In 89751 we found we could not trust the FC1 top mass osems for an accurate FC1 alignment, we then set an FC REFL iris on SQZT7 to help us capture correct FC1 alignment 89771, as we thought we couldn't trust any stage of the FC1 suspension. But this iris also depends on ZM1,2,3 which is confusing.
Since the FC1 issues this week, we checked that the sliders are working as expected 90466.
We have decided to not use the FC REFL iris to set FC1 as it puts FC1 in a very different position to O4. We will align FC1 using the slider positions from O4. This is as in the December vent, between the O4 under-vacuum and the vents, doors off time, the FC1 WIT channels were within ~10-20urad, see top two rows of table below. Additionally in February when we had our FC1 trouble, we though that we would have been fine if we had never touched the FC1 sliders.
From August to November, the FC1 M3 Pitch WIT drifted between 175 and 195urad so where we are currently at 170urad is not far outside of this range.
| FC1 | Temp (Zone 4 G) |
Pitch | Yaw | ||
| Slider | M3 WIT | Slider | M3 WIT | ||
| Under-VAC, O4, Nov 8th 2025 | 67.6degF | 225 | 195 | -153 | -202 |
| Vented, Dec 9th 08:30 UTC | 71.2degF | 231 | 181* | -153 | -201 |
| Vented, 04 June 2026 16:45UTC When tring to use 89694 (good FC flashes alignment) for ZMs and FC REFL iris for FC1 |
71.1degF | 217 | 169 | 52 | 38 |
| Vented, 04 June 2026 20:41UTC Back to O4 sliders. |
71.3degF | 225 | 170 | -153 | -202 |
* drifted down to 162 over next week
We have put ZM1,2 3 back to their O4 sliders as a starting place, you can see below that the top mass osems say this is not the same location as when under vacuum but we don't think this is trustworthy. We will change these alignments as needed to get the FC beam to retroreflect off FC1.
| To match 89694 (good FC flashes alignment). 04 June 2026, 16:45UTC |
O4 time. Nov 8th 2025, 20:30UTC |
Sliders back to O4 values 04 June 2026, 21:15UTC, plot |
||||
| Sliders | WIT* | Sliders | WIT* | Sliders | WIT* | |
| FC1 P | 217 | 169 | 225 | 195 | 225 | 171 |
| FC1 Y | 52 | 38 | -153 | -202 | -153 | -202 |
| ZM1 P | 530 | 420 | 0 | -390 | 0 | -253 |
| ZM1 Y | 0 | 417 | 0 | 432 | 0 | 429 |
| ZM2 P | -429 | -399 | -196 | -273 | -196 | -183 |
| ZM2 Y | -132 | 184 | -235 | -43 | -235 | 101 |
| ZM3 P | -474 | -422 | -190 | -68 | -190 | -57 |
| ZM3 Y | -367 | -282 | -300 | -463 | -300 | -261 |
*WIT is M3 WIT for FC1 but for ZMs there is no bottom mas WIT so we're using M1_DAMP_{P,Y}_INMON
