Virgo Logbook

AdV-TCS (CO2 laser projector)

fafone, giri, nardecchia, rocchi, casanueva, valentini, ruggi - 16:48 Friday 09 April 2021 (51373)

NI CH Tuning

At the beginning of the shift, the CH settings were:

P_WI = 41 mW
P_NI = 15 mW

Identified by the pink star labelled “Start” in figure 1. Figure 1 shows the gain of the 56 MHz sideband gain for the CH powers. Thus, according to the simulation, increasing the NI power, while keeping the WI constant, will improve the gain.

Reminder: when the steady state has been reached after each step in the CH power, ISC team checked the alignment.

Steps	UTC	Power injected in ITF in WI	TCS_WI_CO2_POWER_CH_PICKOFF	Power injected in ITF in NI	TCS_NI_CO2_POWER_CH_PICKOFF
1	7:47:24	41 mW	0.251 W	21 mW	0.14 W
2	08:46	41 mW	0.251 W	29 mW	0.183 W
3	09:24	41 mW	0.251 W	36 mW	0.23 W
4	10:00	41 mW	0.251 W	42 mW	0.265 W
5	10:32:26	41 mW	0.251 W	48 mW	0.302 W
6	11:16	41 mW	0.251 W	56 mW	0.356 W
7	11:58:36	41 mW	0.251 W	65 mW	0.409 W
8	12:28:02	41 mW	0.251 W	74 mW	0.464 W
9	13:40:50	41 mW	0.251 W	56 mW	0.356 W

After step 8, we observed a decrease of the sidebands’ absolute values and hence, at 13.40:50 UTC, we came back to the value set at step 6 (see figure 2).

We left the CH in the following configuration:

P_WI = 41 mW
P_NI = 56 mW

To be sure to be sitting on the maximum of the sidebands power, the equivalent scan for the WI CH should be done.

Images attached to this report

51373_1617979682_Screenshot 2021-04-09 at 16.47.16.png

51373_1617979691_Screenshot 2021-04-09 at 16.47.33.png

Comments to this report:

Casanueva, Ruggi, Valentini - 17:22 Friday 09 April 2021 (51375)

The ISC team activity focused on supporting the Central Heating tuning activity.

The central interferometer was aligned and locked at 7.40 after tuning of the SRCL gain. The UGF monitor lines have been turned on with the following frequencies and amplitudes:

MICH LINE: Freq 31.1 Hz Amplitude : 0.02
PRCL LINE: Freq 67.1 Hz Amplitude: 2e-4
SRCL LINE: Freq 33.3 Hz Amplitude: 0.07

At the beggining of the shift, the 11.6 Hz PR vertical oscillation was excited, but an intervention was able to damp it with success (see logentry 51368)

At 7.42 UTC the TCS tuning activity started. Due to the change in the recycling gain of the sidebands during the TCS transients (See figure 1), the GAIN og the PRCL, MICH, and of the PR_TY AA loop required to be reduced several times in order to keep the loops stable. The SRCL UGF remained instead stable (except for a change at 9.16 UTC due to a realignment of the BS) and did not require any gain tuning during the NI CH transients. The gains were changed as follows :

DOF	Initial Gain	9.18 UTC	9.56 UTC	11.50 UTC	12.56 UTC
PRCL	0.2	0.167	0.146	0.124	0.124
MICH	2.5	2.5	2.5	2.0	1.43
PR_TY	0.5	0.5	0.5	0.3	0.3

Additionally, the B1p quadrants galvo loops have been enabled during the shift and the quadrant signals have been checked to be good error signals for the alignment of the BS (see figure 2)

Images attached to this comment

ruggi - 14:14 Saturday 10 April 2021 (51381)

Some additional information about the possible reconstruction of BS angular signals from B1p quadrants:

- Signals are present both on QD1 and QD2, but QD2 looks a bit better;

- the recontruction is possible using both 6MHz and 56 MHz; in fig 1 the reconstruction of BS_TY is done multiplying B1p_QD2_6MHz by 100, and B1p_QD2_56MHz by 350 (the demodulation phase is far from being optimal)

- there is also some signal for SR alignment; in fig 2 we can see a reconstruction of SR_TX obtained combining 6MHz and 56MHz --- [SR_TX=(Q6-Q56*2)*4000].

Images attached to this comment