[Stuart A, Arnaud P]

Damped TFs had been taken on MC2 back in August (see LHO aLOG entry 13346), but had not been processed until now:-

- MC2 M1-M1 undamped TFs (2014-08-11_1091848686_H1SUSMC2_M1_damp_ON_ALL_TFs.pdf)

Before the corner vent, MC2 had been exhibiting 1 Hz Pitch and 1.5 Hz Roll modes cross-coupling into the Vertical DOF, which had been exacerbated when the chamber had been pumped down to vacuum (see LHO aLOG entry 11383). This was suspected due to EQ stops being set too close and rubbing, which is captured in an Integration Issue #847.

After the most recent July corner station chamber incursion, transfer functions taken at Phase 3a (in-air) for MC2 showed no cross-couplings into the Vertical DOF (see LHO aLOG entry 13036). Having now pumped down, the damped Phase 3b (in-vacuum) MC2 M1-M1 TFs presented above, are clear of cross-couplings into the Vertical DOF.

Below is a comparison of undamped Phase 3 MC2 TFs (see allhstss_2014-11-24_Phase3_H1MC2_M1_Doff_ALL_ZOOMED_TFs.pdf), the plot keys are as follows:-

Blue Trace = Model (hstsopt_metal)
Orange Trace = H1 MC2 M1 (2013−05−25_1053525085), Phase 3b
Magenta Trace = H1 MC2 M1 (2014−07−28_1090619695), Phase 3a

The original MC2 cross-couplings into Vertical DOF were present in Phase 3a and then exacerbated going to Phase 3b. However, the recent in-air measurements show absolutely no seeds of a cross-coupling.

Below is a comparison of damped Phase 3 MC2 TFs (see allhstss_2014-11-24_Phase3_H1MC2_M1_Don_ALL_ZOOMED_TFs.pdf), the plot keys are as follows:-

Blue Trace = Model (hstsopt_metal)
Orange Trace = H1 MC2 M1 (2013−05−25_1053543407), Phase 3b
Magenta Trace = H1 MC2 M1 (2014−08−11_1091848686), Phase 3b

Furthermore, back in April, even the damped in-vacuum TFs showed the aforementioned cross-couplings into the Vertical DOF. However, this is again not visible in the recent damped MC2 TFs.

Summary:

The above measurements indicated that there is no longer any pitch or roll cross-coupling in the vertical DOF of MC2 and therefore, that after the July corner station chamber incursion that the suspension is clear of EQ stops rubbing.

This should prove sufficient to close the Integration Issue #847.

All data, scripts and plots have been committed to the sus svn as of this entry.