Sheila, Craig

Summary: This afternoon we were able to finish the CARM offset reduction, and transition to Analog CARM.  We locked with a recycling gain of about 30, although we haven't engaged any alignment servos other than DHARD.  

Details:

DRMI ASC: We tried letting the DRMI ASC come on as writen in the guardian yesterday (with PRM M1 added), it worked once, gave us a nice build up, and was successfully offloaded.  The next couple of times we tried it unlocked DRMI, so we have been skipping it. 

DRMI/PRMI acquisition:  We found that the PRCL gain in PRMI was too high with the better build up (POP 18 NORM ~45), so we have lowered the gain settings in guardian for both PRMI and for DRMI PRCL acquire (was 16, we changed it to 12). We also restored the DRMI trigger levels to what they were in O2. We seem to be acquiring DRMI a little faster like this. 

TR_CARM transition: This has been unreliable for the last several days, our most frequent reason for failure in locking.  We found that the problem was a large transient when the REFL_BIAS (TR CARM) path is first engaged would saturate SRM M1.  We looked at the old version of the guardian and found that this used to be ramped on over 2 seconds, but has been ramped over 0.1 seconds recently.  This transition has been sucsesfull both of the times we tried it since changing the ramp time, in one try there was no transient and in the other there was a transient but we stayed locked.

DARM: In the final CARM offset reduction step we used to reduce the DARM input matrix element (which started at 40) to 8.  We are now reducing the input matrix by a factor of 3 here instead of a factor of 5 for stability.   Attached is a screenshot of the DARM OLG. 

CARM:

• We re-phased the REFL 9 sensor with the single arm locked.   We used the beckhoff controlled phase shifter to shift REFL 9 from 49.7 to 5.9 degrees.
• We have transitioned to Analog CARM with 6dB more gain than we used to use.  We have also lost lock when engaging the common compensation (40Hz/4kHz boost) in the common mode board.  
• Craig has a measurement of the CARM OLG he will attach, although we have had difficulty with locklosses when we try to measure this because the 785 has stalled and we loose lock when resetting it. We have also lost lock just by enabling the excitation on the common mode board.

Recycling gain: We also re-normalized the arm transmission channels at the start of the day, so that we can trust them better.  We have build ups around 1000x the single arm builds ups when we lock, this is how we estimate that the recycling gain is around 30.  (Note that we haven't tried any alignment).

POP LSC: We started to prepare for transitioning DRMI to POP by making a PRCL excitation and minimizing the signal in POP 9 Q, we changed the phase from -22 to -32 degrees.  We measured the input matrix that we should use for POP 9I to PRCL to be 0.0326 which is similar to our old input matrix of 0.035.  

Violin modes: We had a lock stretch long enough to get a decent resolution spectrum of our new violin modes from 1:40 to 2:20 UTC on August 6th (spectrum attached).  The largest peak right now is at 503.086Hz followed by 503.195 Hz and 501.695Hz. We might need to damp these before we can transition to DC readout.