[Tanaka, Komori]

Abstract:

We measured the DC actuator efficiencies of MCE, MCO, and MCI as follows.
The unit of these values represents the transfer functions from each SUMOUT_L to the IMC optical resonant frequency.

• MCE: (4.39 ± 0.17) x 10^4 Hz/count
• MCO: (3.10 ± 0.12) x 10^4 Hz/count
• MCI: (1.03 ± 0.04) x 10^4 Hz/count

Details:

We calculated the actuator efficiency based on the FSR frequency.
The absolute length of IMC will be measured later, but we assume the length to be 53.3 m at this moment.
We believe it is acceptable because the measurement error is larger than the accuracy of the IMC length.

A cavity scan by MCE is shown in the attached figure as an example.
We injected slow triangle waves, with a frequency of 0.05 Hz and an amplitude of 1000, to each SUMOUT_L to perform the cavity scan.
The FSR intervals have some variations due to the suspension or laser frequency fluctuation.
The variation is estimated to be 4%, so we use it as the relative error.

The factor around √2 between MCE and MCO is reasonable because the incident angles to MCE and MCO are almost 0 deg and 45 deg, respectively.
The difference between MCO and MCI (three times) is not surprising since the new magnets on MCO have a larger diameter by twice.

According to the previous measurement (klog:16678), count corresponding to FSR was 440 at MCE, while that is 128 now.
This discrepancy (3.4 times) might support the difference of the old and new magnets.

We will measure the AC actuator efficiency (for example at 10 Hz) tomorrow.