jeffrey.kissel@LIGO.ORG - posted 17:08, Tuesday 30 July 2019 - last comment - 19:26, Tuesday 30 July 2019(50935)
Maintenance Day Recovery: ITMY Camera Bumped, ITMY Alignment Reference Lost
J. Jones, J. Kissel, K. Kawabe, N. Lecoeuche, R. McCarthy, D. Sigg, T. Shaffer, J. Warner IIET Ticket 11931 It was identified rather early that during a tune-up of ITMY's red camera, the known-to-be-problematic (see above referenced IIET) ITM Green Camera housing got bumped (LHO aLOG 50915). A blow-by-blow of the recovery is attached, but in summary, we - bypassed the ALS ITMY green camera loop during initial alignment (because we knew the ITM hadn't moved since the last nominal low noise segment), - had three patterns of lock losses, but got far enough in the acquisition sequence (ENGAGE_ASC_FOR_FULL_IFO) to *roughly* measure the new reported correct position on the ITMY green camera, - adjusted the ALSY camera offsets to be close to the right position, - re-ran initial alignment, and - slightly adjusted the ITM further to get past the CARM reduction. All in all, we changed the camera offsets by ~30 cts in pitch, and ~100 cts in yaw, and we needed to move the ITM -0.4 urad in yaw to get past the COMM to TR_CARM hand-off. We started attempting recovery at around 11:00a local (~18:00 UTC), and hit nominal low-noise at ~4:00p local (23:02 UTC). We have now lost lock again (for an unknown reason), and are testing out the robustness of the acquisition sequence with the new ITM position. Note, that, if successful again, we're going to adjust the ITM camera offsets *again* to better match the additional move. More details to come.
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The three patterns of lock losses today: (1) ALS X green WFS DOF1 pulls the X-ARM off in to the weeds after LOCKING_ARMS_GREEN, killing the green lock. This is unrelated to he camera bump, and a common, regular annoyance. The work around, is to turn OFF the input to ALSX WFS DOF1 for a bit, until the other DOFS converge, then turn it back on again. (2) At CARM_TO_TR, when the IFO REFL (not IMC REFL) Common Mode Board's inputs from the summing node are being transitioned from COMM to the normalized TR signals. We attribute this to poor co-alignment of green to red, as a result of initial alignment to a poor green reference. I've since adjusted the ITMY position in -0.4 urads in YAW on the slider (from -165.9 to -165.5 urad; where -165.9 was the position during the last NLN segment, which hadn't benn moved or adjusted during maintenance) (3) During ENGAGE_SOFT_LOOPS, as the ADS system tries to yank ITMY in the right position for nominal low noise. Only (1) and (3) are sill occuring. And in his new ITMY position, (to which we have not yet adjusted the green camera offset, nor have we re-run an initial alignment), the POP18 build-ups are lower than normal (usually 65-70 counts, and now is repeatably 55-60 counts). So, we're going to continue to work around (1) by turning OFF ALS X DOF1 PIT input, and we're going to continue to work on finding the right ITMY position by (a) noodling around with ITMY again with DRMI locked, and (b) if successful, adjust the camera offset further, then (c) try to get through (3) again, and if that fails, then (d) run through initial alignment with the further adjusted ITM camera offset position.
J. Kissel, P. Thomas
We have done (a) through (d) mentioned above. Now POP18 buildup has been restored to ~65 during DRMI acquisition.
PIT YAW
New ITM position: 29.9524 (might as well be 30.0) -165.251 (might as well be 165.3)
New camera references: 239.3 210.7
We're re-acquiring, and we've made it once to CARM_ON_TR (problem (1), then once to ENGAGE_SOFT_LOOPS (problem (3)).
ALS Shutters were open (we skipped SHUTTER_ALS) in order to continue watch the ITM alignment as reported by the ITM green camera, but I don't think this is necessary from here on out.
ENGAGE SOFT LOOPS makes it as far as starting to pull the recycling gain back up, but the POP18 buildup drops in to the high 50s while that happens, which causes a fast lock loss.
I'm out of steam for the night and heading home.
I've leave Patrick with now bright ideas on how to proceed further, so feel free to call in and offer him some advice.
Otherwise, he's just going to keep trying to get through the sequence, hoping to get lucky and get past the POP18 drop like we did earlier this evening for our one 1 hour NLN stretch.