Jenne, Evan, Nutsinee
We quickly repeated what Shiela had done in 2016 to see if we can see and reduce the scatter noise by injecting 0.1 Hz excitation to H1:SUS-ITM{X,Y}_R0_TEST_L_EXC. We were able to see scatter shelves with both CP X and Y excitaiton and we were able to improve the higher frequency shelve. However we ended up making some of the lower frequency shelve worse (ITMY CP Y=390 for example). Jenne thought that was unusual and worth alogging. More details and cleaner data to follow. We ended up at the gain of 400 for ITMX and 600 for ITMY. The slider bar were left at the place we thought the scattered noise was improved. That's PIT = 30 and YAW = 200 for ITMX CP and PIT=0 and Y=330 for ITMY CP. We didn't go very far in changing ITMY PIT slider bar. Something to revisit.
I tweaked these some more and arrived at the values (−300, −100) for the CPX offsets and (+300, −300) for the CPY offsets. I saw similar behavior to what Nutsinee said — moving CPY sometimes made the third-order shelf better but the second-order shelf worse, or vice versa. I finally found something that improved both, but we may want some more fine-tuned optimization of CPY.
For both CPs the relevant step size is about 100 μrad or so on the sliders, perhaps 20 μrad for fine tuning. Going much beyond ±300 μrad on the sliders will saturate the OSEMs.
Looks like Evan forgot to hit confirm on the SDF acceptance, but great news everyone! The guardian works as expected- at the lockloss we continued to return to "Check_SDF" until we figured out that we needed to confirm the changes. So all is well, these changes are confirmed and the SDF team has done their job well.
Around 2023-04-13 02:00:00 Z I drove SR3 up to 0.8 μm pkpk in length at 0.11 Hz, but could not make excess scattering appear in DARM. Approaching 1 μm pkpk caused a lockloss.
Around 2023-04-13 06:30:00 Z I drove OM1 up to 0.5 μm pkpk in length at 0.22 Hz, but could not make excess scattering appear in DARM.
Nutsinee's injections around 2023-04-10 22:20:00 Z amounted to about 15 μm pkpk length drive for CPX and 23 μm pkpk length drive for CPY.
Summary of these changes. The values after 10 April 2023 are currently used during O4.
| Offset | Before 10 April 2023 |
After 10 April 2023 |
|---|---|---|
| SUS-ITMX_R0_OPTICALIGN_P_OFFSET | 0 | −300 |
| SUS-ITMX_R0_OPTICALIGN_Y_OFFSET | +200 | −100 |
| SUS-ITMY_R0_OPTICALIGN_P_OFFSET | 0 | +300 |
| SUS-ITMY_R0_OPTICALIGN_Y_OFFSET | +170 | −300 |