This is an alog about the (aborted) attempt between Saturday and Sunday to make the interferometer work at 0.43 W of TCS power.

The locking sequence was fine up through the dc readout step. However, the interferometer would lose lock at 10 W or higher. We've seen this kind of behavior before, and the culprit is usually the SRC1 yaw loop. I rephased ASA36 by driving SRC1 yaw at 0.3 Hz. Segements 3 and 4 (the two that we're using) both gained 25°. Segments 1 and 2 still have less signal than 3 and 4, which is what we saw before. At the end of the night I reverted these phasings. I also redid the dark offsets on these segments, and have left them there.

Rephasing ASA36 didn't seem to fix the problem, so I went through and rephased Refl A 9, Refl B 9, AS A 45, Refl A 45, and Refl B 45. For Refl 9, I drove cHard at 8 Hz in pitch . For Refl 45, I drove PR3 at 9.1 Hz. For AS A 45, I drove dHard pitch at 8 Hz. Many of the original segment settings were so far off in phase that I suspect they are bad even at the lower TCS power, so I did not revert these new settings at the end of the night.

I also looked into the subtraction of the Refl 9 signal from the PRC2 loop by driving cHard in pitch again. The ratio of the signal in the 45 MHz and 9 MHz WFS was Refl A 45 / Refl A 9 = −0.79 and Refl B 45 / Refl B 9 = −0.76. Our current subtraction settings in the input matrix assume a ratio of −0.60 for both A and B. We should recheck this at the lower TCS power and update the Guardian settings.

Finally, I looked at rephasing the LSC in full lock. I drove PRCL at 136 Hz and then rotated POP9 from 90° to 95° to minimize the apperance of the line in POP9Q. I repeated this for SRCL, but no rephasing was required. However, the subtraction of POP9I into SRCL was quite bad. I drove PRCL again while watching the SRCL error signal, and based on this I changed the matrix element for POP9I→SRCL from −0.04 to −0.012. This setting is in the Guardian (and should be rechecked at the lower power).