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AdV-INJ (ITF Mode Matching Telescope)
derossi, gosselin, mantovani, magazzù, spinicelli - 12:17 Thursday 30 October 2025 (68063) Print this report
ITF mode matching measurement

As a part of the global check of the status of any part of the INJ subsystem that could be related to that recent issue we performed a mode matching measurement with the kick method (i.e. applying corrections on the end mir z and analyzing the 02 mode during the free swinging). The last measurement was done in June 2024 #64450.

We had to repeat twice the procedure because in the first attempt only the north arm data were good. At the end, the gps used for the analysis are:

- 27/10/2025 18:44:24 UTC, 102 s (North arm) 

- 29/10/2025 19:10:00 UTC, 120 s (West arm)

The analysis started 25 and 40 sec after the unlocks for the North and West respectively (so that the ITF should be still "hot"), see plots 1 and 2.

We found high values for the mismatch: around 4% for the north and 5% for the west. 

We could try to improve it by tuning the mode matching telescope.

 

 

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derossi, spinicelli - 15:51 Monday 03 November 2025 (68087) Print this report

This morning we improved the mode matching by tuning the mode matchig telescope on SIB1.

The meniscus lens and the counterweight are open loop picomotors, which are kept switched off during the run. We thus went to switch them on and we found the multiplug of the picomotors broken (front of the minirack on the bottom, see pictures 1 and 2).

In total we moved L1z by 50000 steps backward and the conunterweight 400000 backward to keep the Sc_IB_MAR_TZ_CORR close to 0V.

The improvement of the matching is shown in fig 4. Here the measurement is made on the cold interferometer by making the scan of the arms with the green. From 2.4% to 1.3% on the west and from 1.8% to 1.3% on the north.

The measurement on the hot interferometer with the kick method gave 2.6% for the west and 3% for the north (starting from 5% and 4% #68063), fig 5 and 6.

The GPS of the scan are the following

 

TEM 00 TEM02   mismatch North (green scan cold) mismatch West (green scan cold)
10:15:24 UTC 10:19:41 UTC   1.7% 2.4%
10:41:38 UTC 10:45:14 UTC L1z 20000 forward (worsen) 2.2% 2.9%
11:08:08 UTC 11:11:43 UTC L1z 50000 backward 1.5% 1.7%
11:29:30 UTC 11:33:06 UTC L1z 20000 backward 1.3% 1.3%

 

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