Since POPX PZT rails quite often, we relocated the pzt to the upstream of the second lens which is a -172mm diverging lens. The beam now hits the PZT mirror after POP-BS1, the beam travels to +Y direction (toward the ISCT1 door), passes POP-L2 lens, is reflected by a fixed steering mirror, travels to +X-Y direction and hits POP-X.
This allowed us to make the distance between the lenses and the distance between the last lens and WFS closer to LLO configuration.
| Used to be (inches) | Is now | LLO (D1201103) | |
| POP-L1 to POP-L2 | 16 | 20 | 20 + 1/4 |
| POP-L2 to POP-X | 11 + 1/2 | 12 | 12 |
I flipped the sign of YAW centering for POPX because we now one steering mirror between the PZT mirror and the WFS. I also told Jenne to flip the sign of ASC YAW input matrix element for POP_X.
I decreased the overall gain for YAW and PIT due to the increased effective lever arm due to physical length plus a diverging lens, otherwise the centering oscillated badly.
| Old | New | |
| H1:ASC-POP_X_PZT_PIT_GAIN | 100000 | 50000 |
| H1:ASC-POP_X_PZT_YAW_GAIN | 100000 | -50000 |
Table photo attached.
I measured the PRC2 ASC loops, and increased their gain significantly. I also measured the POPX centering loop and decreased its gain even more than Keita had already done.
The first and second attachments are the PRC2 pitch and yaw loops. Blue is a reference from mid-May, green is what the loop looked like with the old digital gain value but new POPX position, and red is the loop after the increase in gain. Both loops started with a digital gain of -21. Pitch is now -5,000 and yaw is now -10,000.
The final attachment is the pitch centering loop for POPX. I adjusted the gain until the bandwidth was 10 Hz, which is what it had been set to when Keita originally commissioned that loop (alog 27280). I assumed that yaw was pretty similar to pitch, although I didn't explicitly measure it. I changed the DC6 gains to 0.15 for pit and -0.15 for yaw, from 1 and -1 respectively.
These new values are all accepted in the ASC down SDF.