Ushiba, Komori, Tanaka

Just report. The detail will be posted later

We tried to lock PRFPMI with DC readout. PRFPMI DC lock in PRFPMI_LOCKED_WITH_OMC kept for 6 mins, at most. The cause of the lock loss seems to be saturation of OMC PD by DARM oscilating at ~44 Hz.

Now, LSC_LOCK reached to the LOW_NOISING_PRMI state. However, 20 Hz oscillations in MICH, DARM, PRCL happen at the state (fig.1). Tonight, we gave up today's work. we will leave IFO with requesting the INCREASING_LAS_POWER state 

What we did

• In the INCREASING_LAS_POWER state, the guardian decreases CARM CMS IN1GAIN from -16 dB to -25 dB. However, whenever IN1GAIN got -25dB, both trans. powers drastiacally decrease and then IFO loses the lock. To distinguish the cause by OLTF or by CMS itself, we attempted to reduce IN1GAIN to -25 dB with the 3dB larger REFL power than the nominal value. The same phanomenon was observed in this state. So, there are something with strange when IN1GAIN is -25dB. At any rate, we modified the guardain to decrease the gain to -24dB. 
• PRMI ASC sometimes seems to be not worked, especially PRC Yaw control. PRC1 Y sensor seems to be not observed PR3 Yaw motion. On the other hand, PRC2 Y sensor, which was used at the beginning of O4c, seems to be observed the motion. So we switched the sensor to PRC2 Y. Also, the sign seems to be flipped for some reason. Therefore, we implemented the "-1" into FM2 in the PRC2_Y filterrbank. Then, PRMI ASC seems to become stable.
•  we adjusted the relative gain b.t.w. RF and DC to keep UGF of DARM loop.