TVo, Sheila, Koji and Jonathan

Today ASC required our attention, so we spent some time on it.  It looks like the combination of moving the spot position on ETMY and phasing AS72 have helped our build ups when the ASC is engaged at 2W, and perhaps the drop off in POP18 is a bit better. 

Dither Phases:

• We found that the sign of the Pit4 dither servo (ETMX->DARM-Xarmsoft feedback) flipped after several minutes at 20W, flipped again as we powered up to 30W, and again after several minutes at 30W. 
• In the next lock we decided to check the demod phase for the dithers at 2W DC readout.  For PIT4 we changed the phase from -25 to +40 degrees by changing the P2L gain and rotating the response into I, we then had to reduce the loop gain from 1 to 0.5.  We also changed the phase on YAW4 from -25 to +20, and reduced it's gain by half.  
• PIT3 (ITMY-> DARM -> PRM) demod phase seemed fine, YAW3 we rotated from -25 to +20. 
• At 2 W, both ETMY dithers had offsets in the Q phase, so that if rotated the phases to maximize the response in I, we would introduce and offset into the loop, so we did not make any changes to those.  However, once we powered up to 30W we saw that the PIT5 loop ran away, and that we actually had better PRC and POP18 build ups for a different spot position (ETMY P2L changed from 2.6 to 3.45).  We checked the phase on PIT5 demod again at this new spot position, and saw that both the Q offset and the response in Q were much smaller than what we had seen at 2 W. We didn't get to explore the spot positions more in that lock because we lost lock either due to an EQ or running away with PIT5.  

Phasing AS72:

• We also noticed that when we engage ASC at 2W, we have been loosing POP18 build up, so Thomas and I moved offsets in SRC1 until we recovered most of POP18 and the POP90 was lower.  We opened the loops and rotated the phased on AS72A so that the DC signals were all in the I phase, then reclosed the loop.  
• With these changes and the change in position on ETMY, we are now increasing our build ups instead of decreasing them when we engage ASC, and it seems that we are not loosing as much POP18 when we power up.  

Engaging ASC/ no more POP QPD feedback:

• We had one lockloss in ENGAGE_ASC when the PRC1,2 and SRC1 gains are increased, which looked to be due to the large transient when we increase the gain in PRC1.  This seems similar to the reason Georgia added a convergence checker 46554
• We are no longer using feedback from the POP QPD to PRM, and using only the dither loop.  We realized that what we are doing with the feedback to PRM didn't make much sense, we were engaging AC coupled feedback from the QPD at the same time as the wavefront sensor loops are engaged, then increasing the gain, then latter turning on the dither feedback when we engaged the soft loops, then turning off PRC1Y after the soft loops are on.  We decided to try leaving out the QPD feedback to PRM completely, this was fine for the engagement and power up to 20W. 
• We did some cleanup of the code in ENGAGE_ASC, moving some set up for the soft loops to PREP_ASC and getting rid of some repetitive or unnecessary steps. 

LOWNOISE ASC:

• We lost lock 3 times due to a 1 Hz instability that looked like DHARD P after going through LOW NOISE ASC.  We manually stepped through the steps in LOWNOISE_ASC the second and third time, and it seems to be engaging the DHARDP 10Hz low pass caused the instability, so we have edited the guardian to use the less aggressive 17 Hz low pass.  The problem seems to be one of the steps that happens before the DHARD_P cut off filte.  We'd recomend stepping through LOWNOISE_ASC manually next time we try to lock, the instability doesn't ring up immediately after any change, so it may be necessary to wait a few minutes at each step to see what the problem is.  
• The code in lownoise asc was a bit hard to read because of lots of unnecessary logic, we have removed some of this including logic for what to do if the input power is above 45W and counter steps that did nothing, the remaining code could still be consolidated. 
•  Hidden in some of this confusing code was a step where we lowered the gain of DSOFT Y, which was accidentally turning the QPD feedback on for DSOFT Y, which we aren't using.  We have taken it out.

PRMI to DRMI transition:

We had an accidental DRMI lock where SRM was badly mis-alinged, and we were able to walk SRM back in without immediately losing lock.  This happened at 0:59 UTC on Jan 22nd, PRCL gain was 8 and MICH gain was 2.8.