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AdV-TCS (TCS control system)
bersanetti, chiummo, derossi, nardecchia, rocchi, spinicelli - 0:03 Friday 20 May 2022 (55916) Print this report
CO2 Actuator tuning keeping the arm matching followup

The goal of this shift was to continue the work started yesterday afternoon, i.e. to compensate the north CP cold lens with the DAS power. 

Since last time we checked several values of the outer ring, this time we decided to start from the best point of yesterday (Inner ~70mW, outer ~1W) and to change only the inner power.

To be noted that, as explained after the morning shift, in order to avoid misalignment of PR/BS and arms we perform an unlock/realignment each ~20-30 minutes and we use the new function for the drift control of the arms on the green during all the scans.

A summary of all the several steps performed are shown in figure 1. It seems that the last power chosen for the inner ring (~700mW) improved a lot the north arm matching, which is now close to the west one. Also, it appears that after ~45 minutes we reached the minimum for the north matching . It is maybe worth to fine tune tomorrow morning the inner power around the last chosen value.

In agreement with Alessio, we then decided to leave the arms locked in IR with the North Inner DAS ON.

 

Below a detailed list of the actions:

We first scan the TEM0 and TEM2 with only the inner NI ring switched on at 14:06 UTC for TEM00 and 14:16 UTC for TEM02

We then put the outer DAS  at 1W: 
1337005078  19 May 2022 14:17:40 UTC  (19 May 2022 16:17:40 CEST)

and we leave the scan of TEM2 going on.

Unlock & cavity realignment
1337006416  19 May 2022 14:39:58 UTC # self unlock
1337009119  19 May 2022 15:25:01 UTC  (19 May 2022 17:25:01 CEST)

Scan of the TEM0 mode
1337009456  19 May 2022 15:30:38 UTC  (19 May 2022 17:30:38 CEST)

Unlock & cavity realignment
1337010062  19 May 2022 15:40:44 UTC  (19 May 2022 17:40:44 CEST)# self unlock

After thermalized, we do a first step on the inner ring, doubling its value from 60 to 120mW:
1337010492  19 May 2022 15:47:54 UTC  (19 May 2022 17:47:54 CEST)

and then we start back the scan on TEM02

Unlock & cavity realignment
1337012028  19 May 2022 16:13:30 UTC  (19 May 2022 18:13:30 CEST)

We do a TEM00 scan
1337013927  19 May 2022 16:45:09 UTC  (19 May 2022 18:45:09 CEST)


The matching seems to improve, thus we decide to double again the inner das up to 250mW:
1337014819  19 May 2022 17:00:01 UTC  (19 May 2022 19:00:01 CEST)

Unlock & cavity realignment
19 May 2022 17:08:30 UTC
1337015565  19 May 2022 17:12:27 UTC  (19 May 2022 19:12:27 CEST)# self unlock

At this time, we experienced a failure while doing the Fmoderr with the automation and we found out that it was due to the hardware. In fact the LNFS (low noise frequency synthesizer, for the 56, 6 and 8 MHz sidebands generation) was in a faulty state. We solved it by switching off and on again but  the data acquired till 17:30 UTC are not reliable.

Once the LNFS problem solved, we start again with a TEM00 scan 
1337018984  19 May 2022 18:09:26 UTC  (19 May 2022 20:09:26 CEST)

We start back to scan the TEM02
19 May 2022 18:17:35 UTC

Unlock & cavity realignment
1337020729  19 May 2022 18:38:31 UTC  (19 May 2022 20:38:31 CEST)

We unlock again to start the new measurement, and we do a TEM00 scan
1337021485  19 May 2022 18:51:07 UTC  (19 May 2022 20:51:07 CEST)

The matching seems to improve, we decide to double again the inner das up to 410mW
1337021506  19 May 2022 18:51:28 UTC  (19 May 2022 20:51:28 CEST)

Unlock & cavity realignment
1337024342  19 May 2022 19:38:44 UTC  (19 May 2022 21:38:44 CEST)


The matching improves very slightly, we decide to increase again the inner das up to ~710mW to see if we can find a value where the matching degrades:
1337027106  19 May 2022 20:24:48 UTC  (19 May 2022 22:24:48 CEST)

We redo the scan on TEM00
1337027210  19 May 2022 20:26:32 UTC  (19 May 2022 22:26:32 CEST)

Unlock & cavity realignment
1337028880  19 May 2022 20:54:22 UTC  (19 May 2022 22:54:22 CEST)

 

Images attached to this report
Comments to this report:
fafone, rocchi - 0:29 Friday 20 May 2022 (55917) Print this report

We have computed the focal length of the DAS lens with the current settings (0.7 W inner and 0.95 W outer) and the result is about 33 km (very close to what estimated in 55895). 

The initial value (0.1 W inner and 2.0 W outer) used yesterday (55898 and 55900) gives a focal length (27 km) off by 20%.

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