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AdV-TCS (TCS studies actuation (simulations + experiments))

aiello, casanueva, fafone, mantovani, nardecchia, rocchi - 0:03 Tuesday 14 August 2018 (42425)

CO2 TCS test

After the PR alignment tuning (42423) the reaction of the ITF to the TCS actuation has greatly changed.

In fact in the morning three TCS steps had been tried with the same power on WI and NI DAS (Pin/out~[100-200]mW; Pin/out~[200-400]mW; Pin/out~[400-800]mW) and no effect was observed.

In the afternoon, we started to actuate with the TCS after 2 hours lock and we obtained an increase in the sideband gain by applying a power of Pin/out~[250-600]mW on the WI DAS

and Pin/out~ [240-580]mW on the NI DAS (see figure 1).

Two more steps have been done:

-Pin/out WI not changed, Pin/out NI increased by about 10% àno evident effect observed

-Pin/out WI not changed, Pin NI increased by about 10% more. After 5 min the ITF unlocked.

The ITF automatically relocked with TCS ON in about 10 minutes.

The trend is closer to that observed in November 2017. In figure 2 the behavior of the some more useful channels is also shown.

We also noticed a big change in the shape of B1s2 camera images (see figs.3-4).

Further investigation and tuning will be done in the next days.

Images attached to this report

Comments to this report:

fafone, rocchi - 0:09 Tuesday 14 August 2018 (42426)

We leave the ITF locked in Low Noise 1 with the TCS ON as in the last step.

mwas - 12:28 Tuesday 14 August 2018 (42432)

The change in the B1s2 camera image is most likely not relevant. This is the image of the transmission of OMC1 and OMC1 was not locked, so it is just some light leaking on the side of a frigne.

Figure 1 shows that there was a slow power drift on the camera before the step in TCS. This corresponds to the OMC slowly moving away from order ~11 mode (figure 2) and starting around 20:00 UTC starting to get close to the TEM00 mode which is the next mode in the OMC length.

However there is a bump between 20:10 UTC and 20:30 UTC, which most likely is due to the TCS, and seem to correspond to the dip in the average B1p DC power on the same time scale.

Images attached to this comment

aiello, fafone, nardecchia, rocchi - 0:45 Friday 17 August 2018 (42463)

We noticed that the 2 photodiodes on B4, PD1 and PD2, show a different behavior when the TCS is turned on (see figure 1).

At the DAS thermal lensing steady state the 112MHz measured by PD1 is higher with respect to the value with DAS off, while PD2 measures the same value when no DAS applied. PD1 is the photodiode that we usually consider to evaluate the gain.

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