[Yuzurihara, TYamamoto, Tanaka, Washimi, Yokozawa, Dan, Komori]
Abstract:
We created a noise budget plot for the DARM sensitivity as of November 2024, without suspension control noises.
The sensitivity can largely be explained by known noise sources.
The critical contributors to the noise are REFL acoustic noise, suspension thermal noise, DAC + coil driver noise, shot noise, PD dark noise, and frequency noise.
Several strategies have been identified to address these noise sources effectively.
Detail:
We analyzed the DARM spectrum taken at 10:30 UTC on November 21, 2024.
Below, we summarize the current noise estimations and the corresponding future strategies to mitigate them.
The DARM sensitivity at most middle and high frequencies can be explained by these noises.
At low frequencies, the suspension control noise and the scattering noise might be dominant sources.
| Noise source | Current estimation | Future strategy |
| DAC + coil driver | - klog:32123
- Text data from TYamamoto-san for the noise with one dewhitening filter.
- The estimation might vary by a factor of 1.8
| - Enable two dewhitening filters (already applied), which is expected to reduce noise by approximately a factor of 2.
|
| PD dark | | - Increasing the trans-impedance resistor to 400 Ω leads to the noise reduction by ~4x.
- Increasing the input power to 10 W, reducing noise by ~3x.
|
| Frequency | - Calculated as the square root of the summation of the CARM error signal and CARM sensing noise in klog:31719.
| - Increasing CARM gain below 1 kHz by updating the boost filters.
- Reducing CARM shot noise by increasing the input power.
- Tuning beam spot positions to minimize sensing noise from input jitter.
|
| Shot | - Using measurement-based shot noise with the DC PD power of 15 mW.
| - Increasing input power to 10 W, which is expected to reduce the noise by ~3x.
|
| Suspension thermal | - klog:32056
- Currently including only horizontal and pitch thermal noises because vertical and roll contributions are negligible.
- The horizontal and pitch thermal noises are comparable.
| - Cooling to 90 K, which has been almost achieved.
- We should reduce the IX miscentering because the pitch thermal noise will be improved by a factor of only square root of the temperature difference if Q-values remain similar.
|
| MICH and PRCL | | - Higher-power operation will reduce these noise contributions.
|
| REFL acoustic | - klog:31279
- Text data from Washimi-san.
- Harmonics of 60 Hz may be overestimated.
| - Most critical noise to improve the BNS range.
- Tuning the beam spot positions like klog:32362 might reduce the noise caused by the input jitter.
- Working inside IFI chamber like klog:32293 will be necessary.
- Measuring the transfer function from the input jitter to DARM is important.
|
| OMC acoustic and length square | | - Higher power operation will reduce these noises because they are equivalent to the shot noise and PD dark noise.
|
These strategies will guide further noise reduction efforts and enhance the overall detector sensitivity.
