Summary
The last remaining beam dump for ghost beams coming back from the REFL window into vacuum has been installed.
Details
After Mirapro staffs have done sealing the K400 flange in the minus Y of IFI chamber (22241) that had been detached last year (16689), the first thing I did was to tentatively attach the high-qualty super-expensive viewport window (Cat.A; JGW-D1402644) on the K400 flange. The window has a wedge of 0.75 deg, and thicker side should come in the minus X direction; see page 20 of JGW-T1504233 (although in this document, the beam dump is of type for S-pol, but actually the beam around here is P-pol, so the beam dump really used is also for P-pol today).
To check where the REFL beam arrived, I called IMC_LSC_LOCKED, and also aligned PRM by calling ALIGNED so that the IR reflection beam from PRM properly arrived at the IFO_REFL. In my eye-balles, the beam was not out of the first periscope on the REFL table, and maybe thanks to the proper lens focusing, the beam seemed entering the RFPD(s) well. Also, the DC readout of this RFPD seemed not so bad when looking back the same readout channel in this morning when the cavities were aligned by Ushiba-kun(?). But please check later.
Then I moved the beam dump to the position where it could catch the two ghost beams back to the inside of the IFI chamber from this window (Fig. 1). To see the beam positions, I attached a sensor card on a tip of a dentist mirror with taping roughly, and inserted it through another ICF152 viewport labeled as C-2-6; actually I newly opened this C-2-6 viewport for this purpose today.
Monirtoring the IMMT1T QPDs and POP_Forward QPDs, I careflly tightened the clamp for the beam dump foot. The C-2-6 viewport window was also used to access the clamp screws. Finally I applied torque on all the screws for the viewport window in the usual manner; ICF152; 5 -> 10 -> 15 Nm (Figs. 2 and 3).
Note
The ghost beams going back to the IFI chamber were caught by my work today, but note that the other one, the ghost beam coming out of the chamber accompanying the main REFL beam has to be dealed with by commissioners later on the REFL table properly.
