Today I was able to drive a line on SRM pitch and yaw, aka SRC1 P and Y, in an attempt to understand how the SRM alignment signal appears in various sensors. Our current configuration has SRM alignment controlled via the AS RF72 signal, which is the beat of the 118 MHz and the 45 MHz.
To do this measurement, I engaged the usual 8.125 Hz notches in the ASC loops, and drove at 8.125 Hz at the SRC1 SM exc point. I measured the signals in the I and Q phase on AS RF72, AS RF45, AS RF36 and POP X RF, which is a 45 MHz demod.
First, it is very hard to drive a large enough signal to even see the line in AS RF72 compared to other sensors. We are currently operating with 1 stage of whitening on RF72, for reference. The attachment shows how the signals appeared in the AS WFS as well as the POP WFS for pitch and yaw.
Once I took this measurement, I looked at the time series of the signals. POPX 45 Q pitch has an offset that corresponds to 1.5 urad of SRM pitch offset. I calculated this calibration factor from my injection: 7.37e-5 SRM pitch urad/POPX pit ct. The POPX Q yaw signal also had an offset, but it was much smaller, only 0.24 urad, calibration factor 3.25e-4 SRM yaw urad/ POPX yaw ct
On June 5, the SQZ team adjusted the SRCL digital offset, and when the SRCL digital offset was zero, the POPX Q offsets corresponded to about 0.09 urad of SRM pitch offset and 0.05 urad of SRM yaw offset (sqz alog).
In the past, we have operated with some SRC1 offset, however, that offset is remarkably small compared to even the dark offsets we have applied to the AS RF72 channels. SRC1 p offset was set to -0.042, SRC1 Y to 0.098, while the four segment dark offsets on RF72 Q are -17.8, 0.2, 2.2, 12.9 (medm screenshot).
Overall, I think we should consider a few things:
- do we need more whitening on AS RF72?
- should we commission POPX 45 Q as the SRC1 sensor instead?
- should we adjust the alignment offsets of SRC1 to offload some of the SRCL offset?
Sheila has suggested we open the SRC1 loop and try stepping the offset while monitoring the buildups, the effect of the SRCL offset on SQZ, and the overall offsets in AS RF72 and POPX Q.
Whatever effect alignment offsets in the SRC are having on the SRCL detuning seems to be much smaller in yaw than in pitch.
To calibrate the AS RF72 signals into SRM angle, we can use these factors:
0.274 SRM pit urad/ AS RF72 pit ct
0.173 SRM yaw urad/ AS RF72 yaw ct
14:46 UTC DRMI is struggling when ASC starts, I'm going to run a manual_IA
At the time of the request for help 10:22 UTC, we were in in CHECK_AS_SHUTTER where it was presumably stuck at SHUTTER_FAIL which I've encountered again at 15:22 UTC. It's been in that state since 09:05 UTC when we lost lock from 25Ws and the SHUTTER GRD reported "No kick... peak GS13 signal = 51.226"
The shutter did not trigger in this last lockloss, it looks like the light heading to the AS port was not high enough to trigger the shutter.
The lockloss_shutter_check guardian check for a kick in the HAM6 GS 13s anytime that we loose lock with more than 25kW circulating power in the arms. In this case we had just reach 100kW circulating power, so the guardian expected the shutter to trigger. This lockloss looks unusual in that there isn't a increase in the power going to the AS port right before the lockloss.
Ryan ran the shutter test and the shutter is working correctly now.
I think that this is probably the result of an usual lockloss happening at somewhat lower circulating power than usual. We should probably edit the logic in IFO notify to call for operator assistance whenever the shutter is in the failed state.
This is OK, the AS port went dark and stayed there for about 70ms or so after the lockloss and there was no excessive power surge that would have caused the fast shutter to be triggered.
The maximum power of ~1.4W was observed ~160ms after the lockloss, which is well below the threshold for the analog FS trigger (3 to 4W, I don't remember the exact number).
If something similar happened with 60W, though, FS might have been triggered.
Attached is the estimate of the power coming into HAM6 using two different sensors (PEM-CS_ADC_5_19 = HAM6 power sensor in the AS camera can which monitors power before the fast shutter, and ASC-AS_A_DC_NSUM after). Neither of these have hardware whitening, neither saturated (ASA was close to saturation but the HAM6 power sensor saturation threshold is about 570W when beam diverter is open, 5.7k if closed).
Note that the calibration of the PEM channel is a factor of 10 smaller than that in the observation mode (0.177W/ct, see alog 81112 and git repo for lock loss tool) because the beam diverter (90:10) was open.
I made a timeline of what ISC_LOCK was doing during this event.