Lucia, Yoshinori (remotely via phone and zoom), Yutaro (remotely over the phone), Kiwamu,

We repositioned the IPs for both ITMX and ETMX. Also, we repositioned the key stone position of the F1 F3 stages on ETMX.

Although, it is not clear at the moment whether this improved the 0.7 Hz oscillation issue as we still see this mode easily gets excited and lasts for long time.

[Logic behind]

• We suspected that the payload position of ETMX might be a trigger for the 0.7 Hz oscillation that we have been suffering (6685).
  • More explicitly, we were wondering whether the payload had been actually rubbing against some external parts.
• We once experienced the situation in that changing the vertical position of the ETMX GASs somehow reduced the amplitude of this particular oscillation.
• For the reasons, we decided to reposition the IP positions and GAS vertical positions to see if this alleviates the situation.

[Repositioning IPs]

We used the stepper motors to move the IP positions for both ITMX and ETMX. After the adjustment, we confirmed that the IP loops can be still closed without an issue.

• ETMX
  • L: 750 => 750 (we actually set this back in the end because this impacted on the optical lever readout)
  • T:-208 => 0
  • Y: -90 =>0
• ITMX
  • L:340 => 340 (no change for the same reason as that for ETMX)
  • T: 224 => 0
  • Y: 189 => 0

[Adjustment of the vertical position for the GASs on ETMX]

We pulled up the payload by ~1 cm upward in total today. This means that the payload now is higher by 0.5 mm than the position that Fujii-kun established in this past Friday (6611). The value quoted here is that measured by the BF V LVDTs. In the middle of this operation, we noticed that the F3 stage approached a position close to the actuation range of the fishing rod. So we backed it up a bit.

• F1 (F1_LVDTINF_GAS_OUT): 170 => 1200
• F3 (F3_LVDTINF_GAS_OUT):240 => 640
• BF V (BF_DAMP_V_INPUT): 2370 => 3540

Assuming the calibration factors to be right, one can interpret the above numbers as displacement in um.