• 9:25 OMC DCPD alarms begin
• 9:59 Went out of Observation Mode (since I saw LLO was out...they were running A2L to help L1)
  • At this point I was on phone with Kiwamu.  We determined we had a violin mode rung up, and ultimately found it to be ETMy's 2nd order mode (1008.45Hz).  We referenced Dan/Nutsinee/Evan's 2nd Order Violin Mode Table Alog 20345.
  • Started to address this.
  • When first alarms occurred, the range was fine, but as the violin mode rung up more, the range began to nosedive (from 80Mpc eventually down to 30Mpc).
  • We found that for ETMy, MODE3 was obviously noisy with HUGE outputs
• Started to look at ETMy.  Changed gain to try and bring down violin mode (gain started at 100, I took to 50 and saw no effect.  I went to -100, and H1 broke lock.).  While doing this, Kiwamu said he was going to come in.
• 10:41 Lockloss

Note:  at the beginning I trended a channel which was red in the ODC Overview (H1:0MC-DCPD_A_INMON) & over the last day, these dcpds have been noticeably getting big during the last two locks (starting at 10/24 11:00 utc).  See attached plot for these PDs getting rung up (presumeably due to the ETMy violin).