elenna.capote@LIGO.ORG - posted 17:30, Wednesday 16 September 2026 - last comment - 18:24, Wednesday 16 September 2026(91943)
Power through JAC is 4-5% less than before EOM swap
We noticed this today while debugging alignment issues. I compared the powers for 10 W request from PSL.
| Now | Before Swap | |
| H1:IMC-PWR_IN_OUT16 | 10.0 W | 9.96 W |
| H1:IMC-IM4_TRANS_NSUM_OUT16 | 8.78 W | 9.17 W |
| H1:IMC-MC2_TRANS_NSUM_OUT16 | 1491 | 1559 |
| H1:JAC-TRANS_A_LF_OUT_DQ | 30650 | 32107 |
All of sensors beyond the JAC agree that there is 4-5% less power now making it to the IMC.
This issue explains why I was having alignment problems today- "SRY Locked" checks for AS A DC NSUM to be greater than 4000, and with the good alignment I have found we've reached about 3900.
I trended the AS A NSUM for SRY locking and found that with our best alignment, we should be able to achieve 5000 cts on AS_A and 0.06 W on AS_C. However, I have maximized the SRY alignment with the SRM sliders (and also ran SR2 align and AS centering), and the best I can achieve is 3900 ct and 0.047 W, which is considerably less power than the 5% reduction I reported above.
Previous SRY from last week shows what values we expect at AS for SRY
SRY attempt today shows that I have maximized the SRY alignment and achieve the buildups listed above.