As part of the recovery effort today we stumbled upon a way that seems to fairly reliable allow us to transition from PRMI to DRMI (we were 3 for 3 today - we'll try again tomorrow). The procedure is: - Let Guardian set up for DRMI locking. - Misalign SRM - turn off H1:LSC-SRCL OFFSET, INPUT and OUTPUT - Let PRMI lock - make sure H1:LSC-SRCL OFFSET, INPUT and OUTPUT are off (guardian turns on OFFSET), and clear history. - Pause ISC_LOCK and ISC_DRMI guardian - Align SRM, wait until it damps down. Today the PRMI always stayed locked in this configuration. - Turn on H1:LSC-SRCL OUTPUT - Turn on H1:LSC-SRCL INPUT. DRMI is now locked. - Turn on H1:LSC-SRCL OFFSET, if desired for mode-hopping suppression
Already done at Livingston a long time ago...
https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=11340
Except this scheme seems much faster than waiting for DRMI...