[kTanaka, Ushiba, Hirose] PRXARM lock trial Day 4. Continued from klog30115.

We installed the ALS after the PRX lock. As the result, the ALS successfully drew the IR to the resonance point, but the IR handover could not be achieved. The reason is that the IR error signal is input to IN1 of COMMON_CMS and the GR error signal to IN2 of COMMON_CMS. There is no system to cancel the offset of the IR error signal in advance. That makes it difficult when handing over from IR+GR to IR only.

Detail

• Current VERTEX guardian for PRXARM.
  • ETMX_ALIGNED_FOR_PRXARM: Align ETMX.
  • LOCKING_GRX: Request 'ALS_LOCKED' state to Xarm guardian.
  • GRX_LOCKED : State when GRX locked.
  • ENGAGE_ALSX :Did ALS only Xarm like "ENGAGE_ALS_CARM" in LSC_LOCK guardian.
  • ALSX_LOCKED: State when ALSX locked.
  • FIND_IRX_RESONANCE: Find the OFFSET of the SLOWOUTPUT in ALS_CMS where the IR light flashes like "FIND_IR_RESONANCES" in LSC_LOCK guardian. (FIG1)
  • PRXARM_LOCKED_WITH_3F: State when it is fixed to the offset at which the IR light flashes. (The name is under construction) 
  • IRX_HANDOVER : State for handover to IR, under construction: set sign to -1 and gain to 0 dB for the IR RF45 signal coming to IN1 in COMMON_CMS.
• Before requesting in VERTEX, the following is done manually.
  • The initial alignment and tuning HWP in the same way as in klog30115.
  • After ALSX, we request PHASE_LOCK at ALS_FIBX Guardian.
  • We turned the demodulation phase (Phase shifter) of RF45 before turning on IN1 of COMMON_CMS. By turning the demodulation phase, we estimated the possibility to reduce the AM as much as possible. The DC_OFFSET of the RF45 error signal has approached 0, but it is possible that the error signal amplitude is decreasing at the same time..\
• "When IN1 of COMMON_CMS is turned on after IRX_HANDOVER, the loop is closed.(FIG2) It seems to draw in IR, which is very good.
• Handover was difficult. We want to turn off IN2 on GR with IN1 on IR in COMMON_CMS. But we just reduce the GR gain by 1 dB and PRXARM locked down. As reasons for not being able to handover, the RF45's offset cannot be adjusted and the gain of the IR error signal is low.
• Some ideas for what to do next are as follows. But we would like to know if you have any ideas.
  • Resolving the RFAM itself (e.g. turning the EOM polarisation)
  • Transfer function measurements on IN1 and IN2 of COMMON_CMS.
  • Use the RF45 signal used in PRFPMI, which is normalised with the transmitted power of the ARM. This signal goes into ALS summing, not COMMON_CMS. Offset adjustment may be possible.