Alexa, Rana, Evan
This afternoon, we spent some time improving the ASC for PRMI.
PRCL (REFL_A_RF9_I→PRM)
We balanced the amplitude response of the segments on REFL_A_RF9. We let PRX swing freely, watched the fringes on each of the four segments, and then adjusted the gains until the responses had more-or-less equal amplitude. This gave a noticeable improvement in the POPAIR_B_RF18 buildup with PRMI locked on 9 MHz.
We wanted to increase the bandwidth of the PRCL loops to about 1 Hz, so that we could then implement MICH loops with a bandwidth of about 100 mHz. To this end, we did the following adjustments:
- We added an f2 compensator (two zeros at 1 Hz, two poles at 55 Hz) to the PRM M2 pitch/yaw locking filters in order to undo the effect of the final PRM stage.
- We added a zero/pole pair (zero at 1.5 Hz, pole at 55 Hz) to the ASC-PRC filter bank, FM6. This is in addition to an exsting 1/f shape using FM1 and FM2.
- We increased the damping gain on PRM M1 to –1.5 for yaw and –5 for pitch (they were –1 and –2 before). By doing this, we were able to increase the UGF of the PRCL loops to about 10 mHz, as inferred from step functions delivered to the PRM alignment.
MICH (AS_A_RF36_Q→BS)
We then balanced the amplitude response of the segments on AS_A_RF36, usig a similar method with free-swinging SRY (and we double-checked using free-swinging Michelson).
With the PRCL loops active, we engaged the MICH loops. Everything seems to work fine for about 1 minutes, until the MICH error signals started to run away.
IMPORTANT: for both MICH and PRCL ASC loops, we now feedback to M2 stage instead of M1.
Guardian
We updated the ISC_CONFIGS guardian script to include a PRMI ASC state. This handles the ASC in/output matrix, the ASC filter, and the suspension feedback to the M2 stage instead of M1. The DOWN state, restores the suspension feedback to M1. Right now, I have also copied and pasted this to the DRMI ASCs, since we expect to use something similar. The old code is commented so we can always revert.
Times
PRMI was locked on the SB with both MICH and PRCL ASC loops turned on from October 25th 2014 00:54:10 to 0:55:30 UTC.
Next
We should measure the full sensing matrix between REFL/AS and PRM/BS, and use it to decouple these loops. Then apply this to DRMI. For DRMI we should include a SRCL loop, and possibly also feedback PRCL to PR2.
Gains (for reference)
ASC-MICH_Y_GAIN = 0.003, ASC-MICH_P_GAIN = 0.003, ASC-PRC1_P_GAIN = -0.03, ASC-PRC1_Y_GAIN = 0.1
We closed the PRCL, MICH ASC loops with DRMI locked. The configuration is the same as above except with the following gains: PRCL1_P_GAIN = -0.006, PRCL_Y_GAIN = 0.001, MICH_P_GAIN = 0.003. MICH_Y_GAIN = 0.003.
We have now closed the SRCL loop with DRMI locked. We are using ASC_AS_A_RF36_I as our signal, and acutate on SRM. We have FM1, FM2, FM6 engaged, and feedback to SRM_M2_LOCK_P/Y, which has the f^2 filter installed a described above. The gains are (P,Y) = (0.3.,1.2). I have attached a screen shot. The DRMI guardian reflects these changes.
With these loops closed, we've now had a stable DRMI for over 2.5 hours. POP18 and SASY90 are both pretty steady throughout with the 6 WFS loops running. We had a coupled HOM hops in the SRC, but they happened for a few seconds and didn't cause lock loss. Some were associated with us turning on excitations or fooling around with the ASC feedback gains.
Measured the LSC loop gains (on the 1f REFLAIR PDs). UGFs are 75, 10, and 50 Hz for PRCL, MICH, and SRCL respectively.
We are leaving it in DRMI with ASC engaged. Please feel free to do some DetChar. Hopefully our Guardian settings and Limits will keep things safe when the lock breaks.