[Ushiba, Hirose, Kataoka, Sugioka]
Abstract:
We performed adjustments for PRMI 1f and 3f. Details regarding the PRMI 3f locking and phasing will be posted separately by Hirose-san.
Details:
PRMI 1f
For PRMI 1f, we completed the phasing, decoupling, calibration, and UGF adjustments.
First, we performed the phasing for POP17 and POP45 by injecting a 100.125 Hz excitation into both K1:LSC-MICH1_EXC and K1:LSC-PRCL1_EXC.
We tuned the demodulation phase to minimize the peaks in POP17Q and POP45I, which resulted in changing K1:LSC_POP_PDA1_RF17_PHASE_R from -141.0 to -96.0(Figure.1).
The initial value for K1:LSC_POP_PDA1_RF45_PHASE_R (57.870) was found to be already optimized.
Next, we addressed the decoupling between PRCL and MICH. These channels exhibit sensor coupling alongside an inherent MICH-to-PRCL actuator coupling.
The PRCL-to-MICH sensor decoupling was conducted by entering an appropriate value into K1:LSC-PD_DOF_MTRX_3_11.
This value corresponds to the ratio of the peak heights in POP17Q and POP45I when exciting PRCL at 100.125 Hz.
The upper left pad in Figure.2 shows the spectrum of MICH signal before and after MTRX adjustment.
Coupling between the MICH and PRCL actuators was also observed, which originated from using only BS as the MICH actuator, since moving BS inherently causes fluctuations in PRCL as well. To eliminate this fundamental actuator coupling, we decoupled the actuators by adjusting the output matrix. The value to be set in K1:LSC-OUTPUT_MTRX_5_1 represents the ratio of the PRCL length fluctuations caused by BS versus PRM. The actuator efficiencies were measured by taking transfer functions from excitations of PRM and BS to the PRY length with PRY locked(Figure.3). Since the difference between these responses was -22 dB, a value of -0.0404—accounting for an additional factor of 2 due to the difference in the BS position's impact on PRCL and PRY—was entered into K1:LSC-OUTPUT_MTRX_5_1. We skipped the MICH-to-PRCL sensor decoupling because it was already sufficiently decoupled.
We then performed OLTF measurements for calibration and UGF adjustments. Sensor calibration was conducted while monitoring the Out-to-In TF, whereas UGF adjustments were made by monitoring the OLTFs, for both MICH and PRCL(Figure.4,5). During the sensor calibration, we updated the INMTRX values and simultaneously adjusted the filter gains to maintain the overall control gain. For the UGF adjustment, we fine-tuned the filter gains,resulting in a UGF of ~20 Hz for MICH and ~40 Hz for PRCL.
All of these parameter changes were updated in Guardian,and the specific Guardian modifications will be detailed in Hirose-san’s upcoming post.
PRMI 3f
For PRMI 3f, we performed the decoupling, calibration, and UGF adjustments following the exact same procedure used for 1f(Figure.6,7,8). MICH was sufficiently decoupled from PRCL so we didn't perform the decoupling.
