The main aim of the shift was to further study the CARM offset reduction process. Additionally, a new and faster sequence to lock the arms and to find the CARM offset has been succesfully tested.
We first aligned the green beam in the North arm cavity using the galvos. The corresponding BPC setpoints are:
- TILT X= -0.144, Y=-0.3
- SHIFT: X = -0.663, Y = -1.035
This allowed to lock both the North arm and West arm green lasers at 16.00 UTC.
We then unlocked the arms and misaligned the end mirrors to proceed to the prealignment of the CITF. Once reached a good alignment we saved the working points andput the CITF in misaliged state and realigned and relocked the arm green lasers.
After some attempts we successfully implemented a new green arm locking procedure, which allows to handoff the arm control directly from the single-arm IR loops to the green CARM and DARM loops. This procedure also allows to find the CARM and DARM setpoints correspondent to the IR resonance before handing off the arm control.
The new procedure still needs some automation refinement but can be executed as follows:
- Lock the arms on the IR using metatron.
- Put the ALS nodes in locked state and lock the fast loop
- Open the CEB flip-mirror and check the superposition between thereflection LSC_ALS_C/DARM_REFL and the beating ALS_CEB_C/DARM_FREQ signals
- Set the LSC_CARM_SET and LSC_DARM_SET to the current values of the ALS_CEB_C/DARM_FREQ signals.
- run the new change_carm_darm_test() function in the carm_darm_green_m.py script and then IMMEDIATELY put the IR arm nodes in DOWN (to avoid metatron attempting a relock of the IR).
- handoff carm and darm to the beating signals and enable the boost as usual.
- fine tune the CARM and DARM setpoints if necessary.
A further change migh allow the handoff directly to the beating signals, skipping an additional step.
Since the lock of the green loops was still unstabled and unlocked avery few minutes, a finer tuning of the North arm alignment was required at 19.20 UTC. This allowed to mantain the lock for the rest of the shift.
At 19.43 UTC the new locking procedure was completed with success in 4 minutes (see figure 1). Then 10 kHz of CARM offsets were added to allow the lock of the CITF.
Since the changes to the arm lock procedure took more time than expected, a realignment of the CITF was done and we were able to lock the arms with DRMI around 20.40 UTC for 20 mins.
In order to monitor the UGFs, we adjusted the amplitude of the the lines. Then we tuned the gains of MICH, PRCL, and SRCL to tune the UGF to the stable values(see fig 2).
We then proceeded handing off to 3f signals, we immediately unlocked the DRMI. A few seconds later the arm loop (that had been locked for more than one hour) also unlocked(see fig 3). It is not yet clear if this unlock was triggered by the CITF unlock or it happened by random coincidence.
At the end of the shift, we put the green lock down, PR and SR Parked ,and locked the arms on IR.
