Oli Patane, Josh Smith, with input from Robert Schofield and others, 


In O2 there was a somewhat common type of glitches called “scratchy” or “blue mountains” that seem to have been related to the swiss cheese baffles at LHO (and likely also LLO). On May 9, 2017 rubber cork dampers were installed at MCA1 at Hanford to damp the swiss cheese baffle (alog). Here we show that this increased the repetition rate of the bright spots in each scratchy glitch, but decreased how often scratchy glitches happen. We also show that scratchy glitches happen much less often at L1, but roughly match the spots per second rate of H1 pre-damping. 

For H1, we compared all the H1 Scratchy glitches identified by GravitySpy Machine Learning (using the ligodv-web glitch search tool) from the beginning of O2 to May 9th, to the scratchy glitches identified from that date to the end of O2. 
Fig. 1 shows a typical H1 scratchy glitch before May 2017 and Fig. 2 shows a typical scratchy glitch after May 2017. The glitches before generally have less bright spots per second; before May the average number of bright spots was 11.6/sec, and after May the average went up to 18.3/sec. Fig. 3 gives a histogram showing the distribution of bright spots per second at H1 before and after the rubber cork dampers were installed. 

From this plot, there seems to also be a decrease in the number of Scratchy glitches after the dampers were installed. In the five months from December 2016 to May 2017 H1 had at least 195 Scratchy’s, the three months after the installation only had 60 glitches, when (assuming similar conditions) we might have expected ~117. 

We also investigated scratchy glitches at L1. Fig. 4 shows a typical scratchy glitch at L1. Fig. 5 shows the H1 histogram now including L1. For the entire run, there were only 16 scratchy glitches identified by GravitySpy. Their average bright spots per second was 10.7. This makes sense, considering that rubber cork damping was not installed on the L1 baffle. 

After O2 the central area of the swiss cheese baffles were removed at L1 and H1. We’re looking forward to seeing whether this eliminates scratchy glitches entirely.