J. Kissel, C. Vorvick

While Cheryl and I were aligning the IMC this afternoon, we noticed that we were getting much faster fringing than we saw yesterday. However, comparing spectra of all suspensions in HAM2 / HAM3, in L, T, and V from yesterday evening after work (2017-11-07 02:20 UTC) vs this evening after work (2017-11-08 00:20 UTC) show that there is a large, high Q feature at ~11.3 Hz. Comparing the spectra from over the weekend, in which HAM2 was unlocked, it becomes obvious that the problematic feature dominating the RMS is the HEPI cross-beam resonance, transmitted directly through the locked platform.

Our best supposition is that yesterday, the lower frequency motion (0.5 Hz < f < 5 Hz) was much *larger* than it currently is, dominating the RMS velocity of the IMC, resulting in slower fringing.

So, we'll think more about how we can slow the suspensions down enough to get alignment done tomorrow.