 19.03°C to 19.02°C → wrong direction
09.05 UTC WI e BCK chiller setpoint changed from 19.02°C to 19.04°C
Once the situation was re-established, I also recovered the waveplate (action ended at 09.20 UTC).
In Fig. 1 the main signals are reported.
I found ITF in SCIENCE MODE.
It remained locked for the whole shift except for one unlock, at 21:22 UTC, done by mistake.
Guard Tour (UTC):
21:06 - 21:36
23:05 - 23:35
01:00 - 01:30
03:02 - 03:32
I found ITF in SCIENCE. 15:32 UTC ITF in CALIBRATION to perform the scheduled activity.
17:30 UTC CALIBRATION ended, back to SCIENCE
ITF found in relocking; it relocked at 5:35 UTC and it remained in Science mode for the rest of the shift.
Guard tours (time in UTC)
From 6:00 to 6:30; from 8:00 to 8:30; from 10:00 to 10:30; from 12:00 to 12:30.
The earthwquake produced an increase of the seismic component at 1 Hz, which is a problem since the MAR/MIR actuation splitting filters have been changed: the unlock occurred when NE MIR CORR saturated (fig 1). Usually the reason of unlock during an earthquake is the saturation of MAR correction, due to the low frequency component of the surface seismic waves. A magnitude 4 in Croatia is not strong enough to produce a large slow oscillation of the suspension able to push the MAR corrections close to 10 V (fig 2). This kind of unlock would be likely avoided finding a way to restore the old MAR/MIR allocation strategy.
The earthquake is the following: M 4.4 - 4 km W of Rakovica, Croatia.
The unlock at 3:41 UTC could have been due to an earthquake. There was a seismic disturbance in both NEB and WEB at about that time.
ITF found in LOW_NOISE_3_SQZ and in Science Mode. The ITF unlocked at 3:41 UTC, and failed the relock twice at LOCKING_CARM_NULL_3F (3:57 UTC) and ACQUIRE_LOW_NOISE_1 (4:34 UTC).
Relock in progress.
No DMS alerts received during the shift.
Guard Tour (UTC):
21:06 - 21:33
23:00 - 23:30
21:34 - 22:03
03:45 - 04:17
The unlock at 3:41 UTC could have been due to an earthquake. There was a seismic disturbance in both NEB and WEB at about that time.
The earthquake is the following: M 4.4 - 4 km W of Rakovica, Croatia.
The earthwquake produced an increase of the seismic component at 1 Hz, which is a problem since the MAR/MIR actuation splitting filters have been changed: the unlock occurred when NE MIR CORR saturated (fig 1). Usually the reason of unlock during an earthquake is the saturation of MAR correction, due to the low frequency component of the surface seismic waves. A magnitude 4 in Croatia is not strong enough to produce a large slow oscillation of the suspension able to push the MAR corrections close to 10 V (fig 2). This kind of unlock would be likely avoided finding a way to restore the old MAR/MIR allocation strategy.
We started at 14:00 UTC and to not interfere with the ITF and risk to unlock, we manually injected the SQZ.
System initial status: ITF LOW NOISE 3; SQZ_MAIN @SQZ_Locked_NO_FC
14:28:26 AA loop engaged
We performed a first CC phase scan (Fig. 1-2):
14:39 CC scan started DCP = 195 Hz
15:02:21 CC scan ended (fast shutter closed), ITF in shot
15:26:15 fast shutter opened
15:36:22 ITF in SQZ phi0 = 0.65 rad
15:39:19 SQB1 TX angle set to 300 (initially at 310)
16:42:58 SQB1 X position set to -3200 (original position)
16:47:58 ITF in SQZ
After the first CC scan we realized the magnitude was similar to the last shift (entry #64094) even though there should be a higher level of injected SQZ. We decided to try to improve the magnitude by acting on SQB1_TX and SQB1_X DOFs. We worked on this from 15:39:19 to 16:42:58 UTC. Finally we left SQB1_X as it was and we changed the set point of SQB1_TX from 310 to 330 urad. The fluctuations on the magnitude are reduced (Fig. 3).
We then performed another phase scan (Fig. 4-5)
17:05 CC scan started DCP = 195 Hz
17:28 CC scan ended (fast shutter closed), ITF in shot
After the second CC scan we realized the SQZ angle is actually around 1.05 rad, so we decided to repeat the SQZ mode acquisition.
17:39:53 fast shutter opened, ITF in SQZ phi0 = 1.05 rad
17:49:08 CC loop engaged, gain=75000 (glitch between 17:54:50 and 17:56:14)
17:58:54 ITF in ASQZ phi0 = 2.75 rad
We were able to get another CC phase scan with DCP setpoint at 225 Hz (Fig. 6-7). Fig. 8 reports also the shot SQZ and ASQZ acquisitions made after the scan.
18:11 DCP value set to 225 Hz
18:44:11 ITF in shot
18:46: CC scan started DCP = 225 Hz
19:09 CC scan ended
19:15:07 ITF in ASQZ phi0 = 2.7 rad
19:22:48 ITF in SQZ phi0 = 0.95 rad
19:28 DCP value set back to 195 Hz
List of activities and actions performed during the shift:
Guard Tour (UTC)
17:08 - 17:37
19:06 - 19:32
Vacuum
16:15UTC lost of signals from 600W Tube Station
I notified A. Pasqualetti who agreed to carried out checks probably not before next maintenance.
In according with him I shelved related flags until Thursday
Figure 1. The CARM noise injection caused SR to move by ~0.5urad, because it made the B1 photodiodes saturate. It needs to be understood how the CARM noise injection shape needs to be changed so it doesn't cause B1 saturations which will spoil the measurement.
Figure 2. Normal daily hrec calibration measurements (between 16:00 UTC and 16:10 UTC) are no longer kicking the SR alignment.
ITF is found in SCIENCE.
At 6:01 UTC I set the ITF in Maintenance Mode, here is the list of the activities communicated to the Control Room:
Periodic Tasks carried out by the Operator:
| CH (W) | Inner DAS (W) | Outer DAS (W) | |
| W Pickoff | 0.255 | 0 | 0.22 |
| N Pickoff | 0.68 | 0.065 | 0.602 |
11:25 UTC Maintenance ended, I re-aligned the CITF and relocked the ITF at the first attempt, back in SCIENCE at 11:35 UTC.
11:58 UTC Vpm restarted
SQZ not working properly, F. Sorrentino contacted H. Valbruch for it.
Sub-system reportsISC
I changed the set-points of NI and WI etalon suggested by M. Mantovani.
12:13 UTC WI new set point 19.825 and NI new set point 20.1
[entry unexpectedly stuck in drafts]
During the night the WI CO2 laser changed the state, but ITF remained locked: Magazzu sent an email and report about the DMS flag in the Virgo logbook (64134).
During this morning maintenance activities were foreseen, so I waited at least for the taking of thermal camera images and chiller refilling before making actions for WI CO2 laser power recovery. After the chiller refilling and filter change, the WI CO2 main laser state was mainly recovered (see Fig. 1).
A further activity was foreseen during maintenance in TCS room (repair WI etalon heating belt, 64114). I waited for the end of this activity to further check CO2 powers (Gianmatteo already checked them 64135) and eventually act on waveplates.
At 09.00 UTC, with ITF in down, I checked all CO2 powers restoring the nominal ones. This activity has been completed at 09.18 UTC.
