Tonight I made a measurement of our contrast defect at 430 kW with the latest ring heater and CO2 settings (using Craig's excellent scripts). ETMX RH: 1.4W, ETMY RH: 1W, CO2s are 1.7W as before.
Our contrast defect is about 2.2 mW now.
This measurement has caused some locklosses. The causes seem to have come from two places: the location of the band stop filters in DARM2 that are activated for the PCAL lines and the tramp for changing the darm offset. Dan put some checkers into the code to check that the bandstop is correct. I ran this measurement using a tramp of 2 seconds that I changed by hand (0.3 seconds causes a large glitch). Before I ran the measurement I checked that at this power and with the high violin modes we could step up to a darm offset of 9 pm. As always, this should be checked before running the code.
Unfortunately the results from this measurement might be a little confusing as they were taken about 1.5 hours after the last ring heater change, and during the previous 3 hours many different ring heaters changes had been made. I will try to redo this when the ring heaters have been more static.
I also made a frequency noise injection last night, right before I made the contrast defect measurement. I have attached the plot comparing the gray trace with past measurements. I made one error: I forgot to turn off LSC feedforward before the measurement, hence the lower noise at low frequency. At high frequency, the noise is not any worse than where we have been operating recently, but not as good as it has been in certain configurations. This suggests we need more CO2 annular tuning perhaps, in addition to improving the ring heater configuration.
I have generated a more simplified plot that gets across our important TCS and power settings. This is still a bit confusing because some traces have LSC feedforward ON and others OFF. I recommend looking only about 300 Hz at these plots.
Our "best" frequency noise configuration was at 60W input power and 1.1 EX RH and 0.9 EY RH (green trace). However, this was not a workable solution due to PIs, so we stuck with the second best configuration which was 1W each on ETM ring heater at 60W (yellow/orange trace). For both of these settings, the CO2 lasers were misaligned to the beam and set at 4.0W CO2X and 1.7W CO2Y annular heating.
Then, the CO2s were realigned to the beam, and Dan found the best CO2 configuration was 1.7W annular on each. This brought us to the red trace, still 60W input and 1W each on ETM ring heaters. Now we are at the purple trace, so slight improvement from where have been at 60W. Purple is 76W input, with the 1.7W CO2 settings, and ETMX RH set to 1.3 W and ETMY RH set to 1.0 W.
Here is a handy table summarizing all of the details related to the traces in the attached plot. Some of these measurements have contrast defect measurements to match, some do not.
Remembering that the differential ETM ring heater was the most beneficial for our noise, we have decided to target ETMX RH at 1.3 W and ETMY RH at 1.1 W. These values are approximately what you get when you increase the "best" 60W settings by 25%. These are the current settings as of posting this comment.
| Date | Input Power (W) | X arm Power (kW) | Y arm power (kW) | ETMX RH (W) | ETMY RH (W) | ITMX RH (W) | ITMY RH (W) | CO2X (annular) (W) | CO2Y (annular) (W) | Trace color | Notes |
| 2023-02-24 | 60W | 384 | 387 | 0 | 1.4 | 0.44 | 0 | 4.0 | 1.7 | Blue | LSC FF off, 4.7 mW CD, CO2s not aligned to beam |
| 2023-03-29 | 60W | 366 | 364 | 1.0 | 1.0 | 0.44 | 0 | 4.0 | 1.7 | yellow/orange | LSC FF on, CD 1 mW, CO2s not aligned to beam |
| 2023-03-30 | 60W | 365 | 364 | 1.1 | 0.9 | 0.44 | 0 | 4.0 | 1.7 | green | LSC FF off, CO2s not aligned to beam |
| 2023-04-04 | 60W | 368 | 368 | 1.0 | 1.0 | 0.44 | 0 | 1.7 | 1.7 | red | LSC FF off, CO2s aligned to beam |
| 2023-04-18 | 76W | 435 | 437 | 1.3 | 1.0 | 0.44 | 0 | 1.7 | 1.7 | purple | LSC FF on, CO2s aligned to beam, CD 2.2 mW |
