The audio files of this new noise are generated using the microphone located in the NE experimental hall, ENV_NEB_MIC, during the following times:

Mar 9, 12:04:20 UTC, gps=1394021078 , dur=50 sec;
Mar 9, 12:15:20 UTC, gps=1394021738 , dur=50 sec;
Mar 9, 15:53:10 UTC, gps= 1394034808, dur=50 sec;
Mar 10, 07:17:20 UTC, gps=1394090258, dur=50sec.

Today at around 4 pm, we turned off the turbo of the NE tower, suspected of producing the recorded noises (possible controller malfunction)

To be checked the unlock from CARM_NULL_1F (shutter open) occurred at 18:50 UTC

From a quick look, considering the excited frequencies and the concerned sensors, I would say it is very similar to the "mysterious" noise.

Figure 1 shows the event of 18:50 UTC (pointend out by Francesco)

Figure 2 shows the previous event (15:05 UTC) (double) which was followed right after by the action by Antonio.

The TCS door left open seems not to alter the 25m glitch rate, but some effect is visible at the CHROCC level

Answering a question that arose during today's commissioning meeting: the TCS room temperature variation (1.6 degC) obtained opening the door was performed while the ITF was having lock problems (NEB noise), so there are few glitch samples available for refined analysis.

However, looking at past data, we can see that the TCS room already had the same variations, so we can analyze the old data to find a correlation with the glitch rate at 25m.

as a followup of the investigations of the new noise at NE,  during last tuesday break - 12/03 morning - we did the following :

- restarted the main turbopump (400 Hz)
- stopped  the 'spare' pump (820 Hz) which has been in operation for months

warned by Fabio, at around 1915LT  we again switched OFF the main turbopump at NE and switched ON the spare one. Apparently the pump did not emit any alarm, anyway the sound recordings are likely from a malfunctioning turbo pump.

In practice, this is the same configuration tested in 63550 .

Note: the spare pump rotating frequency has been set at 547 Hz

"NE mysterious noise"

One additional event occurred March 16 at 22:23 UTC and caused an unlock: Figure 1 (trend), Figure 2 and Figure 3 (spectrogram of accelerometers). The frequency of the turbo pump line (547Hz) did not seem to be affected at all (Figure 4). 

At that time, according to Antonio's and Fabio's reports: the main turbo pump was switched off and the spare turbo pump was on, the accelerometer named ENV_NE_BOTTOM_ACC was placed on the main turbo (see picture in Figure 5).

Figure 6 compares the spectrum of this accelerometer (orange) with similar accelerometers on the NE big flange (blue) and on the NE cryo trap (green). The signal seen by the accelerometer on the main pump indeed  detected a large signal.

We moved the accelerometer named ENV_NE_MIDDLE_ACC on top of the spare turbo pump. See picture in Figure 7.

We switched off the external cooling fan of the main turbo.

Extra glitches in accelerometer ENV_NE_ACC_Z:  in Figure 2, we notice several fast glitches which are not seen by the other accelerometer. Need further investigation. 

I've added the "INF_TCSroom_TE" channel to the previously shown data of the glitch period. Fig. 1 shows the most correlated temperature channels with the glitch period. The channels have been time shifted according to what Francesco extracted (https://logbook.virgo-gw.eu/virgo/?r=63479).
The shif of this new channel is around 7 h before the glitch period making it even earlier than "INF_NI_BOTTOM_TE1" by almost 3 h. Although, the correlation seems smaller compared to the "BOTTOM_TE1" channel.

Fig. 2 shows a close-up of these channels.

This afternoon we switched off the controller of the main turbo at NE, suspected of somehow producing disturbances even when the pump is stopped .