J. Kissel

One of the design considerations for A+ larger beam splitter suspension is whether to add actuation on to the final (optic) stage of suspension. The primary motivator for doing so is to improve DRMI lock acquisition speed. In order to model whether that will be useful, and/or whether the change in force allocation will affect things like whether we'll be able to constantly run broadband feedback on the second stage of the supporting isolation platform (whether we can run isolation loops on stage 2 on the BS ISI), we need some representative times in which DRMI is attempting to lock as a part of a normally functional full IFO acquisition sequence on the aLIGO beam splitter suspension, which only has actuation at the penultimate (M2) and top (M1) stages. The following are a list of times gathered today:
    Sep 27 2018 17:39:00 - 17:41:45 UTC
    Sep 27 2018 19:25:00 - 19:40:00 UTC
    Sep 27 2018 21:15:00 - 21:35:00 UTC
    Sep 27 2018 23:18:10 - 23:21:40 UTC
As per normal, the BS ISI ST2 feedback loops are off, but the platform (and HEPI) otherwise fully functional as designed 
    - ground to ISI sensor correction is on for X and Y, with CML_BB_SC (Conor Mow-Lowry Broad Band Sensor Correction filters)
    - ground to HEPI sensor correction is on for Z, with Mitt_SC (Rich Mittleman broadband Sensor Correction filters)
    - all ST1 DOFs besides Z have "Quite 250" blends, Z has 45 mHz blends. 
As for the suspension, 
    - top-mass OSEM damping is ON, 
    - optic (M3) to penultimate (M2) stage optical lever damping is ON. 
    - penultimate M2 coil drivers are in their highest range stage (state 2), 
    - top mass (M1) coil drivers are in the low-noise state (also state 2). 
    - The top mass has DC alignment offsets that are eating up only about 10% of the DAC range at the top mass (M1).
    - during lock acquisition, there is no global alignment control present, only longitudinal. However, there is some frequency dependent 

If anyone needs a refresher on more about each stage of aLIGO beam splitter's actuation strength, check out T1100602.