Ushiba, Tanaka

Finally, PRFPMI DC lock was recovered with NeoLASE. 

After Ushiba-san's adjustment of PRCL and MICH loops, we tried to lock PRFPMI with DC readout. We left the IFO with requesting OBSERVATION_WITHOUT_LINES to mointor the stability of the lock tonight

### Phasing RFQPD for PR3 P

In LOW_NOISING_PRMI, PRMI alignment drifted, especially PR3 PIT and IFO lost the lock. We suspected the phasing of RFQPDs for PRMI was bad. Due to this the alignment signal becomes small and also the range becomes small. So we attempted the phasing of the QPDs. At first, We performed the phasing of each segment of REFL RFQPD2 RF45, which is used for PR3 P control by exciting PRCL at 70.875 Hz to maximize each I signal. Fig. 1 shows the medm screen of RFQPD2 RF45 after the phasing. Fig.2 shows the result of phasing. Each I signls of SEG2, 3, and 4 seem to be maximized. But, Q signal of SEG1 was not changed. However, The coherence between I and Q of SEG1 is low. Also, the situation is not changed even though the excitation frequency is changed to 64.875 Hz. So the cause of Q signal seems to be other reason . And the SEG1 I signal amplitude is the same as the others. Therefore, we finished the phasing. After the phasing, PRMI seems not to be drifted in LOW_NOISING_PRMI.      

### turining off NBDAMP for 44 Hz

After phasing, IFO reach OBSERVATION_WITHOUT_LINES, but the lock duration is short, several mins. The cause of the lock loss seems to be the oscillation of 45 Hz (fig.3). the amplitude of the oscillation seems to be blessed (fig.4). if the amplitude become large, OMC PD saturated and the IFO went down. This behaviour seems to be not the oscillation by the control loop but kicking the resonance.  The 45 Hz is close to the pitch resonance frequency of Type A. And there seemed to be NBDAMP P4 for damping 44.5 Hz pitch resonance in all TypeAs. So we turned off their damping control. The oscillation seems to be disappeared. Then, we could keep the lock for a whole.