As reported in this alog post, we have analyzed the behavior of 287 OSEM channels at Hanford during magnetic injections, and we looked for possible correlations with the peaks that appear in the magnetic coupling function of H1. 

Here we summarize the results from the OSEM channels and the follow-up channels we have analyzed.

Below is the time evolution of all new peaks that appear in OSEM channels during the last six CS magnetic injections in the frequency ranges 80-105Hz and 38-44Hz.

The evolution in frequency of the OSEM peaks from 100.5Hz to 85.3Hz, matches exactly the evolution of the peak in the magnetic coupling function (see here). We also see that two OSEM channels have a peak at 40.9Hz. 

Following the suggestion from Robert Schofield, and since the OSEM channels that are affected by magnetic resonances are located at the power recycling cavity, we analyzed the behavior of the H1:LSC-PRCL_CTRL_256_DQ channel. Below are ASD plots for this channel 700 sec before as well as during the last six CS magnetic injections at H1.

Interestingly, the 100.5->85.3Hz and 40.9Hz peaks appear both outside of and during magnetic injections. This peak is significantly amplified during magnetic injections, which might suggest some form of gain peaking problem.

Following up, we also analyzed the channel H1:CAL-CS_MICH_DQ and below are the peaks that were identified during, before and after CS magnetic injections, with the red horizontal lines representing locations of frequency peaks in the H1 magnetic coupling function.

Here we see that all resonances in the magnetic coupling function between 20Hz and 120Hz appear in this channel during magnetic injections.

More investigations need to be done in order to identify the exact origin of these resonances. 

I. Michaloliakos, A. Matas, Sh. Banagiri, J. Ni, R. Schofield, Ph. Nguyen, B. Whiting