Similar noise also appeared in April 2017, see logbook entry 37121
Also then evidence was pointing towards the splitter cooling machine in the EER room.
This splitter was installed earlier that year (Jan 2017)
Follow-up investigation:
At roughly 16:00 UTC in 21/01 the similar temperature regime as before was reached. (Fig 1) However this was not always the typical temperature behaviour of the room, but only from rhougly 30/12/2019.
At this point we see the 86Hz line after the switch on and off in ENV_EER_MAG_1 (on top of the splitter), not in ENV_EER_MAG_2. The signal in ENV_EER_MAG_1 matches nicely with the temperature changes and the observed signal in ENV_CEB_MAG_N. (Fig 2-3) However the latter is in a noisier environment and is (almost) blind to the signal.
We already knew there was a mirror image at 14 Hz. In the earlier (2017) report of the similar noise it was mentioned it went all the way up to 400 Hz. It was controlled and it wee see it indeed at 114Hz and 186Hz as well. Higher frequencies were not checked.
Why we did not see anything when we forced the switch on of the splitter yesterday is unclear.
The magnetic noise in ENV_EER_MAG_1 is roughly two orders of magnitude larger than in ENV_CEB_MAG_N, which is on its turn one order of magnitude larger than in ENV_EXT_MAG_N.
As a final remark: we see nicely that at the start of the signal it increase rapdily to 86 Hz (or decreases to 14Hz) over a distance of about 18-19Hz. (Fig 4)
Today we moved the probe ENV_EER_MAG_2 between 9:10 and 9:25 UTC times.
It is no longer on the fan coolers, but on the external part of the splitter of the EER room.
See pictures for the current set-up. The location is between the MCB-tunnel and the west arm tunnel.
Source located
Only 40 minutes after moving ENV_EER_MAG_2, the splitter turned on and we were able to see a clear signal in both ENV_EER_MAG_1 and ENV_EER_MAG_2. In the latter the signal is larger by roughly two orders of magnitude. (See figure)
We determine the source to be the outside part of the splitter.
Furthermore we notice that here we see the noise all the way upto 5 kHz, which is the full available data which is being read-out by the data-acquisition.
Now further investigation is needed to determine:
- The path of coupling: how the magnetic noise from the external part of the splitter couples to both the CEB and EXT magnetometers.
- The reason of the noise: why this specific machine produces the noise. Do others produce similar noise or not?
ENV_EER_MAG_2 is now moved from on top of the splitter of the EER room to on top of the external part of the splitter of the Injection electronic room. 7.52 UTC. This is directly below the splitter of the EER room.
Goal: make comparence between the two machines.
Important note: we noticed the probe was moved during its observation. Initially it was on the rigth-end of the machine this morning it was at the left end. This means the data might show differences due to change in location.
Therefor we taped the probe onto its current position. 7.59-8.07 UTC
Due to the bad weather forecast, I have removed the external magnetic probe at 13:20 - 13:25 UTC, leaving it just after the door, below the MC pipe.
ENV_EER_MAG_2 was moved on Monday 27/01 between 16.02 UTC and 16.09 UTC. I moved it from below the MC tube to on top of the MC tube to be closer to the tube and have a look at possible magnetic noise carried by the tube from the MSB to the CEB. Also added a figure containing the RMS of the probe and one of the current chanels of the MCB. There is clearly so comherence. Further investigation will follow.
ENV_EER_MAG_1 was removed on Tuesday 28/01 at 09.07 UTC. This descision was made since we have sufficient evidence of the splitter in the EER room and the outside part being the source of the noise being investigated. The channel has been deactivated from colleting data.