Robert, Mitchell, the vacuum team, the SLiC team

This morning we opened up 3 viewports and inserted dampers in between the baffle and the beamtube wall (Fig. 1). I was able to gently move the baffle, using the ”rails” of the eddy current dampers as position indicators in order to adjust the dampers to return the baffle to its original position. Before/after measurements did not deviate by more than 1/16 of an inch.

I used the laser vibrometer shining through a viewport to monitor the baffle. Figure 2 shows time series for beam tube impulses, indicating that the damping reduced the Q from about 400 to about 20 for the problematic 4 Hz peak. Thus, the cutoff frequency of the scattering shelf during high 4 Hz vibration levels should drop from the typical 50 Hz to about 2.5 Hz (so mostly just the 4Hz peak should remain and not harmonics). The second page of Fig. 2 shows before and after laser vibrometer spectra, which show that the main peaks did not move much, and adds evidence that the baffle is unlikely to be rubbing.

The viewports were closed this evening.