camilla.compton@LIGO.ORG - posted 10:07, Tuesday 18 June 2024 (78433)
Kappa TST not changing much since October 2023
Kappa TST has not been changing much since October 2023.
Question: why did Kappa_TST stop changing? Plot attached. Unsure. In O4b the new DARM reduced force used on ETMX L3 but this seemed to happen after kappa_TST stopped changing.
As described in 76326 "kappa_TST is the time-dependent correction factor that tracks the TST stage actuation strength relative to the last time the calibration was updated", but the calibration hasn't been updated more regularly, so if it was still changing, we should see it. Francisco has made a script to automatically adjust the ETMX L2L drivealign to compensate for Kappa_TST but this only started this week: 78425.
In October Ryan's anaylsis showed the Kappa TST drift agreed up with increasing charge on ETMX from in-lock charge measurements: 73613, recent in-lock charge measurements in 75456 show the charge hasn't changed much. To do: check on in-lock charge measuremtns and add a longer time scale plot.
Images attached to this report
