Elenna, Dan
We wanted to test the original asymmetric CO2 powers we had back at 60W to see if we could get back to lower frequency noise.
Elenna had been doing some steps and measurements and I took over when she left. Elenna had set the nominal requested CO2 in lscparams to 2.7W (which is actually 4W of actual annular CO2) and I was going to come in a few hours later and take some measurements. However the TCS guardians didn't seem to take us there, probably not reloaded. I changed CO2X by hand up to 4W with the aim of coming back a few hours later to do the measurement.
About 1.5 hours later there was a lockloss, PRG became very noisy. Looking at POP_A_RF9_{I,Q}_INMON they both doubled in counts. I didn't measure PRCL gain but maybe this CO2 change in combination with the new fixed thermalisation gain scaler increased it too much.
I didn't get a chance to do the measurements we wanted (contast, spring, frequency coupling) so I've set the nominal CO2X to 2.7W requested and reloaded the guardians. I've set the THERMALISATION guardian to IDLE to see if this will hold a longer lock. I'll come back in a few hours and see how it's doing and try to take the measurements if it survives.
Looking at the lines before lockloss, it seems going back to an asymmetric CO2 setting 4W and 1.7W on X and Y reduces the 200 and 4500 Hz frequency noise coupling a little but increases the 25.2Hz coupling. Arm power is also slightly down by a few kW. This also looks like it will eventually reduce both the optical gain and cavity pole judging by their trends.
I think we have some promising results from this test, although it is mostly inconclusive because we were unable to get well-thermalized data. As an aside, I think many of our locklosses were related to the fact that the PRCL UGF servo trend had been measured at a different thermal state, so it might not have been properly tuned for the new CO2 settings.
CO2X at 4W, CO2Y at 1.7W
Frequency noise: according to this plot it has improved. Keep in mind we are comparing traces later in lock with a trace 1.5 hrs into the lock. However, that is a significant change.
Contrast defect: slightly worse, 2.2 mW again. Same caveat as above
DARM spring: appears improved too, again with caveats. This was measured with the SRCL offset at -165 (nominal)
The frequency noise and DARM spring plots also show the results with CO2X at 2.2W (CO2Y at 1.7W). The results show either no change or minimal change.
I think these results are promising enough that we should keep these CO2 settings in the guardian. Tonight's lock after maintenance we will remeasure these parameters while we thermalize and after thermalization (~3-5 hrs into lock). We will also monitor and adjust the PRCL gain by hand. When we do DARM spring measurements, we will take multiple measurements with different SRCL offsets.
Overnight locklosses reported in alog 68988. One unknown, one from a PI, last 3h lock ended by Tuesday maintainance.
Analysis from the modulation depth test.
Power-recycling gains for sidebands and carrier
9 MHz PRG = 54.6
45 MHz PRG = 27.2
Carrier PRG = 46.2
Reflection ratios for sidebands and carrier
9 MHz reflection ratio = 0.226
45 MHz reflection ratio = 0.316
Carrier reflection ratio = 0.063
| Channels | 9 MHz | 45 MHz | Carrier |
|---|---|---|---|
| H1:IMC-PWR_IN_OUT16 | 0.013 | 0.015 | 0.973 |
| H1:IMC-IM4_TRANS_NSUM_OUT16 | 0.013 | 0.015 | 0.972 |
| H1:LSC-REFL_A_LF_OUT16 | 0.043 | 0.068 | 0.889 |
| H1:LSC-REFL_B_LF_OUT16 | 0.041 | 0.066 | 0.893 |
| H1:LSC-POP_A_LF_OUT16 | 0.015 | 0.009 | 0.976 |
| H1:ASC-POP_A_NSUM_OUT16 | 0.015 | 0.009 | 0.976 |
| H1:ASC-POP_B_NSUM_OUT16 | 0.015 | 0.009 | 0.976 |
| H1:ASC-AS_C_NSUM_OUT16 | 0.190 | 0.509 | 0.301 |
| H1:ASC-OMC_A_NSUM_OUT16 | 0.190 | 0.557 | 0.253 |
| H1:ASC-OMC_B_NSUM_OUT16 | 0.197 | 0.635 | 0.168 |
| H1:ASC-X_TR_A_NSUM_OUT16 | 0.004 | 0.007 | 0.989 |
| H1:ASC-X_TR_B_NSUM_OUT16 | 0.004 | 0.007 | 0.989 |
| H1:ASC-Y_TR_A_NSUM_OUT16 | 0.004 | 0.007 | 0.989 |
| H1:ASC-Y_TR_B_NSUM_OUT16 | 0.004 | 0.007 | 0.989 |
Relative to https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=68696
We seem to be reflecting more 9 and less 45. The 45 PRG has increased to 27. We appear to still have a large percentage of 9 at the AS port