The aim of the shitf was to reduce the thermal transient between the lock acquisition and carm null.
In particular, we had noticed that the change in the optical gain of the DIFFp was too high and the servos were not fast enough to compensate for it (as in the 1st plot, which shows a lock acquisition of yesterday night in which the DIFFp TY gain increases from 0 to 50 in 2 minutes). To minimize this effect Ilaria tuned the CHs (1st part of the shift).
CH to minimize the changing in the DIFFp gain @CARM 0 1f:
- the starting values were:
WI CH: 51 mW
NI CH: 115 mW
At 08.17 UTC, the CH power change (-10 % on both CH powers) has been completed in CITF:
WI CH: 46 mW
NI CH: 104 mW
At 08.40 UTC, we resumed the lock acquisition to see the effect in CARM NULL1F. We noticed that the excursion in the gain has decreased and the transient time has increased, as seen in fig. 2.
We thus left these CH power values.
The second part of the shift was devoted to the increase of the amplitude of the DARM line at 74.4Hz, since we found out that the SNR of the OS is very low and the SRCL SET oscillates.
Increase of the DARM LINE at 74.4Hz by a factor 2
- We started by opening the SR TY and SRCL SET loops (since the calibration of the DCP and OS are based on the DARM line and would change with its amplitude).
- We increased the DARM line amplitude from 2.5e-8 to 5.0 e-8
- We recalibrated the DCP signal both in ASC and LSC processes from 36.4 to 72.8(LSC_MONI.DCP_cali and ASC_pre.DCP_Cali) and closed again the SR TY loop
- We recalibrated the OS, os_cali_science in the ini file, from 35700 --> 7140 (LSC_NArm_B7_OS_I_Hz.NArm_B7_OS_i= 7140) and closed again the SRCL SET loop but with a lower gain srcl set weight from 1 to 0.5 (LSC.SRCL_SET_INPUT.OS_LF_Hz_SIGN=0.5)
- we wanted to try the whole lock acquisition but we unlocked twice in LN2 (unlocks probably due to the NE, similar to the one spotted in 63540 and 63506)
