camilla.compton@LIGO.ORG - posted 11:07, Wednesday 22 March 2023 (68115)
TCS Tuning Hopes and Dreams
alog documenting words of Dan and Cao
On Monday Dan reduced the ETMY RH from 1,4W to 0.4W (alog 68082). This has already brought the X and Y mode separation frequencies much closer together. See attached: blue plots are before the change, and pink plots after the change, 30 minutes and 1 hour after max power is reached.
Current TCS settings are Ring Heaters: IX 0.4W, EX 0W, IY 0W, EY 0.4W. CO2: When we have IFO input power 25W and higher 1.7W IY Annular and 4.0W IX Annular, 0W when IFO input power is <25W.
Tools that might be useful over the coming weeks:
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/opt/rtcds/userapps/release/tcs/common/scripts/power_adj_scripts/ring_heater_schedule.py To change RH powers automatically, used in alog 67327
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/opt/rtcds/userapps/release/tcs/common/scripts/power_adj_scripts/co2_power_stepper.py To step CO2 over a range of powers, used in alog 66781
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PI monitor with the X and Y modes on are accessed through sitemap > PI > ! DTT Templates. Some details about these from Dan are in alog 67393.
Ideal plan moving forward:
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Change ETM ring heaters to bring the Y and X mode separation frequencies on top of each other. The PI template is looking at the 2nd order mode frequencies (1st order is near 5150Hz). As the arm powers increase we expect the modes to move up so it's not super simple plus this changes ASC and everything else.
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Once we have the separation frequencies the same we will want to reduce mode mismatch by reducing the separation frequencies peak so it disappears. This should be done with more ETM RH tuning. Maybe some ITM RH would be needed to.
Looking at Dan's mismatch plot, step one (overlapping the modes) would bring us to the 0Hz mode-separation diagonal line. Then step two (squashing the modes) would bring us to the middle mode mis-match contour and then we would have perfectly mode matched the arms to each other...
Images attached to this report
