Ben M., Louis D., Robert S.

The cryobaffles at end stations were identified as a likely source of the second most dominant scattering glitches at LHO during O3 (after the reaction mass ESD traces) using videos showing scattered light modulation ( LHO: 55927, LHO: 56508 ). Folks at LLO showed that the corner station cryobaffles were also a problem (LLO: 53364) and we identified three cryobaffles at LHO that needed damping, ETMY, ITMY and ETMX (LHO: 56857). ETMY and ITMY were the worst, requiring only about 3 times background motion to be seen in DARM while ETMX required about 6 times background.  We have damped ETMY and ITMY, the worst, as well as ITMX, which didn’t produce noise ( LHO: 59368, 59640, 60376 ).

The figure shows “before” and “after” shaker sweeps. It is difficult to reproduce the “before” shaker amplitude at all frequencies so I show sweeps that have similar shaking amplitude at the resonance that is closest to producing noise in DARM. For ETMY, at 3.85 Hz the shaking level for the spectrogram was about 30 times the no-wind background and was about 3 times the level reached in the labor day wind storm of 2020. After damping, for the same shaking level at 3.85 Hz, I see no scattering noise. There is post-damping noise visible for the 8.7 Hz resonance but this shaking level is about 200 times the level reached in the labor day wind storm so I don’t think it matters.

For the ITMY baffle, I see no noise post-damping at any of the resonances. The microseismic peak, which can increase relative velocity of the scattering surface and test mass differed in peak amplitude by less than 25% for the ETMY and ITMY “before” and “after” comparisons.

The ETMX baffle, that hasn’t yet been damped, required a 6 times increase over background at 4 Hz before I could detect it in DARM (ETMY required only 3) (LHO: 56857). At EX, the labor day wind storm increased noise at 4Hz by a little over 10 times. For the storm this weekend, I looked at EX increases over background and it looked like ETMX cryobaffle noise would have shown up in DARM when the speed was above about 15 m/s. This would happen in about 4% of hours during the year (LHO: 12996).  There is also a possibility that changing alignment could increase the noise from the ETMX baffle, so I still think it is worth damping if we get the chance.