[Ushiba, Komori, Sugimoto, Sugioka, Tanaka, Yokozawa, Dan]

Summary

• As reported by Washimi-san on klog30613, when we injected 82Hz at OMC, DARM noise around 100Hz became noisy broadly.
• This may be the coupling with the 82Hz injection and noise around 9Hz, which make a broad noise around 100Hz.
• As there is a small peak noise at 82Hz, we tried estimating the effect on DARM sensitivity.
• We injected 82Hz signal in the OMC loop and with the shaker (klog31343) by changing the amplitude to see the generated broad noise around 100Hz and tried estimating the effect on the DARM from the real 82Hz peak.
• But, as the estimated results were negative values, the measurement error could limite the estimation (or the 82Hz peak is really creating the noise around 100Hz?).

Details

• Injection at the EXC of the inloop filter (K1OMC-LSC_FB_FLT)
  • The diaggui file: /users/Commissioning/data/OMC/2024/1016/SPEC_INJ_82Hz_OMCPZT.xml: Fig001
  • The injected count: 100, 50, 25, 10, 3, 0
  • We looked at 100.125Hz on the DARM_IN1 and recorded the value with the injection counts.
  • Then we used the data for the fitting.
    • Used function was y=ax+b, where x is the square of the injection count, and y is the square of the DARM noise at 100.125Hz. (We used Excel for this fitting.)
    • This is because the function we though is n = sqrt{a + bp^2}}, where n is the noise at DARM, and p is the injection amplitude.
    • Then, we used the function with the estimated parameters to estimate the effect from the real peak: Fig002
  • The result was negative number.
• The shaker was installed (klog31343).
• Injection with the shaker
  • We used the shaker and performed similar measurement as the above.
  • The diaggui file: /users/Commissioning/data/OMC/2024/1016/SPEC_INJ_82Hz_SHAKER_DUCT.xml: Fig003
  • Injection was applied at K1:PEM-EXCITATION_SR3_RACK_4_EXC, which is reported on klog31343
  • The injected count: 100, 75, 50, 30, 10, 0
  • Because the relationship between the injection counts and the DARM noise was not so good, we used the 82Hz peak value at OMS-LSC_ERR as the injection amplitude.
  • Then we used the same function to fit the data and estimated the effect from the real peak: Fig004
  • The result was also negative number.
• From these results, we think the measurement error could limite the estimation (or the 82Hz peak is really creating the noise around 100Hz?).