Kiwmau, Alexa, Sheila
Tonight we were having difficultly keeping DRMI locked stably, so we decided to spend some time looking into it rather than continuing to try locking the arms +DRMI.
First we had a look at our ASC loops. We copied the filters from the OMC QPD centering servos for the AS WFS centering servo, this keeps the beam centerd on the WFS much better. We also had to use the picomotor to steer it a few times because we ran out of range wth OM2. Sometimes our 4 DRMI ASC loop (AS A 45 Q to BS, REFL A 9I to PRM) worked, well, sometimes they did not. We loked again for a signal to use for SRM, (they are using refl B 45 Q at livingston according to 13513) So, far, all of the 45 signals have a large offset. We haven't looked at 36, or AS B since we don't have AS B centered.
We decided to try some TCS CO2 laser on ITMX to see if this would alleviate our mode hopping problem. We tunred the CO2 laser on at 1 Watt. We had DRMI locked with our 4 ASC loops working, however the buildup in DRMI degraded. We then measured the contrast by locking mich on the dark fringe then the bright fringe. 32 minutes after we turned the laser on, the contrast was 97.8%, (worse than what Kiwamu measured 13824) it continued to get worse for the next ten minutes. We then turned off the laser, and watched the contrast improve (kiwamu has the screenshot).
We then looked at G1401119, to gues that we need about 370/572 of the laser power that livingston uses, ( 14673), so we set the power to 180 mW, according to H1:TCS-ITMX_CO2_LSRPWR_MTR_OUTPUT, which is a requested power of 0.12 and an angle of 45 degrees on the rotation stage. (we set this at 8:09 UTC on october 16)
Here are some lockloss times for DRMI 2:51:29 UTC 2:57:07 (arms were locked with ALS)
DIFF 2:34:40 2and 2:37:20 UTC all of these times are october 16
Here is the evolution of the dark port while the MICH has kept locked.
This morning the contrast was 99.84% (bright 4594 counts in AS air LF, mich dark 2.6 counts, dark offset -1)
Alastair and I walked through the calibration of the H1:TCS-ITMX_CO2_LSRPWR_MTR_OUTPUT readback, last night it was calibrated in volts, but I had assumed this was Watts. It turns out that this is close to correct. This means that our power has been about 0.193 Watts on compensation plate since 8 UTC this morning.
The calibration from watts at the compmensation plate to volts at the ADC is:
(1 Volt at ADC/1mV at power meter head)*(1Watt onto power meter/1.878mV out of power meter head)*approximately 2 Watts at CP per watt at power meter head = 1.06 Volts at ADC/Watt at compensation plate.
Greg also sent numbers for the power he measured at the base of the persicope using a power meter, he found the minimum powerto be 0.05 Watts at 37 degrees on the rotation stage, and the max power 5.41 W at 82 degrees. I entered these into the rotation stage calibration screen, based on this we would think we have 0.154 Watts at the bottom of the periscope.