Sheila, Georgia
Today, in preparation for a possible input power increase later this week, we tried to optimise some of our TCS settings. Following on from previous CO2 steps, we took a small 100mW step up in CO2X power (to 700 mW), expecting the frequency noise coupling to improve like last time. What we saw was:
- Improved RF18 RF90 build ups (very slight) (good, but unexpected)
- Drop in range BLRMS6 (500Hz-1kHz) (good)
- maybe a decrease in BNS range? (bad)
IncreasedDecreased high-frequency frequency and intensity noise coupling(bad)good!
The time series of several diagnostics is shown in the first attachment. (Edit: removed comment about kappa_c and fc since we can't really tell if they are changing). Perplexingly, this is the opposite of what happened when CO2X was last increased. Since then we have change SR3 heater, and the spot positions. I'm also confused about how the frequnecy noise coupling (measured with the noise budget injections) got worse while the BLRMS improved. (edit: see sheila's comment)
Given the frequency noise coupling we decided to then decrease the CO2 power to 500 mW (100 mW less than nominal), and saw the opposite of the effect listed above (second attachment). I think we did not get a chance to remeasure the frequency and intensity noise coupling before losing lock though.
I had a look at some DARM spectra with 500 averages (third & fourth attachments), and it looks like the high frequency noise shows opposite behaviour to the frequency noise coupling we measured. Based on the DARM spectra and buildups I'd suggest we should increase the CO2X power. For now it is back to the nominal 600 mW.
Yesterday I plotted the measured noise coupling inverted, and gave Georgia wrong information about which way couplings changed.
It turns out that the Frequency noise and intensity noise couplings to DARM both decreased with increase CO2 power on CPX, which was the expected result. So it seems like we could change the set point for CO2X to be 0.7W.
