With Hirata-san.

Summary: the BS optic is 2.8 mm below the average height of the flanges when F0 and BF are close to zero and F1 is alledgely close to zero.

See pictures in the album BS Remedying work after O3.

• Temperature: T_ondotori = 23.6  °C, T_PT100 = 23.6  °C.
• We set the F0 anbd BF GAS fiters at zero with coil magnet actuation:
  • F0: 14,000 cnt,
  • BF: 4000 cnt,
• F1 LVDT is not working well (entry 18191), so we checked the amount of actuation we used the last time we measured the height, when the LVDT was working, and used the same value (entry 17338 from the 30th of June, 2021). This is fine because we have the same temperature today (23.6 °C) and the fishing rod has not been used:
  • F1 actuation: -10,000 cnt (per Data Viewer).
  • F1 LVDT: 787 um (nominal is zero but we have a faulty LVDT primary coil).
• As a reference we used Tomaru-san's marking of the average of the heights of the four flanges of the chamber.
• The measured height to be approximately 2.8 mm below the reference.

With Hirata-san, Terrence and Yano-san.

Summary: We raised the pre-isolator by approximately 2.8 mm and then measured the optic to be 0.3 mm below the height reference.  At the time of the measurement F0 and BF were close to zero and F1 was alledgely close to zero.

See pictures in the album BS Remedying work after O3.

• Temperature: T_ondotori = 23.5 °C, T_PT100 = 23.7 °C.
• According to entry  18710, the mirror was 2.8 mm below the reference, therefore, we raised the jacks (M42 X 2mm thread) by rotating them counterclockwise 1.4 turns approximately. The reference is the average height of the centres of the four flanges.
• Then we set the F0 and BF GAS fiters close to zero and F1 close to 787 um with coil magnet actuation:
  • F0: 13,000 cnt,
  • F1: 10,000 cnt (LVDT readout 788 um becuase there's a problem with the LVDT, real nominal is zero),
  • BF: 4000 cnt.
• Then we measured the height of the optic: it was 0.3 mm below the reference, which is close enough given the methods we are using for the measurement.
• We proceeded with leveling the IP by slightly adjusting the jacks. Bringing L close to its setpoint moved L away from its sentpoint, so we settled with having T closer to the setpoint and do further adjustment with the horizontal fishing rods.
  • L: -710 um,
  • T: 100 um.

With Hirata-san.

Summary: we assessed the height of the optic and chose a suitable position for the F1 keystone.

See pictures in the album BS Remedying work after O3.

• We set all the GAS filters to zero using the control system.
• We inspected the position of the RM screws with respect to the laser level that indicated the desired height of the optic.
• Then, we adjusted the position of the F1 GAS filter keystone in order to have the optic at the desired height. We did this by changing the setpoint of the control system: 572 counts, which corresponds to -400 um with the current temporary calibration factor and offset. The calibration factor and offset will change in the future, but the setpoint in units of counts should still be used.

There are observations:

• The BS recoil mass does not have scratch lines, so we use some vented screws as reference. We can't place a ruler either, so we need to rely on visual inspection in situ and analyze the pictures afterwards. These conditions likely increase the error in the measurement.
• According to the displacement of the left screw, we moved  the F1 keystone down by approximately 0.7 mm, which is a small amount given the reproducibility and error in the measurement. (See first and second pictures.)
• The height of both screws after the adjustment was close to the desired height. (The third picture shows the right screw after the adjustment.)
• The actuation required for this was around -24,000 counts, which is very large.
• T =  23.2 °C ondotori (T_O3GK = 23.0 °C).