Abstract:
I checked the mechanical transfer functions of ETMY and found that GAS F1 is not healthy.
I asked Takahashi-san to investigate the problem.
Detail:
Figure 1 and 2 show the TFs when exciting from F1 GAS at present and previous in-air health check (klog20729), respectively.
Obviously, current TFs are strange.
So, I asked Takahashi-san to check the GAS status.
At MN and IM stage, TFs of all 6 dgrees of freedom seems fine (fig1 to fig12).
After several investigations, we found that F1 GAS seems rubbing, so we moved it down by about 200 um.
Then, we remeasured thee TF from F1 GAS excitation and it becomes healthy (fig1).
We are not sure the exact reason but one possibility is internal rubbing due to tilt of F1 body.
Anyway, we need to silghtly lower the setpoint of F1 GAS, which also requires to reconsider the setpoints of the other GAS filters to avoid changing the height of the mirror.
After Takahashi-san decided the new setpoints, I will remeasure the TFs again and continue health check.
I changed the setpoints for F1 and F3. I offloaded the F0, F1, and F3 keystones with the FRs.
| EY | count | um |
| F0 | 23100 | 4527 |
| F1 | -2754 | 1230 |
| F2 | 7000 | 1322 |
| F3 | -3561 | 1083 |
| BF | 825 | -700 |
After setting new GAS setpoints (klog21295), I remeasured TFs of GASs and BF.
Figure 1 to 3 are TFs of IP stage, Fig 4 to 8 are TFs of GAS filters, and Fig 9 to 14 are TFs of BF stage.
All TFs have no significant difference from the TFs measured before last evacuation (klog20729).
