[Uchiyama, Dan, Washimi, Yokozawa, Ushiba]

Abstract:

We set two irises: one is in front of IFI and the other is in front of IMMT1.

Detail:

Preparation:

Before starting to set irises, I performed alignment in the following procedure.
1. IMC was locked with ASC.
2. POP FORWARD QPDs are aligned to the good values with IMMT1 and IMMT2.
Since we know that GV closure does not affect so much to the beam spot on QPDs (klog29448), it should be one of the best efforts to recover the good alignment when PRFPMI was locked.
Figure 1 shows the QPD signals after the alignment (Y cursors show the good values when PRFPMI was locked).

After that, IMMT2 OpLev was centered because IMMT2 OpLev signals was jumped during the vacuum opening work and old good value was no more good.
Currently, actuator feedback was very large, so it should be offload at some point.

Setting iris in front of the IFI:

After alignment was recovered, I set the iris in front of the IFI (fig2).
Centering of the iris was done so that the scattered light around the iris center hole ibecomes isotropic (fig3).
Due to the KG5 glass behind the IFI, it is hard set it more close to IFI but I hope this position doesn't conflict the STM2 work.
Iris was fixed with M6 screws while we were confirming there was no change at IMMT1T QPD signals.

Setting iris in front of IMMT1:

To avoid clipping the IMMt1 reflection by the iris, I set the iris slightly far from the IMMT1 (fig4).
At that position, IMMT1 reflection beam doesn't seem to be clipped (fig5, it is hard to identify it from this figure, though).
We tried to check the centering of the iris in the same manner as the iris in front of the IFI but found that it was difficult because some ghost beams hit on the iris and it was difficult to identify the main beam.
So, we aligned the iris with the following procedure.
1. Close iris until the hole becomes slightly smaller than the beam size.
2. Move iris horizontally to maximize the SUM of IMMT1T QPD and fixed it.
3. Change the height of iris to maximize the SUM of IMMT1 QPD and fixed it.
Though the precision of the centering is not excellent, it should work for the target to lead the beam on IMMT1T QPDs (if the beam passed the center of ithe ris, the beam also hit on IMMT1T QPDs).
So it should be enough for our purpose.