Jenne, Hang, Ketia, Sheila, Kiwamu, Matt, Lisa, Robb, Evan, everyone in the control room...

today we mostly focused on RF centering.  

We made two model changes:

•  normalize the RF centering signals by their sums
•  adding the I+Q phases in quadrature to for each quadrant so that we will not have to worry about phasing 

We noticed that our normal DC centering loops for the AS port have eveloved to a bad state. In the end we have had about 5 degrees of phase margin and 40dB gain peaking in these loops with the nominal settings we used durring O1.  

We reduced the gain and switched over to 90 MHz centering.  The input matrix that resulted in an upper ugf around 2 Hz for all 4 loops is attached.  The next four attachments are OLG measurements of the centering loops, the blue curves are for the DC centering with the nominal settings used for O1, the red ones are with the input matrix shown in the attached screenshot.  

After adjusting the gains of the RF loops, we closed the BS pitch loop using AS36AQ (our normal sensor).  The closed loop response of the centering loop is clearly a feature of the MICH loop with this centering, as the 6th screenshot shows.  When we are on the DC centering, changing the bandwidth of the centering loops didn't change the shape of the MICH loop, but clearly it does with the RF centering, which must be responding to BS.  FOr the time being I turned off the ELF20Hz (a low pass in the centering loops), which gives us more phase and less gain peaking,  so that our MICH loops still seem stable.  This results in the OLG shown in purple in the 6th attachment.  The Yaw OLG is the 7th attachment.  (The MICH digital gains here were 0.8 for pit and 0.7 for yaw, our nominal settings are 0.7 for both, which is probably fine.)

We left the AS36I to SRM loop open and locked the IFO (including the DRMI on POP state which has coil drivers switching and caused problems last week) without any problems.  I checked that the MICH YAW gain was the same in full lock as it was in DRMI.  In engage ASC part 2 a 5Hz low pass is engaged on the MICH loop, this was not stable and blew the lock.  I've commented this out of the guardian for now. The next two locking attempts failed, AS90 dropped as we came into resonance and never recovered, which could be due to the SRC loop being open, or a problem with MICH loop.  I've saved an SDF snap with the current settings as ASC_progress_March3evening.snap

To sumarize changes:

• MICH P and Y FM5 are no longer engaged in ENGAGE_ASC_PART2
• ELF20s are off in DC3 and DC4 loops
• input matrix for DC3+4 is as in the screenshot
• We are manually not letting the SRC1 loops come on.

The next step is probably to open the MICH ASC loops after they have run in DRMI, and check in full lock that the lock point is still good.  It is clear that there is a difference between DC centering and RF centering when we reduce the CARM offset.