Yesterday we noticed that the POS and SIDE eigenmodes were degenerate (with 1mHz spectral resolution). Moreover, the YAW peak had shifted down by ~500 mHz compared to earlier this week, although there was still good separation between PIT and YAW in the Oplev error signals. Ideas were (i) check if EQ stops were not backed out sufficiently, and (ii) look for any fibers/other constraints in the system. Today morning, I inspected the optic again. I felt the EQ stop viton tips were a bit close to the optic, so I backed them out further. Apart from this, I adjusted the LR and SIDE OSEM position in their respective holders to make the sensor voltages closer to half-light. Kicked the optic again just now, let's see if there is any change.
Remaining tasks:
- Check EY table leveling.
- Check EY actuation matrix diagonality using this technique.
- Check that IR resonances are seen (and all the usual pre-pumpdown alignment checks).
- Take close out pictures.
- Heavy doors on, pump down.
If everything goes smoothly, I think we should plan for the heavy doors going back on and commencing the pumpdown tomorrow. After discussion with Koji, we came to the conclusion that it isn't necessary to investigate IPANG (high likelihood of it falling off the steering optics during the pumpdown) / AS beam clipping (no strong evidence that this is a problem) for this vent.
Update 1235: Indeed, the eigenmodes are back to their positions from earlier this week. Indeed, the POS and SIDE modes are actually better separated! So, the OSEM/magnet and EQstop/optic interactions are non-negligible in the analysis of the dynamics of the pendulum. |