J. Driggers, S. Dwyer, J. Kissel, T. Sadecki

We were able to successfully move the spot position on ITMY this afternoon, while in otherwise Nominal Low Noise at 37W, in order to make progress toward reverting the global alignment position to prior to the position found to work on July 30 / 31, as part of the plan to fix several problems that have arisen because of the new position (see LHO aLOG 51262). 

Progress was stalled then halted due to a GW event candidate (yay!), and 30 minutes later a lockloss from an earthquake in Mexico (boo!).

Here's a mid-adventure report so there's less to talk about later.

The path for the spot position move was to swing *around* the point absorber. As such, Jenne and Sheila did the following:
    - Increased the gains on the ADS YAW 3 loop (from 1.0 to 10.0) and the SRC1 PIT / YAW loops (from 12 to 18, and from 4 to 6, respectively)
    - slowly adjusted the A2L gains on ITMY (H1:SUS-ITMY_L2_DRIVEALIGN_P2L_SPOT_GAIN and H1:SUS-ITMY_L2_DRIVEALIGN_Y2L_SPOT_GAIN) 
        - first swinging "out wide" in YAW, increasing the gain from 0.0 to 3.5
        - then restoring the PIT position / gain to the Prior-to-July values (from -2.0 to -3.0)
        - then restoring the YAW position / gain from 3.5 to 0.0
        - then changing the ITMX PIT and YAW positions to minimize the coupling to DARM (the ITMX position and ITMY position are closely coupled by the ASC system, but we don't use the ADS system to servo the spot position on ITMX to the same place.)
Notably, we were discussing a path forward when the GW candidate came through, so we had not yet moved the spot positions on the ETMs before we lost lock.

We noticed several things along our journey and about our end positions -- to see these conclusions, check out the trends of relevant channels during the spot moves today (2019-08-14_DuringSpotMove_After.png), and just before we moved them on July 31 (2019-07-31_DuringSpotMove_Before.png):
    (1) [Row 0, Column 2] RF45 Noise has returned to July-level noise -- drastically reduced. Great! (as displayed by H1:LSC-REFL_A_RF45_DEMOD_RFMON) 
    (2) [Row 0, Column 0] The POP18 build up is actually a bit *higher* than July-level. Great! (as displayed by H1:LSC-POPAIR_B_RF18_I_NORM_MON)
    (3) [Row 1, Column 3] The DARM coupled cavity appears to be a bit higher than the July-level. Great! (as displayed by H1:CAL-CS_TDEP_CAVITY_POLE_RAW_F_C_MON / 400 Hz) 
    (4) [Row 0, Column 0] PRC gain is roughly the same. Good. (as displayed by H1:LSC-PR_GAIN_OUT16)
    (5) [Row 1, Column 3] The DARM loop optical gain (\kappa_C) is a bit lower,  but we haven't tuned up the OMC ASC alignment offsets yet. OK. (as displayed by H1:CAL-CS_TDEP_CAVITY_POLE_KAPPA_C_MON)

Also note that a before vs. after spot position move drastically cools the HWS image around the point absorber -- consistent with the fact that the new positions no longer heat up the point absorber (see 2019-08-14_H1HWSData_FromReferenceToHoldPoint_2.png).

These effects lead us to believe that we're doing the right thing by going back toward the pre-July spot positions. Indeed, we are even considering *not* moving the ETM spot positions, because the cavity pole and DRMI power / POP18 buildups are a bit better than before. Jenne remind us that the ETM spot positions were chosen *solely* because they were the former positions that had the highest buildups back in the late Apr / May, so we're not married to them.


However, since all this was half-way through our goals for the day, we now have the following ideas/plans forward if we relock quickly:
    (a) Re-lock the IFO without doing any initial alignment -- hoping that our work will not have gotten lost with the EQ.
    (b) Re-acquire all the way to DC readout at 2W (i.e. after full IFO alignment, and SOFT LOOPS have been engaged).
    (c) Gather/Record initial alignment references at both centered spot positions (all zero A2L gains) as well as either today's new positions (IY and IX restored, but with ETMs still at Early Aug values) or Pre-July positions. 
        >> decision point at this time unknown -- to which do we set the initial alignment offsets -- centered, Pre-July, or New?
    (d) Head up to full 37W.
    (e) Tune up OMC ASC alignment loop offsets to regain as much DARM loop optical gain as possible
    (f) Remeasure sensing function.

We'll see how far we get. We're still formulating a plan for "what if we don't get even past (b)" for the operator corp to do overnight.

For future reference, I also attach a more detailed but more rough diary of the afternoon's activity (2019-08-14_SpotMove_Diary.txt).
I also attach a screenshot of the spot positions I reference in this aLOG: Pre-July 30/31, Post July 31, and Today. (2019-08-14_H1TM_SpotPositions.png)