After reporting that the Pcal Y TX/RX PD noise spectrum looked quite bad with plenty of lines and comb structure, dangerously close to the CAL-DELTAL_EXTERNAL noise floor in a 100 s FFT (see LHO aLOG 48192), some hardware adjustments were made to improve the Pcal Y performance and noise spectrum (see 48206). Thank you for the fast response by Rick, Jenne, Niko, and Sharan!

While the lines in the 100 s long spectra reported in LHO aLOG 48192 were mostly below the CAL-DELTAL_EXTERNAL noise floor, longer integration times used for long-duration searches will eventually see these artifacts. These must be either followed-up in detailed post-processing studies, identified before analyses, or detection thresholds must be raised. For detailed review, see the O1/O2 lines and combs paper https://arxiv.org/abs/1801.07204.

Keith has a nice tool to monitor the noise weighted 1800 s long SFTs produced by Fscan each day (see here for LHO and here for LLO). The last spectra for each day is a ratio of the current day's average ASD with the run average ASD.

I attach yesterday's ratio plot (figure 1) to show that the downward-facing "spikes" indicate reduction/mitigation of some of the lines spotted in the Pcal spectra from the first few days of the run (figure 2).

This definitely helps, thank you! Pcals should be closely monitored throughout the run so that we can either ask for further mitigation or perform triage in urgent situations.