We did not get the factor of 5 reduction in jitter coupling from second loop ISS and PZT servos that I had hoped for, and resonances of the top mirror mount on the periscope are visible in DARM near 300 Hz. Jason and I altered PSL crystal chiller flow rates to see if they affected PSL periscope motion. Figure 1 shows that, indeed, a 2% decrease in flow rate (as low as we could go using the bypass valve) dropped the periscope motion by 8%. Also, a 10% increase in flow gave a 29% increase in periscope motion.

The great majority of the flow is through the unused HPO. A small fraction of the flow is needed for the front-end laser that we are using. We could reduce the flow and probably remove the peaks from DARM if we turn down the total flow while increasing the fraction to the front-end laser.

Robert, Jason