[Ushiba, Komori]

We performed the noise budget of the locally-controlled degrees of freedom, which is MN Length, Pitch, and Yaw of the four test masses, in addition to IY MN Roll.

We used the DARM spectrum around 0:30 in 10/14.
The transfer functions from each degree of freedom to DARM were measured in klog22495.
The noise of those during the similar period when the DARM spectrum is taken were measured in klog22500.

The first figure shows the projection of all degrees of freedom.
The second one focuses on the dominant sources in the frequency range of 10-50 Hz, where the transfer functions were measured.

Discussion

• The total budgetted noise (black line) is close to the measured DARM sensitivity around 10-25 Hz.
• The most dominant sources are EX MN Length (blue) and IX MN Pitch (green). These seem to limit the current sensitivity. The noises of them are relatively larger than others.
• The subdominant noises come from other MN Pitch modes (magenta and cyan). The gain of the transfer function is larger than Length and Yaw modes.

We should decrease the noise of the local control of EX MN Length and IY MN Pitch at first.
Also, it is necessary to reduce the pitch coupling of all test masses to enhance the DARM sensitivity more.
The coupling from the DAC noise should be considered.