With the help and advice of vacuum team today we switched off some devices at WEB. We found that the the ITR gauge pressure devices were contributing to the 0.5Hz and 5Hz magnetic combs. One such device is located at the tower base level, N side (close to where magnetometers are presently located) and a second device is located at the platform first floor, East side.

Figures 1 and 2: once switched off the devices (power plug disconnected) the magnetic noise measured by the magnetometers reduced in a broadband range by up to 1 order of magnitude.The 0.5Hz magnetic comb at low frequency seems completely removed. The 5Hz comb, affecting mainly above 100Hz is greately reduced but some residual is still present.

Figure 3: we do not see a sizeable effect in Hrec. Also coherence with magnetometers and UPS probes in the region from 40 to 60Hz seems more or less unchanged.

The devices were powered on but, according to VAC team, not actively queried for data. Now both devices have been left powered OFF with the power plug disconnected.

We could not investigate, because of limited time, if the stray mag fields were radiated by the source and/or by the cables.