The aim of the shift was to characterize the interferometer when locked only on the IR laser (Both the CITF and the ARMS), with a CARM offset of 300 Hz. Additionally, a new filter for CARM and DARM when locked on the IR was developed and implemented.
The shift started with locking the arm cavities on the ALS and adding an offset of -3000 kHz. We proceeded then in prealigning the CITF and locking the DRMI. After some tuning of the gains, the DRMI was locked at 15.05 UTC and a first attempt of carm offset reduction was performed, reaching -300 Hz of offset at 15.13 UTC. The PRCL gain was lowered from 0.15 to 0.8 to mantain the system stable at values lower
We then attempted at 15.32 UTC a hand-off of DARM from the green beating signal to LSC_B7_B8_DC_DIF_NORM but the arms immediately unlocked. The issue was caused by an error in the setting of the setpoint during the handoff.
We proceeded relocking the arms on the ALS system and the DRMI at 17.20 UTC. THis attempt of relocking the DRMI took more than one hour and required a significative reduction of the MICH gain from 1.5 to 0.7 to be performed. Again, the offset was reduced to -300 Hz at 18.21 UTC with the usual reduction of the PRCL gain (0.08).
We proceeded with a successfull handoff of CARM and DARM at ~18.45 UTC after re-measuring the relative gains between the IR and the Green laser signals. The transfer functions can be seen in figure 1. The results were different from the values measured previously. In particular the gain had opposite sign due to the usage of a negative CARM offset instead of a positive one. The relative gains used for this configuration were:
- DARM: 2440
- CARM: 1400
The functions in carm_darm_green_m have been updated to allow for a handoff IR with different gains and to compute automatically the setpoint for the given gain. More details on the changes in the locking scritps will be added in a separate entry.
We then proceeded performing LSC noise injections on all the DOFs. The injections were performed with the DRMI locked, CARM and DARM locked on the IR B7 and B8 signals with 300 Hz of Carm Offset, according to the following table:
|UTC||duration (s)||DOF||Amplitude||Noise FIlter|
During the noise injection, the 150 Hz resonance was clearly noticeable both on CARM and DARM error signals.
We then attempted a further reduction of the CARM offset at 20.10 UTC but an error in setting the setpoints caused an unlock.
In the meantime, a new filter for CARM and DARM has been designed and added in LSC_Acl with the name ALS_Arm_control_IR2. The function carm_darm_ir_filter should enable this filter but has not been tested yet.
Several attempts at relocking the DRMI were then performed (after relocking the arms on ALS) but were unsuccessfull.
We then left the ALS system nodes in DOWN and the arm cavities locked on the IR lasers.