Virgo Logbook

AdV-COM (AdV commissioning (1st part) )

fiori, bersanetti, cirone - 17:40 Saturday 01 July 2017 (38369)

magnetic injections CEB

The interferometer being locked in acceptable conditions (Hrec_range_BNS around 6.5Mpc, Fmoder not yet optimal but slowly improving) at 17:10 LT we launched the script that performs magnetic injections in CEB. The coil setup is the one described in 37710 with the exception that the coil axis is now pointing upwards.

The script will inject 21 lines equally spaced btw 14.67Hz and 285.47Hz and the start over again for a total of 5 times. It is expected to end on Sunday morning around 7:50 LT.

Figure 1 shows a shot of the injected line at 68Hz, it is well visible in DARM.

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/data/procdata/detchar/env/Alessio/Misure_Virgo/Mag_Injections/Scripts>MagInj_sweep.py

DAC channel (i.e. NOISE_CEB_DAQroom, EEroom, DetEER, NOISE_WEB,NEB): NOISE_CEB_DAQroom
Log file name (to be read by Matlab code): MagInj_CEB_V_2017_07_01.log
Start frequency (Hz): 14.67
Stop frequency (Hz): 285.47
Number of points (integer): 21
Duration time below 100 Hz (seconds): 300
Duration time above 100 Hz (seconds): 600
Please enter measurement amplitude envelope in freq/amp pairs (a single amplitude is accepted)
For example (3 envelope points): 1 5e-1 10 5e-2 100 2e-2
Measurement amplitude envelope in freq/amp pairs: 0.5
Please enter the total number of cycles
Number of cycles: 5

Images attached to this report

Comments to this report:

fiori - 17:21 Monday 03 July 2017 (38393)

here attached is the log file with the gps of magnetic injections at CEB last Saturday night

Non-image files attached to this comment

maginjcebv20170701.txt

cirone - 16:42 Tuesday 18 July 2017 (38670)

I calculated the projection of the ambient magnetic contribution to Hrec, following the magnetic noise injections performed at CEB on July 1. In the first plot I show the coherence between Hrec and the 3 magnetometers channels, in corrispondence of the injected lines. Some of them don't produce enough signal in Hrec, so the projection is calculated only at the frequencies in which the coherence has a value higher than 0.5, in order to assess reliability. The projection is shown in the second plot for the 3 magnetometers, superposed to a nominal quiet time Hrec (slightly before the beginning of the injections). The projection was calculated by doing the product of the transfer function (between Hrec and mag) and the ambient magnetic spectrum seen by magnetometers at the same quiet time.

From this preliminary analysis it seems that the magnetic noise level is particularly high and near the sensitivity curve. In order to confirm it, We have to perform other injection studies and assess the reliability of the data processing technique. During last weeks We have done the same injections at NEB and WEB but the coherence was not high enough to perform a reliable projection. Now that we have improved the ITF sensitivity, it could be usefull to repeat injections at least at one of the end buildings. Efforts to understand this magnetic noise budget are on the agenda of these days.

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fiori - 8:08 Sunday 23 July 2017 (38775)

This comment concerns the magnetic injections done in CEB on July 1st, with the boby ("bobinone") coil pointing upwards. The projection indicates a large coupling in Hrec of the W oriented magnetic field, while N and Vertical oriented fields look quite uncoupled.

As a check I had a look at some of the July 1st injection data, in particular at 41Hz, 69Hz and 136Hz. Plots are shown in Figures 1, 2 and 3 respectively.

It can be noticed that for all of them the signal sensed by the W magnetometer was a factor of 10 lower than that sensed by the N and V(ertical) magnetometers. Consequently the TF to Hrec of this magnetometer turns out to be 10 times larger, and the projection rises.

Now, the fact that that particular magnetometer sensed a field that is 10 time less than the nearby ones is suspicious, also give the fact that in the injection done last night (boby axis pointing N) the three magnetometers sensed similar amplitudes. My suspect (to be discussed) is that the magnetometer suffered by some "shielding effect" due to its peculiar location and the peculiar configuration of field lines when the coil is vertically oriented. The three magnetometers are located inside the "L room", the W magnetometer lays very close to the concrete (iron beams embedded) wall (picture in Figure 4). This location was chosen because it is close to the old Virgo location which was just outside the L room and which now is a bit too crowded.

If we get convinced this is an issue, we will have to reconsider the location of CEB magnetometers.

Figure 5 shows a plan view of CEB with indicated the boby location (on the top terrace).

Finally, as a check of projections, we have to compute a long averaged coherence of Hrec with magnetometers.

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Paoletti - 11:16 Tuesday 25 July 2017 (38813)

Today at 10:40 Localt Time I've moved the CEB West magnetometer of about 2 meters (see photos for before-after); worth noticing that their position is not optimal, because they're surrounded by a big metallic structure.
It's now useful repeating at least one magnetic injection, to see if the low coupling with the West magnetometer changed.

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