This is a summary of the activities performed on DET yesterday (Sep 24).

1/ SDB2 recovery in vacuum:

After the vacuum was restored in the SDB2 minitower, we performed several checks described in this entry.

First, noticing that the correction in SDB2_LC_TX_corr was around 4V, we reduced it by acting on the motorized counterweight along the EW axis by - 80000 steps. We reached a correction lower than 1V.

Andrea restored the NI single bounce. SDB1 B5 beam drift control closed and OMC shutter open at 13h54 LT.

Corrected B1 PD1/2/3 DC offsets at 14h16 LT. To be noted that when I reloaded the configuration of SDB2_dbox_bench, the process SDB2_LC became blue. Stopping and restarting the process SDB2_LC (after opening the angular and position loops) solved the isssue. Next time Alain suggests to reconfigure the ADC mezzanine reading the LVDT "in" instead of stopping/restarting the process.

B1 PD1/2 alignment check:

We scan the OMC over the 56 MHz side band TEM00 and the carrier first order mode (Figure 1). The 56 MHz TEM00 does not allow to have a good error signal with B1_PD3. Instead the carrier first order mode gives about 1.8 uW on B1_PD3, which should correspond to about 8 or 9 mW on B1.

OMC locked on the first order mode at 14h45 LT. But it unlocked during the daily meeting and then the lock was not very stable. So we simply stabilized the OMC temperature on the resonance of the first order mode in order to check the alignment of the B1 photodiodes.

Checking alignment of B1_PD2 by acting on B1_M2 H picomotor : power plateau ends at +10000 steps. Opposite edge of the plateau at -3000 steps. Finally we performed +3500 steps in TY (with respect to the initial position) to be in the middle of the plateau.

Checking alignment of B1_PD2 by acting on B1_M2 V : plateau ends at +5000 steps. Opposite edge at -12000. We performed -3500 steps in TX (with respect to the initial position) to be in the middle of the plateau.

Checking alignment of B1_PD1 by acting on B1_M3 H : plateau ends at +18000. opposite edge at -10000. We performed +4000 steps in TY (with respect to the initial position) to be in the middle of the plateau.

Checking alignment of B1_PD1 by acting on B1_M3 V : plateau ends at +13000. opposite edge at -8000. We performed +2500 steps in TX (with respect to the initial position) to be in the middle of the plateau.

B5 alignment check:

Nominal angular position of SDB2 TY is +880 urad. scan bench position in TY (see Figure 2). We can see that the position TY=880 urad is very close to the middle of the plateau so we do not need to realign the B5 photodiodes.

Measurement of B1/B1_PD3 ratio:

We correct again the offset on B1_PD3. SDB2_dbox_bench reloaded at 14h30m06 utc (this time the process SBD2_LC was not impacted by the reload of SDB2_dbox_bench). After this offset correction we measure the ratio between B1_DC and B1_PD3_DC (Figure 3). The ratio is around 2500, which is about a factor 2 smaller than expected from similar measurement in January 2024 (https://logbook.virgo-gw.eu/virgo/?r=62903).

Therefore we checked the alignment of B1_PD3 by scanning the picomotors of B1_M4. We performed a little correction with -2000 steps in H and -2000 steps in V.

We correct again the offset of B1_PD3 at 14h57m08 utc. The obtained ratio is equal to about 2350 as shown on Figure 4.

Data for the blending of the B1 photodiodes:

From 14h39m34 utc to 14h53m34 utc we were only acting on the B1_M4 picomotors for the alignment of B1_PD3. Thus this data may be used for the update of the blending filters.

We also take "quiet" data (without any action) from 14h59 utc to 15h07 utc with the OMC still close to the resonance of the first order mode.

Other information:

At 15h13 utc we checked  that the B1p and B5 galvo loops can be closed using DC centering confirming that we did not break any galvos.

Noticing that the corrections on the vertical degree of freedom of the SDB2 suspension were getting close to saturation, we contacted Henk Jan who restored a good working point (https://logbook.virgo-gw.eu/virgo/?r=67789).

Around 16h30 utc we stopped the pump of SDB2, the residual gaz pressure inside the minitower was 0.11 mbar.

Fig.5 shows the evolution of the temperature inside the electronic container after 1 night, as well as the evolution of the pressure and temperature inside the B1 airboxes. Everything thing seems normal so far. We are still in the temperature transient.

Replacement of B1t photodiode on the EDB bench:

Around 18h30 LT we went to the detection lab in order to replace the B1t photodiode (in transmission of the external OMC) on the EDB bench. We removed the old photodiode and its external preamplifier SN221 (https://logbook.virgo-gw.eu/virgo/?r=66711) and replaced it with one of the photodiode removed from SDB2 that is still inside the airbox 09.

Then we tried to stabilize the external OMC close the resonance of the HOM of order 4, but the power was fluctuating a lot, making it difficult to check the alignment of the B1t photodiode. As we were not able to engage the OMC lock we contacted Michal who succeeded to lock the OMC on the carrier TEM00 mode (after changing the OMC operating setpoint by -1deg to reduce the Peltier current and after increasing the gain by a factor 10). After this we centered the beam on the new B1t photodiode.

We concluded the activity in the detection lab yesterday evening and asked the operator to relock the arms for the night.