Since the power outage where the IMC throughput was reduced, our power normalization has been reducing gains artificially by scaling with the IMC input power, which has increased now to give us the same input power on PRM.  

This is the reason for the apparent change in optical gain, which Elenna noted in 87453 isn't a real change in optical gain in mA/m, but it is a real change in optical gain in DARM ERR counts per meter.  At 2W, the IMC throughput is about the same as it was before the vent since power in the EOM is reduced, the gain scaling that happens in OMC_LOCK and PREP_DC_READOUT aren't much impacted by the power outage.  However, as we power up the interferometer the IMC throughput drops, and we scale gains by the IMC input power request.  This means that we are reducing our loop gains as the IMC throughput drops.  

This power scaling impacts all of our LSC loops, and ASC loops, and would drop all those gains by 3% (60/62).  

This power scaling is done by the laser power guardian, I've added a variable called power_channel that is used everywhere that the power scale is set, and for now I've changed it to 'IMC-IM4_TRANS_NSUM_OUTMON'.   I did not change the channel that is used to check if the rotation stage is giving the requested power, that will still be the IMC input power.  This means that the bootstrapping to adjust the rotation stage should continue to give us the same requested power that it did in the past, and should work even when the IMC is unlocked. 

This should cause an increase in kappa C relative to the calibration that Elenna pushed yesterday.  87520  

If we switch to the IM4 trans channel for this scaling, we will increase all the loop gains by 5% compared to how they were before the power outage.  It might make sense to do this, and add those factors into the loops gains to correct, so that our power scaling is more accurate in the future.  I don't want to do this now since we are having locking difficulties due to microseism and the 1Hz ring up today.