Hirata, Akutsu on 26 Apr 2024; following 29342.
Summary
Checked if ghost beams were within the relevant beam dumps in IMM chamber.
Setup
The same as 29342 basically. Plus, request IMMT1 Guardian to PAY_FLOAT, as we need to check behind IMMT1 and cut/shut the oplev beams.
Details
For the reference drawing, see Fig. 1 of 21578 (finalization in 2022); but I think we would need the newer version of this...
Behind IMMT1
Behind IMMT1, there are a pick off mirror (IMMT1T-POM) and a beam dump, while there are four transmission beams:
- Forward IMMT1 transmission. Most of this is reflected by IMMT1T-POM within the chamber, and becomes ISS beam. A part of this, or transmission of IMMT1T-POM is used as IMMT1T beam for IMC-ASC.
- Backward IMMT1 transmission. Most of this is reflected by IMMT1T-POM as well, but to be dumped later within the chamber (shown later). A part of this would trasnmit out of the chamber throught a viewport, and should be around IMMT1T beam; hopefully properly dumped on the in-air optical bench.
- IMMT1 AR reflection (forward); this is an IMMT1 AR reflection of "1" above. To be dumped here.
- IMMT1 AR reflection (backward); this is an IMMT1 AR reflection of "2" above. To be dumped here.
Fig. 1 shows the beam "1" and "2" mentioned above are within the IMMT1T-POM (pick off mirror). Fig. 2 shows the ghost beams "3" and "4" mentioned above are within the beam dump.
Backward beam through IMMT1 and reflected by IMMT1T-POM
Fig. 3 shows the beam "2" mentioned above is dumped by the relevant beam dump. Due to the mirror-like surface of the structure, a vertual image of the sensor card and the ghost beam can be also seen; please not confused if there might be two ghost beams; it seems only one GB.
ISS beam reflected at the relevant viewport window
Fig. 4 shows a (actually two degenrated) ghost beam generated at a viewport window through which a beam for ISS passes. In theory there should be two ghost beams, but due to the narrow separation of the two beams, they can be caught with a single beam dump.
Note
- The other beam dumps and shields were already checked the other day. For example, see Fig. 8 of Day 6 (29334).
- Different from IFI chamber, IMM chamber is not so shining when I saw it with IR camera. By the way, interestingly, Fig. 5 shows something above PRM is shining in IR. Fig. 6 was taken after Fig. 5, and maybe these are from OSEMs. Even when we shut the PSL IR beam, these IR still there.
- For accessibility, we newly detached a blank flange D-2-4 of IMM chamber (Fig. 7)
