Coming out of the latest collaboration meeting, and after some discussion in Valencia, a revised picture of the pressure vessel has emerged. There is more uncertainty, than first thought, regarding the technology and design of the PMT, and SiPM, EL, and HV systems. In addition, our goal is to move the pressure vessel design forward, with a final design sometime in Fall, that we can proceed with fabrication. So the idea is to decouple the pressure vessel as much as possible from the internals and simplify its design to a one-size-fits-all vessel. PMT's will live inside the vessel, either hardened, or encapsulated.  Unused volume inside the vessel will be filled with radiopure plastic, such as polythylene, that is copper plated in order to avoid Xenon diffusion. The pressure vessel is currently scheduled to be fabricated from pure titanium, ASTM grade 3 (or 2)pending verification of acceptable radiopurity.

The pressure vessel design, fabrication and certification will be done to ASME pressure vessel Code, section VIII division 2, as much as is possible. Any exceptions must be fully reviewed and approved by an appropriate technical committee.

The vessel fabrication process is as follows:

1. We write a Specification for the Vessel which includes all dimensions, media, conditions, loads, etc. that the vessel will be subject to. We will add additional conditions that allow us to assure quality in particular, for radiopurity, from material purchase, through all cleaning, joint preparation, welding, pressure testing step. 

2. This specification must be certified by an independent certification authority to assure that the vessel is fully specified. 

3. A certified Inspector must be hired to inspect all stages of the fabrication and certify the vessel is being built in accordance with Specification; we will also perform our own inspection of the fabrication process. 

3. The fabricator must be certified to perform all the operations specified in the Specification. They must have a certified Quality Assurance Program in place that can track progress and demonstrate compliance

VESSEL DESCRIPTION:

POSSIBLE EXPERIMENTAL CONFIGURATIONS:
  Asymmetric:  
    Energy plane at cathode:
	1. 36-60 encapsulated 3" DIA PMT's -4 pins each, max
	2. 240 (max) hardened 1" cube PMT's - 4 pins each, max
    Tracking plane, at anode:
	1. 180-200 SiPM DB's (64/DB) - 1 coax (2 pins), 1 optical fiber each
	2. 240 (max) hardened 1" cube PMT's - 4 pins each max
  Symmetric:
    Energy/tracking both ends:
	1. 240 (max) hardened 1" cube PMT's both ends, ~70 kV central HV mesh with feedthrough port


	

	
	
CURRENT ENGINEERING ISSUES WITH THE PRESSURE VESSEL DESIGN:

1. Lack of suitable bolting material- ASME code is particularly stringent here -no high strength radiopure material allowed; no Ti bolts - we a need material exception; preliminary calcs show that simply designing for huge copper (or Si bronze?) bolts results in huge flanges (25 cm thk, 1.9m OD). Any hope for radiopure Inconel 718? (50% Ni,20% Fe,20%Cr, with several percent Mo, Nb, 1% Co), high strength steel? should we test? (I'll check Al's database)- A better suggestion, from Sara, is to use a two-piece clamped joint. These are more efficient, allow radiopure materials for the clamps, will have a smaller OD (except at clamp ends, which can be located in the corners of a lead castle) and greatly ease assembly/dissassembly. Win-win-win-win! A Ti anodize process will need to be aplied to the clamps to avoid galling.
2. Flanges and clamps may not be machined from plate using div. 2 rules. This is likely due to planar imperfections in the rolling direction being cross wise to the high stress direction. We will need (roll or other) forgings made, or roll and weld very thick plate