camilla.compton@LIGO.ORG - posted 15:24, Friday 07 April 2023 - last comment - 09:49, Monday 17 April 2023(68491)
Ring heater changes over last 3 weeks.
Summary of ETM ring heater changes in the last few weeks by Dan and Cao with relevant alogs. Initial aims in alog68115
During this time ITM ring heaters have remained at 0.44W for ITMX and 0W for ITMY - alog 67314.
All changes were with 60W input power.
| Date | EX | EY | CO2X | Reasoning |
| 2022/01/14 | 0 | 1.4 | 4.0 | Starting values. See alog 67314 for ring heater changes 2020 to Jan 2023. |
| 2022/03/20 | 0 | 0.4 | To bring the arm modes closer together alog68166 | |
| 2022/03/22 | 0.4 | 0.4 | To bring the arm modes closer together alog68166 | |
| 2022/03/25 | 0.8 | 0.2 | Lots of quick steps here, alog68166. Ran into 14.7kHz PI. alog68165 | |
| 2022/03/26 | 0.4 | 0.4 | Contrast defect and homodyne angle improvement here. alog68166 | |
| 2022/03/28 | 0.5 | 0.4 | ||
| 2022/03/28 | 1.0 | 1.0 | Try to push past 14.7 kHz 68236. Had stable 20+hour lock here. 68166. Great 4.5dB SQZ during this change (RH transient?). | |
| 2022/03/29 | 1.1 | 0.9 | Tried differential step, this squashed mode-separation peaks (yellow trace) but caused 20.862 kHz, PI. 68265 68287 68294 | |
| 2023/03/30 | 1.0 | 1.0 | Reverting differential step, alog68294. This gave reduced optical gain, freq noise and DARM spring. alog68264 | |
| 2023/03/31 | 1.7 | CO2's were changed from in-lock annular values of CO2X 4W and CO2Y 1.7W to both CO2's at 1.7W. 68346. Tests in 68346 | ||
| 2023/04/04 | 1.7 | CO2's were pico-ed to better line up with IFO beam 68391. Tests in 68487 and pending alog. No dramatic wins from CO2. |
Some wins of the Commissioning and TCS teams are below, details in LHO Commissioning Report G2200705:
- Squeezing improved to 4.5dB: alog 68251. Note that we haven't recovered this SQZ level since CO2's were increased (alog68454).
- Found the arm power buildups were better when the mode-separation peaks were at higher frequencies. (Slide #3 or attached image)
- Found PI's at 10kHz, 14kHz and 20kHz (only been able to damp 10.4kHz peak well: alog68379).
- Some reduction in frequency noise above 100Hz. TCS doesn't change it below 100Hz. alog68264 Slide #4
- Reduction in jitter coupling Slide #5 68300
- Reduced DARM offset and homodyne angle 27 -> 11 deg with contrast defect dropped 4.8 to 1mW alog68166 alog68264 and 17% better optical gain. alog68182 Slide #2
- Note for understanding slide #2: Ideal to have the largest optical gain for a given DCPD sum value. This can be achieved by lowering contrast defect (lower minimum) OR a shallower slope achieved by more power in the arms, better mode matching or ASC...
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Since the 1.0W on both ETMs setting, Dan tried some differential steps (alog68664) to bring the two mode-separation peaks closer together and reduce frequency noise, see alog68664.
Plot of settings attached. Currently at 1.3W/seg on ETMX, 1.0W/seg on ETMY. With 76W out of the PSL.
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