Rana, Dan, Georgia, Craig, Hang
We did some ASC modifications for high power:
1). dither loops
We now control both the dc locking points for PRM pointing and SOFT dofs using dithering loops, similar to what has been done at llo. For the soft loops we use ADS PIT/YAW 4 and 5 to servo them to the spot position on the ETMs. For PRM, we dither ITMY using PIT/YAW 3 and then feed back to PRM to control their dc pointing.
For the soft loops, in order to achieve true unconditional stability at low frequencies, we AC coupled the regular SOFT control signals (z at 0, pole at 0.1 Hz). This compensated the offloading to the top mass at 0.1 Hz so the regular SOFT loops is flat at low freqs. For the dithering part, we put a pole at 0.1 Hz which then combined with the integrator at the top mass to form a true 1/f integrator.
The dither loops are now turned on after engage ASC for full ifo.
2). Input matrix decoupling.
Since we have the DC pointing of the soft loops controlled with the dithering loops, we do not need to ensure the TR QPD combos we use is insensitive to TMS drift. Thus we modified the input matrices for some soft dofs.
Specifically, for CSOFT YAW, we changed the input matrix as
| TRX_A | TRX_B | TRY_A | TRY_B | |
| 0.10 | -1.0 | -0.67 | 0.85 | CSOFT YAW (New) |
| 0.684 | -0.322 | -0.591 | 0.375 | CSOFT YAW (Old) |
We also updated the QPD offsets so that when we first engage the soft loops (before the dithering loops being turned on) they could still converge to a decent location.
After changing this matrix, it seemed that we solved the 3 Hz oscillations showed up in common yaw loops.
The next issue we need to consider is the 0.4 Hz oscillation showing in DSOFT/DHARD/CSOFT PIT, due to either loop cross coupling or the dP/dtheta instability. The first step we tried to do was to decouple DHARD from DSOFT. Specifically, we wanted to update the QPD combos going to CSOFT PIT B path which damps the soft mode from 30 mHz to 1 Hz. Our old matrix sees the hard mode signal about as large as the soft mode. Based on some dithering lines Rana set up (starting from gps 1229590287 for more than 1k senconds), we find a new TR QPD combo that rejects the hard mode better
| TRX_A | TRX_B | TRY_A | TRY_B | |
| -0.02015 | 0.0158 | 0.0026 | -0.0876 | DSOFT PIT (New; NOT YET TRIED) |
| -0.1395 | 0.1353 | 0 | 0.0393 | DSOFT PIT (Old) |
We wanted to try this new matrix but accidentally entered it to CSOFT P and caused a lockloss. We have not yet test this new combo again, and not sure if it would solve the 0.4 Hz oscillation.