While we were in commisioing mode, we had a strange non stationary spectrum, with large non stationary noise also appearing in MICH and PRCL. I quickly looked at some triple witness sensors, since we've had issues with these recently, but didn't see anything obvious.
The strange noise started a few minutes before 2:50:34 UTC Sept 10, seemed to get better for a few minutes and then got worse again around 2:57:21.
We don't think that this was related to any comissioning we were doing. Evan had temporarily lowered the DARM ugf and put a notch in, (which should cause anything like this). He undid both changes when we saw the unusual noise, but the noise was unaffected by his change.
We aren't going to investigate any further right now since the problem seems to have gone away.
This is happening again. (this time it seems worse) It started about a half hour ago, at 22:30 UTC on Sept 14th
We ran a bruco on 5 minutes of this excessively noisy period (2015-09-14 22:55:00). Results here.
From 10 Hz to 1 kHz, most of the LSC and ASC signals are coherent with DARM, so it's hard to say what's going on here.
Above 1 kHz, there is some coherence with the RFAM monitor on the EOM driver. A series of spectra are attached showing elevated RIN in this monitor, compared to a quiet period roughly 30 minutes later. What mechanism could cause this? Also included are spectra of the LSC magnetometer in the CER, since this also showed elevated coherence.
RF45 AM stabilization looks fishy.
Look at feedback signal (Ch3) VS the range. They're in sync today (left) as well as back on 10th of Sept. (right).