[Kambara, Furuhata, Okutomi, Shoda, Kuwahara, Ushiba, Uchiyama, Michimura]
We have done the initial alignment of the beam into IXA (great work, team!).
The measured beam radius at PR3 was
wx = 35.3 +/- 0.2 mm
wy = 37.5 +/- 0.3 mm (designed value: 36.8 mm)
What we did:
1. Measured the beam profile of the beam from PR2, at the position between PR3 and PR3-PR3 duct. The result was attached. The profile looks quite nice, and the measured beam radius was consistent with the designed value, since the systematic error of the measured value is 8 %, according to the vendor (info from Moriwaki-san).
2. Re-centered the beam on PR3 by adjusting PR2 alignment by hand.
3. Tried to center the beam on BS by adjusting PR3 alignment with the traverser and the picomotor on IM. We could center the beam in yaw, but the beam height was too high (~10 cm higher than the center of the BS). It seemed out of adjustment range of PR3 (which turned out to be false).
4. Re-measured the beam height and the optic height with laser marking devices at BS and PR3, and fine-adjusted PR2 alignment.
5. Tried again to center the beam on BS, and we succeed.
6. Opened the IXA chamber and confirmed that the beam is there. The beam was not at the center of the chamber, but rather at AS side. Also, the beam seemed to be clipped (attahed photo). It might be from the BS, since it's clear aperture is 74 mm dia (45 deg incident).
7. We will left the Koach filters at PR3 and PR2-BS on, with flanges opened. We will also left the beam (~250 mW) on until Sunday.
Next:
1. Sweep PR3 and wait for EXA PD to get any signal
2. Beam profiling at IXA (if we don't see any signal)
I don't know how many times I should say this but it would be nice to increase the exposure time of the beam profiling software...
About the "clipped" beam profile: did you check whether the beam is hitting once or twice the duct in-between the PR3 and PR2 chamber??
I forgot to mention that one of the three vertical OSEMs on IM for PR3 was out of range after this alignment (which seems strange). We might have to re-adjust the OSEM position.
We centered the TM oplev after the alignment, so we can use the oplev for alignment reference.
Is it just an issue of relative position of the flag and the sensor part? Does "out-of-range" mean the output is zero or max, which??? In the "zero" case, there is a possibility that the OSEM's fragile circuit would be again broken.
And, don't forget that the cryo-duct shields are existing at each side of the IXC. The opening apertures of the both duct shields could be less than your imagination, and also they have baffles. Looking over the younger workers' names, I'm afraid none of you would be familiar with the cryo-duct shields... if so, please talk with Kimura-san there.