The plot shows that the current vibration levels measured by the 6 accelerometers on the PSL table are about the same as on Boxing day during O1. I also checked several other O1 times, and the vibration levels were very similar to the Boxing day levels. With all of the recent work on the chiller and its lines, the recent levels, in contrast, have been changing quite a bit. This log: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=29764, shows a level that was higher than O1 and, most interesting, a level on July 9 that was about a factor of 2 below O1. The vibration level is very sensitive to the flow rate and Jason thinks that the HPO crystal circuit flow rate might have been lower by a couple of l/m on July 9th than it is now (this circuit has the highest flow rate and is the predominant source of vibration, but doesn’t have a flow meter).
For O1 we set the flow rate as low as suggested by Ollie, but the actual flow rate turned out to have been higher than we thought, because of a poorly calibrated flow sensor. Thus it would not be surprising at all if we could beat the O1 vibration levels and still not be that close to the minimum flow limit - I think we should reduce the flow by at least a couple of l/m.
Another source of vibration is the flow fluctuations associated with bubbles in the system. Jeff bled quite a bit of air at the filters under the PSL table today. However, a measurement taken a couple of hours later after the fans were shut down did not show improvement in the table vibration. But I think that there is still a lot of air in the lines and repeated bleeding, along with reducing the air intake, might give us significant vibration improvement.
The observation that the vibration levels are about the same as in O1, and yet the peaks from the top mount on the periscope are about twice as large on IM4 trans diodes, suggests that the resonances of the mount are no longer as well tuned into a valley in the periscope peaks. So I think we could also get some improvement by re-tuning the resonances.
And it also seems that the jitter coupling is larger. Sheila’s thinks not by much more than two, but it seems worth expanding on Sheila’s piezo mirror injections with some table shaking injections.
Robert S., Jason O., Jeff B.
