Isaac Earle has recently been managing the fabrication of some new Be target cassettes for the T1 / T2 Meson Hall target ladders (WO 41527).

The machine shop has outsourced the cassette tubes to an external shop for wire EDM cutting, as it produces a much more repeatable and consistent wall thickness without the need for delicate forming and welding.

However, the legacy end-cap design TBP1690 calls out a thin-wall formed frame to help brace the window in place and provide material to fusion weld the rim of the end cap to the cassette tube.  The legacy design frame is extremely thin compared to the tube wall thickness, and this mismatch is extremely difficult to EB weld reliably.  If a mistake is made, the entire EDM cassette tube is scrapped.

Bob Welbourn and the machine shop have come up with an improved design for the frame and window with slightly modified forming tools.

The window thickness .003" and tube wall thickness .010" remain the same.  The only change is to the thickness of the welding frame, which is now matched with the tube wall thickness (previously .003", now .010").

Photos of the old (right) and new (left) weld results are attached, as well as the new forming tools created by Bob Welbourn.

The shop is now able to make a confident and reliable weld for the end caps.

I am not sure that the increased frame thickness will have any affect on the beam entry into the target cassette, but my assumption is that this region is not critical.  Now, if the beam does enter that material at the edge of the cap / tube, and the temperature changes during operation, there will be a more secure weld there due to this design improvement.

The machine shop was waiting for the OK to finish welding the end caps into the frames using this new technique / design, and seeing as how the old option was likely to produce more leaking or scrap parts, I gave them the go-ahead to proceed.

Isaac will take care of the drawing and documentation updates when he returns from holiday.

Thanks and regards,

Grant