ePIC pfRICH mechanical design mailing list

["Kiselev, Alexander" <ayk AT bnl.gov>]

  Hello colleagues,

  our present shim design (a 1mm thick spacer between HRPPD and the readout board) looks like the first attached model, and is only good to align the compression interposers.

  When re-designing the HRPPD enclosure for the test stand, I realized that it can be slightly modified, and also be used to provide light tightness to the setup.

  But then it occurred to me that a similar trick can probably be used when mounting HRPPD into the pfRICH sensor plate, see the second file attached, where the purple part is a shim, and the green part is a readout board. Such a "functional shim" (a pocket):

  (1) hides the uncertainty related to the HRPPD shape (we would ship it to Incom, and it is then their task to make sure that produced tiles fit, either loose or tight, yet without a deformation; then we are dealing with a perfect ~121mm square shape which can be packed tight into the sensor plate)

  (2) almost certainly provides a sufficient light tightness, even if we do not tape the cracks between the pockets on the rear side of the sensor plate (but we probably should anyway)

  (3) covers the otherwise exposed indium seal, and therefore resolves the electrical safety issue

  Looking at this model, I'd say we can then simply glue 1/8" threaded rods into the ~7mm x 7mm (or whatever is left) square spots between the tiles, at least for the prototyping phase, and use either large nuts or large washers to fix the sensors. Sensors are then not independent when we mount them, but we should probably reconsider this requirement anyway. I suspect we will never be able to replace an HRPPD in situ in the experiment. The cooling system pipes need to be dismounted anyway. So what's the point?

 Gas tightness problem perhaps also needs to be reconsidered a bit. In this approach, a thick enough soft flat gasket would pretty much work I suspect. One can also think how to better tape the cracks between pockets, making the whole rear surface gas tight. And if at the end a purified nitrogen leaks into the hall, who cares?

  Anyway, omitting a gas tightness issue to start with, can we develop this into a working option? The attached model is merely a concept. I did not pay much attention to the sizes, although they are reasonably close to the actual ones.

  Cheers,

     Alexander.

  

Attachment: shim-2023-11-25.stp
Description: shim-2023-11-25.stp

Attachment: more-than-just-a-shim.stp
Description: more-than-just-a-shim.stp