Sheila D., Evan G.

We investigated whether 1080 Hz glitching seen throughout ER10 and into the start of O2 is due to jitter noise. 

It has been seen in various runs on Hveto that a large number of the 1080 Hz glitches are vetoed with channels like H1:IMC-PZT_PIT_OUT_DQ (see, for example, here). Note that the auxiliary channel has glitches over a broad range of frequencies that are used to veto the 1080 Hz glitches.

To test if jitter really could be a culprit, we inject a broadband excitation into IMC PZT YAW and use IMC WFS A DC segment 1 and IMC WFS B DC segment 1 as witnesses for the jitter coupling. In the witness channels, the noise goes up by a factor of 2-4. At the same time, the broad noise feature in DELTAL_EXTERNAL at 1080 Hz basically remains unchanged (see attached figure). It is possible there is some underlying jitter noise at these frequencies (because the DARM spectrum goes up a little at nearby frequencies), but the primary cause of the 1080 Hz doesn't seem to be caused by jitter noise.

We tried excitations in IMC PZT PIT, but this also does not have any effect on the 1080 feature or the glitch level.