With Ushiba, Tanaka

Summary

• As reported on klog31507, the interferometer was not stable because of 1.1Hz oscillation, we tried reducing it by the adjustment of ASC control filters.
• DHARD_P, DHARD_Y, CHARD_Y, DSOFT_Y filters were adjusted.
• Then, the 1.1Hz oscillation on the control loops was reduced.

Details

• We checked when the 1.1Hz oscillation appeared by changing the LSC_LOCK state and ASC_LOCK state and found the ASC loops seemed to make the oscillation.
• So we adjusted the control loops of ASC.
• OLTF measurement and filter adjustments for ASC
  • State: LSC_LOCK = PRFPMI_RF_LOCKED, ASC_LOCK = PRFPMI_ASC_ENGAGED
  • DHARD_P
    • Adjustment for K1_ASC_DHARD_P loop by using K1_ASC_DHARD_P_OLG.xml
    • Added -3.3dB to move UGF to 0.3Hz
  • DHARD_Y
    • Added -4.8dB to move UGF to 0.6Hz
  • CHARD_P
    • Because the suppression did not change, we did not change the filter.
  • CHARD_Y
    • Added -0.6dB
  • DSOFT_P, CSOFT_P
    • Because these UGFs are too low, we did not adjust them.
  • DSOFT_Y
    • Changed Q of 1.7Hz from 2 to 1.3
    • Added a notch(1,2,10)
  • CSOFT_Y
    • Looks fine! -> We did not change the filters.
  • The results are attached.
    • Red line is the adjusted result and blue line or green line is the measurement before adjustment.
    • The improvements on DHARD_Y, DSOFT_Y seem to be large.