[Aso, Tamaki, Tomaru, Yokozawa, Yasui, Ushiba]

Continued work from klog18902.

Abstract:
We centered the reflection beam from ETMX at IXC.
Then, realigning the reflection beam from ETMX to the GRX REFL PD by steering mirror after Faraday isolator.
After that, reflection beam from ITMX was centered to the GRX REFL PD and we found the GRX flashes.

Detail:
first, we tried to center the reflection beam from ETMX by using IX Tcam but found it is difficult because the reflection beam is not so strong.
Therefore, we decided to enter IXC and see the reflection beam directly.
To confirm the reflection beam position, we set aluminum cylinder in front of ITMX AR side (photo can be seen in the klog18916).
Then, we checked the beam position by monitoring IX Tcam (in this time, we can easily see the reflection beam because aluminum cylinder scattered the reflection beam).
Finally, we visually inspected the reflection beam position and confirmed that it hit the same position of injection beam.

After that, we noticed there are no reflection beam on GRX REFL PD, so we checked POP table.
The reflection beam reached FI but didn't hit PDs, so we aligned the beam to REFL PD.
Since the height of lens in front of REFL PD is too low and the beam hit the almost edge of the lens, we lifted up lens 9mm by inserting the spacers.
We also moved the iris, which was located after lens, to front of steering mirror because ghost beam hit lifted-up lens holder.
We also fixed some dumpers for dumping some ghost beam.

Then, ITMX alignment was done by using GR REFL PD as a reference.
First, I scaned ITMX pitch inclination by moving K1:VIS-ITMX_MN_TEST_P_OFFSET from -1000 cnts to 1000 cnts and see the GR REFL.
Since the middle of flat region of GR REFL signal is corresponding to 600-cnt offset, I set the OTIC ALIGN value to 600 cnts, which is corresponding to about 30 urad of OpLev signal.
After that, I tried to do the same measurent for yaw but before ding that we found the flash of GRX!!
So, I just read the PIT and YAW values when flashing and put them to the setpoint of angular control of ITMX.

After that, we started the scaning of I/ETMX best angles.
I injected the excitation signals to K1:VIS-{ITMX,ETMX}_MN_SET_{P,Y}_EXC to scan the mirror angles (detail configuration can be seen in fig2).
This scan will finish tomorrow morning (current highest peak is shown in fig 3).