Jennie W, Sheila, Jenne D, Tony S,

Summary: PRCL loop seems to be behaving ok. Not sure why we can't lock DRMI.

We were having trouble staying locked in DRMI today so we did some open loop transfer function (OLTF) measurements of the PRCL, PRX and PRY length loops as a cross-check.

Below I include photos of the PRCL OLTF measurement where you can see there is no coherence below 20 Hz and there is a small bump in the measurement between 20 and 30 Hz.

This seemed strange so we measured PRX (state in ALIGN_IFO guardian) and PRY

Steps to lock PRY:

• I misaligned ITMX and aligned ITMY suspensions.
• Jenne D rand the PREP_FOR_PRX state in ALIG_IFO guardian
• then ran altered steps from AQUIRE_PRX state from the guardian terminal to lock us in PRY.

From the OLTF for PRX (brown trace) and PRY (red trace) we can't see any strange behaviour between 20 and 30 Hz in either state.

Finally I compared the PRCL OLTF to a measurement Ryan did a year ago, and from this (red trace) it looks as if that gain bump between 20 and 30 Hz and the rest of the TF shaping is nominal.

For completeness I include the measurement I did of MICH while PRMI was locked.