KAGRA Logbook

Aso, Yokozawa, Akutsu; following 28827.

Summary

We have tweaked the GRY green beam spot on the centers of SR2 and SR3.

Details

As reported in 28827, each green beam spot on SR2 or SR3 off-centered. So we started with checking if PZTs attached on the steering mirrors on the POS table would be ok by simply looking at their drivers' displays, and seemed ok; two pzt driver units showed around 75 V in the display (Fig. 1). Note that in our experience, even though the PZT would be broken, mis-alignment of GRY beam line would be not so large.

Then we connected tentatively the pitch/yaw picomotors on POS-POM (the in-vac steering mirror on the suspended table in the SR2 chamber) to the existing pico driver. Looking at the green beam spot on a beam target at SR3 HR, we tweaked POS-POM with the picomotors via MEDM. The green beam spot on SR2 was also checked with a beam target set at its HR side (not AR side), and this mis-centering was adjusted by tweaking the final mirror in the air i.e. the upper mirror on the periscope on the POS table. We iterated this procedure some time, and confirmed that the beam spots on SR3 (Fig. 2) and SR2 (Figs. 3 and 4) seemd (on the relevant targets) centered.

We detached an aluminum cover in-between SR2-BS and a tentative tube was made by aluminum foil, so you can do GRY search.

Note

As mentioned above, POS-POM and "the upper mirror on the periscope" were tweaked, so later the IR beam through SR2 to the POS table might be shifted, and so the following beam paths to the relevant gige camera and/or PD should be also adjusted.
It would be nice to change the lables on the pzt drivers from the old names to the relevant newer ones (see Fig. 1; currently, two driver units of the bottom one labeled with "ALS-Y STM2" "POS GrM3" but the labels would not be true anymore).
The green beam spots are: maybe slightly higher at SR2 HR?; And maybe slightly lower at SR3 HR? (if the most brightest area in Fig. 2 would be the beam center). But note that the target plates would have also some errors, so it would be better to try GRY search.