Sheila Dwyer, Heather Fong

During the commissioning period on Wed March 1, we injected an AC 2-Hz signal into the ERM top mass longitudinal damping loop in order to test the scatter/fringing noise that was described in an earlier LLO test (see LHO alog 34224 and LLO alog 31104). The signal was injected into SUS_ETMY_R0_DAMP_L_IN and SYS_ETMX_R0_DAMP_L_IN. We observed noise in the DARM spectra, which appears consistent with scattering effects, and then we removed the noise by adjusting the PITCH and YAW of the ERMs. The attached plots show our results, where each plot corresponds to the different test masses. 

The settings, before and after testing, are the following:

ETMX:
     Before test: PIT = 0, YAW = 100
     After test: PIT = 440, YAW = 260
ETMY:
     Before test: PIT = 0, YAW = 2
     After test: PIT = -200, YAW = 10

After this test, we reverted to the previous settings of the ERMs such that it would not interfere with other commissioning tests, but we would like to save our settings in order to minimize the scattering effects.