This alog presents the first steps I am taking into answering the question: "what is the calibrated residual test mass motion from the ASC?"

As a reminder, the arm alignment control is run in the common/differential, hard/soft basis, so we have eight total loops governing the angular motion of the test masses: pitch and yaw for differential hard/soft and common hard/soft. These degrees of freedom are diagonalized in actuation via the ASC drive matrix. The signals from each of these ASC degrees of freedom are then sent to each of the four test masses, where the signal is fed "up" from the input of the TST ISC filter banks through the PUM/UIM/TOP locking filters banks (I annotated this screenshot of the ITM suspension medm for visualization). No pitch or yaw actuation is sent to the TST or UIM stages at Hanford. The ASC drive to the pum is filtered through some notches/bandstops for various suspension modes. The ASC drive to the TOP acquires all of these notches and bandstops and an additional integrator and low pass filter, meaning that the top mass actuates in angle at very low frequency only (sub 0.5 Hz).

Taking this all into account involves a lot of work, so to just get something off the ground, I am only thinking about ASC drive to the PUM in this post. With a little more time, I can incorporate the drive to the top mass stage as well. Thinking only about the PUM makes this a "simple" problem:

• we know exactly what the ASC drive is in counts- we just measure the "H1:ASC-[DOF]_[P/Y]_OUT_DQ" channel
• We propagate drive that to each test mass knowing the drive matrix we have set
  • screenshots of the pitch matrix and yaw matrix
• We calibrate this from drive counts to Newton*meters knowing the drive calibration from G1100968
  • for PUM: 40 V /2**20 ct [DAC] * 0.268 mA / V [drive strength] * 0.0309 N / A [force coeff] * 70.7 mm [lever arm], pit/yaw lever arm is the same for the PUM
  • I conveniently chose a time from before the ETMX DAC change to avoid thinking too hard about the DAC counts
• We transform this N*m PUM drive to radians of test mass motion using the PUM-TST state space suspension model transfer function, which is calibrated into real units
  • I did all of this in python, so I used Kevin's exported quad state space model, found here: T2300299
  • I used the damped model which applies the ETMX top mass damping filters

I have done just this to achieve the four plots I have attached to this alog. These plots show the ITM and ETM test mass motion in rad/rtHz from each degree of freedom and the overall radian RMS value. That is, each trace is showing you exactly how much radians of motion each ASC degree of freedom is sending to the test mass through the PUM drive. The drive matrix value is the same in magnitude for each ITM and each ETM, meaning that the "ITM" plot is true for both ITMX and ITMY (the drives might differ by an overall sign though).

Since I am just looking at the PUM, I also didn't include the drive notches. Once I add in the top mass drive, I will make sure I capture the various drive filters properly.

Some commentary: These plots make it very evident how different the drive is from each ASC degree of freedom. This is confusing because in principle we know that the "HARD" and "SOFT" plants are the same for common and differential, and could use the same control design. However, we know that the sensor noise at the REFL WFS, which controls CHARD, is different than the sensor noise at the AS WFS that control DHARD, so even with exact same controller, we would see different overall drives. We also know that we don't use the same control design for each DOF, due to the sensor noise limitations and also the randomness of commissioning that has us updating each ASC controller at different times for different reasons. For example, the soft loops both run on the TMS QPDs, but still have different drive levels.

Some action items: besides continuing the process of getting all the drives from all stages properly calibrated, we can start thinking again about our ASC design and how to improve it. I think two standout items are the SOFT P and CHARD Y noise above 10 Hz on these plots. Also, the fact that the overall RMS from each loop varies is something that warrants more investigation. I think this is probably related to the differing control designs, sensor noise, and noise from things like HAM1 motion or PR3 bosems. So, one thing I can do is project the PR3 damping noise that we think dominates the REFL WFS RMS into test mass motion.