Kiwamu, Alexa, Koji, Evan
For the past few days, it has been difficult to lock MICH on a dark fringe; the velocity of the BS quickly becomes too high. Kiwamu found that turning down the gain from −500 ct/ct to −200 ct/ct during lock acquisition helps this situation; also, once locked, engaging FM2 and FM3 (rather than FM3 and FM6) seems to have a higher probability of success for keeping the Michelson locked.
Trying to transition to DRMI_1F_LOCKED_ASC in the ISC_DRMI guardian will blow the lock. This appears to come down to the INP1 and PRC1 loops; the others (PRC2, MICH, SRC1, SRC2) can be engaged by hand just fine. INP1 controls PRM and IM4, and PRC1 controls just PRM. I tried locking with lower gain, with opposite sign, with the PRM M1 bleed-off disengaged, etc., but could not close either loop stably. We'll need to take a deeper look at why these loops no longer work.
With DRMI locked on 1f, Koji and I took an RF spectrum of REFLAIR_B, using the −12 dB coupler on the diplexer (as in LHO#14796). This is the first measurement of the RF spectrum of REFLAIR_B after its modification (LHO#14925).
Initial Alignment
We also had some problems running the PRM_ALIGN and SRM_ALIGN via the ISC_DOF guardian. The PRM_ALIGN takes a while to bleed off from the M3 to the M1 stage, and thus to offload. We tried going back to the old version of PRM_ALIGN in which we only feed the wfs back to M1; however, we did not succueed -- a lot of settings had been changed and we could not remember the old configuration; we didn't spend too much time trying to debug. We also ended up aliging SRM by hand which turned out to be faster. We should take some time and look at these scripts since a lot has been changed.
BBPD spectrum taken. -12dB coupling has already been compensated. Note that the removal of one of the BBPD preamps reduced the PD gain by ~20dB.
Condition:
H1:LSC-REFLAIR_B_LF_INMON 17000+/-2000
H1:LSC-REFLAIR_B_LF_OUTPUT 17.8+/-0.2 mW
H1:LSC-POPAIR_B_RF18_I_MON 350+/-5
H1:PSL—PERISCOPE_A_DC_POWERMON 10620+/-20