In the situation of this morning, lock duration is only about a few seconds in OBSERVATION state.
1. Check the HWP of PSL and REFL
Fig.1. showed the HWP values and actual power for the IMC trans and REFL DC PD.
As shown in FIg.1., 10 W IMC output already acieved in PSL_HWP of 28 (curennt target 40), and REFL_HWP=163 (current 160, it would give larger power to refl table)
I modified the target values of PSL_HWP=28, REFL_HWP=163
2. Check the lock loss reason
I checked the lock loss reason, and found about 40 Hz oscillation in OMC PD A,B and by increasing this oscillation, the PD saturation happened, as always reported by Yuzurihara-san.
3. Trial of damp the ~40 Hz peak using the DHARD_P signal
I tried to damp the 41.61 Hz peak which shown in Fig.2. and Fig.3. using the DHARP_P signal. I checked the oscillator and found 41.61 Hz peak would come from the ETMY.
So I generated the temporal filter in P2 of NBDAMP, but damping itself was not succeeded even I tried to it in several hours.
This test was performed after increasing the laser power to 10 W with PRFPMI.
It would be better re reduce the peaks at 10 Hz vertical first...
4. Search the reason of short lock loss duration
It would be the reason why the lock duration of DC readout is too short would come from the bad alignment of OMC (and maybe larger RMS of DARM error signal)
To solve the reason why the alignment to OMC is not so good.
With discussion of Tanaka-san, K1:OMC-ASC_DOF3_PIT would have large coupling of yaw alignment, so we need carefully treat the DOF3_P.
I kept the LSC_LOCK state to the LOCKING_OMC_FOR_PRFPMI and performed the several iteration of beacom ASC and offload to optic align.
Usually, the DARM offset was about -1.1e-05, but when I changed the offset value to -1.3 or -1.5e-05, OMC can be locked.
But situation didn'change so much.
(change the alignment to OMC is faster than I expected?)
Next :
Search the good alignment point to OMC using the BEACON ASC
The trial of the peak damping of the 10 Hz vertical to reduce the RMS of the DARM error signal.
Tonight, we will keep the IFO of the LOCKING OMC FOR PRFPMI.
Fig.2. showed the beacon signals in LOCKING OMC FOR PRFPMI, and succeeded to lock OMC more than 40 min, so beacon worked well.
We can lock stable with the state of INCREASING LAS POWER, so LSC and ASC would be no problem.
I also tired to change the OLG of DARM, turned on V3 (9.6 Hz) ETMX, change the DARM offset, the situation didn't change.
I checked the oscillation frequency
- from K1:LSC-TRANS_DC_SUM_OUT_DQ: 43.2484 (one sample), 42.559Hz=8.5118*5(5 samples) Fig.1
- from K1:OMC-TRANS_DC_A_IN1_DQ: 43.0879 (one sample), 42.6584Hz=8.53168*5(5 samples)
- from K1:LSC-DARM_IN1_DQ: 42.8117 (one sample), 42.0315Hz=8.4063*5(5 samples)
- from K1:LSC-ASC_PDA1_REF17_Q_ERR_DQ: 43.2484 (one sample), 42.559Hz=8.5118*5(5 samples)
One and Five sample data show different frequencies. So, can this oscillation be from a mechanical resonance or control instability?
Compared with the past several stop and go of the cryocooler, this time tendency seems to be same with the past cases. So, the increase of temp will be expected soon.
We can find the successive stop and go showed the temp reduction at around -43 ~ 42 days at the level of ~ 65K.
