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Environmental Monitoring (Environmental Monitoring)
pierini, attadio, fiori - 18:14 Tuesday 06 February 2024 (63189) Print this report
Investigation of 401 Hz peak

Aiming to identify the turbo pump which is causing the 401 Hz peak in the hrec sensitivity, today we installed 3 accelerometers on the body of 3 different turbo pumps in CEB:

  • ENV_IB_TURBO_ACC  at IB (SIB1) turbo pump
  • ENV_DT_TURBO_ACC at DT (SDB1) turbo pump
  • ENV_SR_TURBO_ACC at SR turbo pump
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pierini, fiori, paoletti, tringali - 19:07 Monday 12 February 2024 (63245) Print this report

Following the installation of the three accelerometers, we have checked  their coherence with Hrec with respect to the corresponding sensors already present on DT, SR and IB towers. As can be seen in Figure 1, only the accelerometers on the DT (both on the turbo pump and the tower itself) show coherence at 401 Hz.

By checking the magnetometers in CEB (see  Figure 2 and Figure 3), also in this case the only coherence in from the DT magnetometer, with the only exception of ENV_CEB_MAG which is placed near to the detection lab. Please remember that all towers have their own turbo vacuum pump, each one of them rotating at a frequency near 401 Hz but with a different random drift. 

From a cross-check between Hrec, accelerometer and magnetometer (Figure 4) it is evident that those channels see the same signal. Another clue comes from the comparison of the time-frequency drift of the line in the channels (Figure 5).

As a final confirmation, we can thin about slightly changing the frequency of the turbo pump on DT while in LOW_NOISE_X and checking if the line in Hrec moves accordingly.

An open point is if the 401 Hz line enters Hrec through vibrational or magnetic coupling, and through which mechanism.

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Tringali, Fiori - 12:45 Friday 16 February 2024 (63293) Print this report

From a rough calculation of the coupling noise associated with the peak at ~401Hz:

\begin{align} h_{noise} = \frac{1}{L} \cdot CF\cdot ASD_{mag} \notag &\sim \frac{ 2.5 \cdot 10^{-9} \hspace{0.1cm}(m/T) \hspace{0.1cm} 3 \cdot 10^{-10}\hspace{0.1cm} (T/\sqrt{Hz}) }{3\cdot10^{3} \hspace{0.1cm} m} \sim 2.5\cdot 10^{-22}/\sqrt{Hz} \notag \end{align}

where L is the arm length, CF is the coupling function value measured during the near-field magnetic sweep injection (#63039) with the small coil on the DET platform (south side) Figure 1-2, ASD is the amplitude spectral density of the magnetometer ENV_DT_MAG_* which is installed on the DET tower base (East side). This value is compatible with the strain spectral amplitude (\sim1.08 \cdot10^{-22}), Figure 3.


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fiori, derosa - 11:05 Tuesday 27 February 2024 (63415) Print this report

Around 9:30 UTC we moved the ENV_DT_TURBO_MAG magnetometer closer to the DT turbo pump body, as illustrated in the attached picture. The read axis is X (radial direction).

Previous locations are described in

Figure 1 shows a spectrum at 401 Hz of this sensor compared to the magnetometer on the DT tower base. The sensor on the pump body measures a quite intense 401 Hz line (approx 500 nT/sqrtHz). Yet, it does not see the sideband structures which are seen by the DT magnetometer and which were sensed close to the turbo cable.

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