KAGRA Logbook

Ushiba, Aso, R. Takahashi, Shimasue, Ikeda, Hirata, Akutsu; Ref: 16954.

Summary

Our objective is to finalize stuffs in IFI, IMM, and PRM chambers, which will be closed in the nex week. The finalization include main beam alignment and alignment relevant ghost beams to beam dumps. Today GRX path was confirmed. Alignmenf of the input IR beam axis to POP_FORWARD through PR2 and PRM is still on the way (we are at proceder #5 shown below).

Procedure planned

Refer to Fig. 1.

Release PRM, PR2, and PR3 as well as relevant suspended BB (breadboard). Note that an invac (to be invac) pick-off mirror (POP-POM) is on the suspended BB. POP-POM will reflect three beams: POP_FORWARD, GRX, POP (backward). GRX and POP should overlap in the nominal case.
Find GRX transmission at TMSX by sweeping PR3. Note that PR2 and PR3 should be at ALIGNED state.
Align the GRX spot on ITMX (not necessarily green flashing) to the "nice" location. The nice location should be the same one found during O4a. This align should be done with POP-POM.
Check GRX spot on PR2 and PR3. For PR2, if the spot would be too much shifted, the spot should be adjusted with a (in-air) steering mirror on the POP table. For PR3, the check is just for confirmation; we may not have any knobs to adjust this on PR3.
Inject IR from IMC; IO Guardian should be set "PROVIDING_STABLE_LIGHT" so that full IMC ASC should be kept. This mean the input beam axis to IMMT1T confirmed. Then do iteration with IMMT1 and IMMT2 to align beam pass through the center on PRM and a location on PR2; this location of PR2 should be, ideally, identical with the GRX path somehow determined above.
Then PR2 transmission, or POP_FORWARD, should be reflected by POP-POM and comes out of the PR2 chamber to POP table, so (if necessary) adjust the relevant periscope and following steering mirrors to introduce it to the POP_FORWARD QPDs.

Actual activities

After FC works (29254), PRM, PR2, PR3, and their BBs were released as planned. For PR3 release, as unfortunately as usual, PR3 was largely tilted and the oplev lost. The alignment was tentatively adjusted with picomotors. Fortutenately PR3 oplev came back, but one of the PR3 OSEMs would be about saturated. Because PR3 Guradian was able to reach ALIGNED, today we accepted this situation at this point. Later we need to adjust PR3 suspension manually.

Opening GRX shutter, and sweeping PR3, GRX transmission was immediately found at TMSX. The would mean that letting PR2 BB releasing/sitting might not so affect POP-POM alignment. This is good news. Also, the GRX spot at ITMX seemed almost the same as the one taken some days ago when the interferometer was nice alignment (the detail of this point will be separately reported by Ushiba-kun?)

Putting a PR2 HR target, we checked GRX spot on this target, and it was not so bad (mostly centerd but slightly shifted), so we left it as was. See Figs. 2 and 3. Then detaching the PR2 HR target, and putting a PR3 HR target, we also checked GRX spot on this target. As written in the above planned procedure, this was just for confirmation; we could not do anything on this spot (Figs. 4 and 5). By the way, when you would insert the target, the suspension should not be at ALIGNED state, as oplev and/or OSEMs might be affected by your beam cut or light illumination. If you are very much careful, you may be able to live with ALIGNED state, though.

Then we started iteration of the IR beam from IMC. As mentioned above, to IO Guardian, we called PROVIDING_STABLE_LIGHT, which means that the input beam axis is fixed to the sub-local area around IMC, and IMMT1T QPD was used as one of references. One should not cut the beam to IMMT1T to keep this alignment control. The iteration is: (1) check PR2 HR target and IR spot on it, and adjust the IR spot on it with IMMT2, (2) check PRM AR target and IR spot on it, and adjust the IR spot on it with IMMT1. (3) Repeat from (1) until the situation converges. But, for some reason, repeating several times, the situation was not so converged. Even more, before converging, for IMMT1 and IMMT2, the oplev range and/or coil actuator range both reached limits. We may start with taking care of these tomorrow morning.

Note

We may not need to do too much iteration, when looking at the current beam spot positions (Fig. 6; my iphone camera somehow can see a light spot on the target illuminated with 100 mW...)
Ushiba-kun suggested the other way later: illuminate almost center of IMMT2, then align IMMT2 to illuminate the nice position on PR2 target, then move PRM traverser so that the PRM target was nicely illuminated. This might be partly similar to way we had done in June 2021 (16954). If someone have other posts of initial alignment for finalization after June 2021, please let us know.
~~I should have used not PRM AR but PRM HR as this reference...?~~ -> It seems that PRM AR target was adjusted usable, according to 16954.
GRX beam spot on PR2 HR target will match with an IR beam reflected at PR2 but not with that of forward IR beam from IMMT2. In this sense, for example, GRX spot in Fig. 2 and IR spot in Fig. 4 should not match in yaw. See JGW-T2113078-v2.