ePIC pfRICH vessel & mirror design meeting

Tuesday 20 Jun 2023, 10:30 → 12:00 US/Eastern

zoom: https://bnl.zoomgov.com/j/1619779791?pwd=TUtVak9TMjdsb05CbkVrZmh2a2JzZz09

 

2023-06-20-pfRICH-VESSEL-DESIGN-MEETING

pfRICH vessel & mirror design meeting

 

06/20/2023

 

B. Azmoun, D. Cacace, J. Datta, K. Dehmelt, A. Eslinger, J. Esparza, P. Garg, A. Jung, A. Kiselev, W. Li, B. Moran, C.-J. Naim

 

The essential outcome:

• Replace cylindrical outer vessel profile by a dodecahedron matching the layout of the DIRC frame
• Confirm the intention to build mirrors in-house (substrates at Purdue, coating at Stony Brook)

Details:

1. Outer vessel wall. Given the fact that either a mandrel or a cylindrical mold would require a substantial investment, and DIRC support frame section is a 12-sided polygon rather than a circle anyway, there is no good reason to build the pfRICH vessel as a cylinder. A natural choice is to assemble the outer vessel surface out of twelve flat facets, ~35cm x ~50cm each. Each facet is a ½” thick honeycomb carbon fiber sandwich, with embedded carbon fiber reinforcement bars (either on two or all four sides). Bars can have a ½” x ½” cross-section. Embedding technique should most likely be a la Purdue (make a full size sandwich, mill out space for the bars, glue them in) rather than a la Stony Brook where bars would be glued in along with the sandwich construction (TBD). Threaded metal fixtures required for assembly will be embedded into the bars. Carbon fiber sheet thickness is yet to be decided (and hopefully can be ~10 mil like it was for the sPHENIX TPC).

• In a follow up conversation between AK and AE it was suggested that the twelve facets should be first assembled together using molded full size dodecahedron rings on the upstream and downstream ends, to have a rigid backbone to which the front and the rear plates will be mounted afterwards, rather than using these front and rear plates to bind the twelve facets together during the assembly

 

1. Inner wall. Present thinking is that this part can be molded out of a thin (~1mm or so) prepreg either as a single piece or perhaps consisting of two halves, with all the fixtures needed for mounting embedded into respective rims on the upstream and the downstream ends.

 

1. Front wall. The wall itself can be made as a single thin laminate disk (cured prepreg). Thickness (driven by structural stability) is to be defined. This disk will be bolted to the twelve facet dodecahedron assembly. The aerogel pockets can probably be 3D printed, have very narrow (<500 mm?) walls, and be attached to the front plate in a way to be defined later.   

 

1. Rear wall. Can be 3D printed as a single piece using reinforced graphite and will closely resemble the original aluminum plate design. Slots for HRPPDs (as well as other recesses if needed) will be machined afterwards. Dividers between the neighboring HRPPDs (1mm thick in the present design) will either need to be widened a bit or made partly low profile (both options possible and will be tried out in the first pfRICH prototype).

 

Honeycomb carbon fiber sandwiches will be produced by Stony Brook. The rest of the structure describe in items 1-4 will be built at Purdue.

 

 

 

1. Mirrors. A follow up meeting required. Discussion points so far: Two options considered for the substrates: (1) 3D printed, ~5mm thick, CNC machinable to achieve the required shape, (2) molded, perhaps ~2mm thick.

•  Both will require polishing to achieve an optical quality surface, unless one applies a ~10mil thick lexan film. In the latter case aluminum reflective layer and a MgF₂ (?) protective layer will be applied to the lexan film afterwards.
•  pfRICH mirror quality is less critical in the detector design as compared to dRICH (no focusing, not needed in the central portion of h acceptance).
• Stony Brook evaporator can handle pieces up to ~80cm size. pfRICH outer mirror segments will be ~50cm x ~50cm (assuming eight segments).

 

1. Prototype. Will be a full quadrant of the vessel (3 or 4 outer facets), with a single outer mirror segment, quarters of the front and rear plates, a fraction of the inner mirror cone, and a pair of flat walls to close the gas volume. The latter two can be made using whatever technique seems to be the easiest. All the rest will be designed and manufactured as a full chain prototype, using methods described in the previous sections.

 

1. Timelines. Stony Brook will confirm availability of the evaporator by the end of summer. Purdue will provide first small (flat?) mirror substrate samples, so that the in-house mirror coating trials can start early enough and guide the future process modifications.
2.