[Matthew Camilla Louis Sheila]
There is concern that the CO2 laser proposed for the CHETA design has enough intensity noise to saturate the ESD preventing lock.
By calibrating the displacement noise projected from CHETA RIN data into counts at the L3_ADC, using the DARM loop OLG and transfer function between DeltaL_ctrl and L3_ADC, we can get a rough estimate of whether we expect the CHETA noise to saturate the ESDs. This is done by looking at the RMS of the cts/rtHz of CHETA noise at the ESD and comparing it to the 25% of saturation level (2^19 counts).
Figure 1 is the loop model for mapping the displament noise (CHETA RIN) to ESD counts, Figure 2 is a plot of the darm olg, Figure 3 is plot of the tf from deltaL_ctrl to L3_adc.
Figure 4 is the projection of CHETA RIN to the ADC counts, showing that we do not estimate CHETA is likely to saturate the ESDs.
Next steps are to see if we estimate CHETA nosie to saturate the DCPDs at different power up stages.
[M. Todd, J. Kissel]
After measuring very low values for the coherence of the channels used to estimate the transfer function from H1:CAL-DELTAL_CTRL to H1:CAL-CS_DARM_FE_ETMX_L3_ESDOUTF_UL_OUT, it seemed better to go to the calibration model and use pydarm to do this calibration instead.
After making this change, the results are slightly more convincing, saying that we still do not expect CHETA to saturate the ESDs on the ETMX test-mass, however it is around 3% of the saturation level (2**19). The python code used to make this analysis as well as accompanying plots are listed below.
We do however worry about CHETA possibly saturating the coils on the L2 stage, as the noise is around 19% of the saturation level (2**19). This will require some more thought/testing. HOWEVER, this is during the Nominal Low Noise state (pydarm models NLN), and during lock-acquistion we expect that with the additional lowpass filters for the actuation stages we could have some more wiggle room with this.
Much of this code utilizes the pydarm model constructed from pydarm_report_H1.ini found at /ligo/groups/cal/H1/reports/20250123T211118Z/pydarm_H1.ini
The details about how to use the pydarm model and the transfer functions it contains can be found in Jeff's alog
Figures:
- CHETA noise calibrated from m/rtHz to cts/rtHz and RMS to compare to saturation limit of ESDs (L3stage)
- CHETA noise calibrated from m/rtHz to cts/rtHz and RMS to compare to saturation limit of L2 coils (L2stage)
- CHETA noise calibrated from m/rtHz to cts/rtHz and RMS to compare to saturation limit of L1 coils (L1stage)
- Transfer Function - deltaL_ctrl to L3_ESD_cts
- Transfer Function - deltaL_ctrl to L2_coils_cts
- Transfer Function - deltaL_ctrl to L1_coils_cts
- Transfer Function - darm_err to darm_ctrl
- Transfer Function - deltaL to darm_err
- Open Loop Gain measurement of darm - pydar
Code:
