KAGRA Logbook

Reports 1-1 of 1

MIR (EX)

kentaro.komori - 22:49 Saturday 09 December 2023 (27902)

EX Q-measurement

[Komori, KYamamoto]

We measured the Q-value of an EX mechanical mode and reconfirmed the resonant frequency and Q-value of the fundamental drumhead mode.
The results, based on 10 measurements, are as follows:

- Resonant frequency: 21.07462 kHz
- Q: (1.84 ± 0.23) x 10^5

- Resonant frequency: 23.6928 kHz
- Q: (1.07 ± 0.04) x 10^5

For the time being, please use this frequency as the beacon sideband.
This frequency differs by 2.6 Hz from the previous report (klog:27634).

This discrepancy might be due to the fact that the peak of the transfer function does not precisely indicate the resonant frequency because of beating with the injection frequency.
However, the actual resonant frequency might indeed be changing, as reported in klog:27893.

Images attached to this report

Non-image files attached to this report

Comments to this report:

kentaro.komori - 23:24 Saturday 09 December 2023 (27912)

From this measurement, I began using the improved Python code for Q-measurement (/users/Commissioning/Q_meas/Qmeasfit.py).
The main difference is a reduction in the number of fitted parameters.

In the previous code, the excitation period was included in the fitting, and the moment when the ringdown starts was one of the fitted parameters.
This setup led to frequent fitting errors due to the fluctuating excited amplitude.
Therefore, I excluded the excitation period from the fitting region and removed the moment when the ringdown starts from the fitted parameters.