[Jenne, Sheila, Anamaria]

It took some convincing to get the IFO to lock today.  A big part of the reason that we've struggled to get through the CARM offset reduction sequence is the 60Hz noise.  Sheila unplugged the Agilent from the IMC board (alog 47741), and then we were able to get to high power.  Recall that we found this problem in January (alog 46465), but somehow having it plugged in the past few weeks hadn't been a problem, so we've been leaving it there.  Perhaps something changed on Tuesday, after which we started noticing the 60Hz lines more?  But they haven't been a blocker for locking until ~yesterday. 

After we were able to get to 35W, we started to have trouble with the same 4.2 Hz resonances that Georgia and Craig were fighting last night (alog 47737). 

Sheila measured CHARD_P, since that sees this 4.2 Hz quite strongly, and we determined that it had extremely marginal phase. CHARD is not currently a noise limiter (DHARD is), so we decided to change the cutoff to give more phase, but allow a bit more drive around 20 Hz.  This is new cutoff is now in the guardian for both CHARD P and CHARD Y, although as a consequence we have put CHARD injections back onto the noise budget list to ensure that they aren't limiting us. 

We were also suspicious of LSC-MICH, since it is one of the loops that sees the 4.2 Hz oscillation grow just before lockloss.  However, the lower side of its phase bubble is at 5 Hz not 4.2 Hz.  In any case, it doesn't look like a LSC-MICH instability, but it also does still look as though if we lower the MICH UGF much further (this measurement was done just before lownoise length control), we're going to have problems.  The LOWNOISE_LENGTH_CONTROL state was reducing the MICH gain from 2.8 to 2.5, which would put the MICH UGF at 7 Hz with less than 20 degrees of phase.  As long as MICH FF takes care of MICH noise in DARM, it should be fine to leave the UGF higher.

We also wanted to put the ETMX spot position back to where Anamaria had found the most circulating power, but as was discovered last night this puts too much drive onto the L2 stage of the suspension for the lowest noise coil driver state.  At LLO, they run with the intermediate-level coil driver state for the L2 stages, so we've changed the COIL_DRIVERS state to do the same for us.  So far we don't see an obvious noise impact, but we should check to confirm. This lets us have the better spot position without having the large A2L coupling that existed last night.