[Tanaka, Ushiba, Komori]
Abstract:
We successfully mitigated the coupling issue by using the independent power supply to drive two whitening boards for the PDA1, PDA2, and PDA3.
Detail:
As a continuation of yesterday’s work (klog:36538), we compared the ALS DARM spectrum during IFO flashing under the following configurations.
The results are shown in the attached figure.
-
Turning on PDA1 (brown):
One of the PDA1 RF outputs was whitened using a whitening board that was already driven by the independent power supply.
The spectrum became slightly noisy above 100 Hz, but it did not become noisy in the 10–100 Hz band, as expected. -
Using the conventional cable for PDA3 (magenta):
The spectrum became noisy above 100 Hz, similar to the case with PDA1 turned on, but it did not become noisy in the 10–100 Hz band.
Finally, we measured the spectrum with PDA1, PDA2, and PDA3 all turned on, with the two whitening boards for these PDs powered by the independent power supply (red).
The noise level is close to the noisy reference (black) above 100 Hz, but it remains clearly lower than the reference in the 10–100 Hz band.
In other words, the total RMS is still smaller.
In fact, the DARM, MICH, and PRCL signals appeared to become quieter during arm flashing with the PRMI locked.
Please note that we confirmed that the current drawn from the independent power supply approximately doubled (~1.4 A for +18 V and ~0.8 A for −18 V) after connecting the two boards.
Correspondingly, the current meter in the computer room showed a reduction of more than 1 A.
In addition, after these modifications, we found that the dark offsets for PRCL and MICH had changed, likely due to the change in the power supply.
Therefore, we performed a dark offset compensation.
Tomorrow, we will check the stability after opening the shutter in front of the REFL QPDs.
If the IFO is not stable, we will power one of the QPD whitening boards with the independent power supply and check the stability again.
Moreover, we found that the REFL HWP before PDA1 and PDA2 was not functioning, so we will restore it.
