A.Cosquer P.Keller on behalf of the KM3NeT consortium

1. Studies of an alternative glass pressure housing for optical modules in the KM3NeT neutrino telescope A.Cosquer P.Keller on behalf of the KM3NeT consortium VLVNT09 workshop Athens 12-15 october 2009

2. PLAN -Context - FEA studies - Integration aspects - Qualification Plans - Conclusion VLVNT09 workshop Athens 12-15 october 2009

3. 1 - Context A lattice of thousands of optical sensors will detect the Cherenkov light in the KM3NeT neutrino telescope The driving motivation for the “capsule” idea is to limit the cost of the neutrino telescope. One way to reach this objective is to reduce the cost of the pressure containers One basic idea is to limit the use of expensive material such as titanium or equivalent The other idea is to integrate as much as possible the PMTs with their dedicated electronics + associated storey equipment in the same container. VLVNT09 workshop Athens 12-15 october 2009

4. 1 - Context Backbone câble Backbone câble OF/Cu câble 6 Cu câbles 6 Cu câbles Cu câble OF/Cu câble • This solution will have other impacts on the global cost of the detector by reducing : • the number of mechanical supports • the number of holes/connectors and cables • the height of the structure line before deployment Comparative table for large PMs detector : Storey artist view VLVNT09 workshop Athens 12-15 october 2009

5. 2 - FEA Studies 2.1 Standard Glass Sphere 17 ” (Nautilus Data Sheet) • Geometry Caracteristic : • Outside Diameter : 432mm • Inside Diameter : 404mm • Thickness : 14mm • Inner chamfer : 1mm X 45 ° Mesh details • Material data : • Duran Vitrovex glass • Young’s modulus : 63 Gpa • Poisson’s ratio : 0.2 • Density : 2230 kg/mm3 • CPPM SCHOTT Calculation hypothesis : • Axisymmetric 2D model • Glasses are stress-free • Homogeneous material • (no surface default, no bubbles) • Hydrostatic pressure : 700 bars SCHOTT reference 14 mm CPPM – PATRAN/NASTRAN VLVNT09 workshop Athens 12-15 october 2009

6. 2 - FEA Studies For brittle materials : the calculation is done with ”maximal principal stress”(corner traction) and ”minimal principal stress”(global compression) Maximal principal stress : CPPM Patran Nastran study R&D SCHOTT study Max. tensile stress = 60 MPa  good correlation between both Minimal principal stress ROAK’s formula (analytical) a : Outside diameter b : Inside diameter q : hydrostatic pressure stress = - 576 MPa VLVNT09 workshop Athens 12-15 october 2009

7. 2 - FEA Studies 2.2 Standard Glass Sphere 13” (Nautilus Data Sheet) • Geometry Caracteristic : • Outside Diameter : 330 mm • Inside Diameter : 306 mm • Thickness : 12 mm • Inner chamfer : 1mm X 45 ° Maximal principal stress : • Material data : • Duran Vitrovex glass • Young’s modulus : 63 Gpa • Poisson’s ratio : 0.2 • Density : 2230 kg/mm3 • Calculation hypothesis : • Axisymmetric 2D model • Glasses are stress-free • Homogeneos material • (no surface default, no bubbles) • Hydrostatic pressure : 450 bars • (SCHOTT reference) CPPM – PATRAN/NASTRAN • Maximum principal stress ~ 31MPa (corner traction) • Minimum principal stress ~ - 330 Mpa (global compression) VLVNT09 workshop Athens 12-15 october 2009

8. 2 - FEA Studies 2.3 Design of a new ”capsule” glass First step : design and study made by the Nautilus Schott R&D department on a 10” capsule allowing to integrate two 8 ” PMs Next step : increase the capsule diameter to 11 ”for dimension constraints (volume for PM + connector + electronics) single glass piece OD : 279.40 mm ID : 247.40 mm Thickness : 16mm VLVNT09 workshop Athens 12-15 october 2009

9. 2 - FEA Studies Mesh details of interface : 23000 nodes FEA for 450 bars hydrostatic pressure : Maximal principal stress : (corner traction) CPPM – PATRAN/NASTRAN Minimal principal stress (global compression) 23 MPa -199 MPa 10 MPa -394 MPa VLVNT09 workshop Athens 12-15 october 2009

10. 2 - FEA Studies Good correlation with IFREMER studies Referring to the SCHOTT standard 13” spheres, the FEA results for the capsule glass pressure housing are very promising VLVNT09 workshop Athens 12-15 october 2009

11. 3 - Integration aspects External integration aspects: Wire straps • Hold the capsule in its frame Frame • Positioning (radial, axial, and rotation) the capsule • Fixing on the storey • Can allow backup with 2 glass 13”spheres Artist view Base • To maintain the rigidity between the capsule interface during deployment and transfer phase Internal integration aspects: • opticalgel thickness minimum • 8” PMs orientation between 20° and 25° to horizontalplane • available volume for the electronics boards will be at minimum 2. 103 cm3 • and a possible total surface of 900 cm2 VLVNT09 workshop Athens 12-15 october 2009

12. 4 - Qualification & test plans 24H stage 24H monitoring period 10 one hour cycles 1.2 Pimmersion … Patmospheric Following the IFREMER recommendations (NF XP X 10-800 / 31 SE05C for metallic containers), the preliminary qualification plan for the ”capsule ” : • Qualification plan on 30* preproduction units : • evaluation of the implosion pressure (rupture test) • 10 cycles to 1.2* x Pimmersion @ 12 bars/min followed by a 24H stage • acoustic (piezo sensor) and visual monitoring during the next 24 H (atmospheric pressure relaxation phenomena) * Coefficients for the pressure and unit numbers are under evaluationfor glassstructuresby IFREMER using a new custom reliability approach VLVNT09 workshop Athens 12-15 october 2009

13. 4 - Qualification plans 4 - Qualification & tests plan • Production plan (base on 10000 units): • 1 hour cycle to Pimmersion @ 12 bars/min on every 100th* unit • 1 qualification cycle on every 500th* unit (steps 2&3) • check of the implosion pressure (rupture test) on every 1000th* unit In the qualification phase, the hyperbaric tests could be associated with real deep sea immersion tests for full scale test and long term tests * Ratios are under evaluationfor glassstructuresby IFREMER using a reliability approach VLVNT09 workshop Athens 12-15 october 2009

14. 5 - Conclusion 5 - Conclusion .The FEA results for this new concept of deep sea housing look promising in comparison with standard sphere (reduced corner traction and global compression stress) . Consequently, the next step will be a qualification test as the necessary proof of feasibility of such a full glass container. . The cost reduction induced by such container could be interesting as well as the gain in reliability by reducing the number of holes/cables/connectors VLVNT09 workshop Athens 12-15 october 2009