daniel.brown@LIGO.ORG - posted 17:27, Thursday 13 April 2023 - last comment - 11:02, Monday 17 April 2023(68664)
Differential ETM heater step
I have just stepped ETMX up by 0.1W. I will later do -0.1W on ETMY.
Moving one arm at a time to see if a particular change hits the 20kHz PI or not. Hopefully it won't now as we're operating at different ETM RH and circulating powers.
Comments related to this report
daniel.brown@LIGO.ORG - 11:03, Friday 14 April 2023 (68676)ISC
Ring heaters are currently at ETMX = 1.1W ETMY = 1.2W.
Contrast defect has increased slightly to 1.6mW (up from 1mW (68166)) with an arm power of 430kW
Back around April 1st we had about 365kW arm power, sqrt(430/365) = 1.08, so we should see an 8% increase in optical gain from that time. However for ~23mW we are only seeing a 5.5% increase. If we were running at 40mW we would have seen ~6% increase from April 1st.
Caveat to this measurement, we were only about 1 hour in to a lock so still some thermalisation going on. I've had some issues running this measurement and losing lock. I reduced the highest DARM offset and started from the smallest to the highest value this time and switched off the 250 Hz LSC lines this time.
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daniel.brown@LIGO.ORG - 14:55, Friday 14 April 2023 (68687)
Tried to measure the contrast defect just now and it caused a lockloss again due to a large glitch in the DCPD, despite only going up to 30mA sum. Next time I'll try a slower X0 TRAMP to see if that helps.
The TEM00 contrast defect measurement doesn't make much sense and is now predicting a 3 or 5mA defect, unclear how much to trust this. The two cal lines are no longer predicting similar defects in size or location which is a sign something probably went wrong with this measurement so I will need to retry it later this week.
The ETM RHs are affecting the PRCL gain too. More ETMX brings it up, whilst less ETMY appears to bring it down. As I've been stepping ETMY down this may have contributed to the increased PRCL issues the last few days. The opposite is true of carrier PRG.
Ring heaters are currently at ETMX = 1.1W ETMY = 1.2W.
Contrast defect has increased slightly to 1.6mW (up from 1mW (68166)) with an arm power of 430kW
Back around April 1st we had about 365kW arm power, sqrt(430/365) = 1.08, so we should see an 8% increase in optical gain from that time. However for ~23mW we are only seeing a 5.5% increase. If we were running at 40mW we would have seen ~6% increase from April 1st.
Caveat to this measurement, we were only about 1 hour in to a lock so still some thermalisation going on. I've had some issues running this measurement and losing lock. I reduced the highest DARM offset and started from the smallest to the highest value this time and switched off the 250 Hz LSC lines this time.
Stepped ETMY down to 1W per segment.
From the steps last night, dropping ETMX increased the PRCL gain but dropped the PRG, ETMY seems to do the opposite.
ETMY 1W ETMX 1.3W
Tried to measure the contrast defect just now and it caused a lockloss again due to a large glitch in the DCPD, despite only going up to 30mA sum. Next time I'll try a slower X0 TRAMP to see if that helps.
The TEM00 contrast defect measurement doesn't make much sense and is now predicting a 3 or 5mA defect, unclear how much to trust this. The two cal lines are no longer predicting similar defects in size or location which is a sign something probably went wrong with this measurement so I will need to retry it later this week.
The ETM RHs are affecting the PRCL gain too. More ETMX brings it up, whilst less ETMY appears to bring it down. As I've been stepping ETMY down this may have contributed to the increased PRCL issues the last few days. The opposite is true of carrier PRG.
Frequency noise appears better today as well with these differential RH changes, although it seems more steps could be made. HOM peaks are slowly coming together with these steps.
Does this mean we should set the ETMX ring heater to ~2 W?