J. Bartlett, M. Barton, J. Kissel, A. Pele

Catching up on a lot of measurements with overdue aLOGs. Executive summary -- we think the QUAD is free, but we're taking overnight TFs to confirm. The main chain is the problem, reaction chain looks great.

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After initial "release" of H1 SUS ITMX as a wire(re)hang glass test mass, Arnaud had taken a set of transfer functions (2013−09−09) that revealed rubbing. Bartlett then investigated, and found some barrel stops on the main chain (M0) test mass were in contact. Arnaud then took another set of overnight transfer functions (2013−09−11). However, those transfer functions revealed poor results as well, still indicating rubbing somewhere on the main chain. 

Bartlett went in to investigate, and immediate found "face" EQ stops rubbing the front of both the PUM and TST. Once these were alleviated, in order to get a quick turn around Kissel took as set of DTT transfer functions. Though the results showed significant improvement, poor coherence still remain in the 0.5 [Hz] region for most DOFs, and a vertical mode (at 0.51 [Hz]) stuck up in the ROLL degree of freedom. Both raised suspicion that we might not yet be out of the woods. The problem regarding the V feature in the R TF is in this region where the TFs had very little coherence. So Kissel cooked up a (very plausible) story (IHHO), about a locked ISI and lots of air currents leading to lots of vertical motion (especially with the QUAD undamped) which, for a poorly aligned sensors, would result incoherent, common mode (vertical) noise in the differential (roll) transfer function. We've seen this before on many suspensions (and suspension types), and seen it get better and/or disappear both with an unlocked ISI, and when in-chamber.

After some further discussion, Bartlett went back in and re-centered the M0 RT and M0 F1 OSEMs about their flags (which he said were visible mis-centered, if not even rubbing themselves, see LHO aLOG 7752). The feature was certainly reduced after this, but still present (and with even less coherence). To further support the theory of too much ambient motion, we (a) took a (DTT) swept sine TF in this frequency band, which also revealed low coherence (not attached), and (b) took a (DTT) white noise transfer function with the V damping loop ON (ONLY). (a) revealed that even with all the power focused in this frequency region (as Arnaud says it "the best possible drive"), we still were not able to obtain good coherence. (b) Further reduced the feature becomes ill-defined, to a point that it begins to just look like "normal" incoherent noise. Note that we *only* looked at ROLL after Bartlett re-centered the OSEMs.

The first attachment shows the white noise, M0, ROLL (only) investigations, the second attachment documents all of the complete set of M0 TFs we have from 2013-09-09, 2013-09-11, and today (2013-09-12). The third attachment shows that the reaction chain is great.

Because it's "free," we're taking over night Matlab transfer functions, which hopefully will have good SNR on Roll, and it will also allow us to check the rest of the DOFs, to make sure those are still fine.