VLVNT09 workshop Athens 12-15 october 2009 1

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

Studies of an alternative glass pressure housing for optical modules

in the KM3NeT neutrino telescope

VLVNT09 workshop Athens 12-15 october 2009 2

- Context- FEA studies- Integration aspects- Qualification Plans- Conclusion

PLAN

VLVNT09 workshop Athens 12-15 october 2009 3

1 - Context

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.

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.

VLVNT09 workshop Athens 12-15 october 2009 4

1 - Context

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 :

Per storey Spheres 13”

(6+1)

Capsules 11”

(3 )

Holes nb 9 4

Cables nb 6 Cu

+ 1 OF/Cu

2 Cu

+ 1 OF/Cu

Mechanical support

7 3

Vacuum holes

7 3

Storey artist view

6 Cu câbles

Backbone câble

OF/Cu câble

6 Cu câbles

Backbone câble

OF/Cu câble

Cu câble

VLVNT09 workshop Athens 12-15 october 2009 5

2.1 Standard Glass Sphere 17 ” (Nautilus Data Sheet)

Geometry Caracteristic : •Outside Diameter : 432mm•Inside Diameter : 404mm •Thickness : 14mm•Inner chamfer : 1mm X 45 °

CPPM SCHOTT Calculation hypothesis :•Axisymmetric 2D model•Glasses are stress-free•Homogeneous material •(no surface default, no bubbles)

Hydrostatic pressure : 700 bars SCHOTT reference

Material data : •Duran Vitrovex glass•Young’s modulus : 63 Gpa•Poisson’s ratio : 0.2•Density : 2230 kg/mm3

Mesh details

CPPM – PATRAN/NASTRAN

2 - FEA Studies

14 mm

VLVNT09 workshop Athens 12-15 october 2009 6

For brittle materials : the calculation is done with ”maximal principal stress” (corner traction) and ”minimal principal stress” (global compression)

Minimal principal stressROAK’s formula

a : Outside diameterb : Inside diameter

q : hydrostatic pressure stress = - 576 MPa

Maximal principal stress :R&D SCHOTT study CPPM Patran Nastran study

2 - FEA Studies

good correlation between both

Max. tensile stress = 60 MPa

(analytical)

VLVNT09 workshop Athens 12-15 october 2009 7

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 °

Calculation hypothesis :•Axisymmetric 2D model•Glasses are stress-free•Homogeneos material •(no surface default, no bubbles)

Hydrostatic pressure : 450 bars (SCHOTT reference)

Material data : •Duran Vitrovex glass•Young’s modulus : 63 Gpa•Poisson’s ratio : 0.2•Density : 2230 kg/mm3

Maximum principal stress ~ 31MPa(corner traction)Minimum principal stress ~ - 330 Mpa

(global compression)

CPPM – PATRAN/NASTRAN

2 - FEA Studies

Maximal principal stress :

VLVNT09 workshop Athens 12-15 october 2009 8

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)

2 - FEA Studies

OD : 279.40 mmID : 247.40 mmThickness : 16mm

single glass piece

VLVNT09 workshop Athens 12-15 october 2009 9

Mesh details of interface : 23000 nodes

FEA for 450 bars hydrostatic pressure :

2 - FEA Studies

Maximal principal stress :(corner traction)

Minimal principal stress(global compression)

CPPM – PATRAN/NASTRAN

23 MPa

10 MPa

-394 MPa

-199 MPa

VLVNT09 workshop Athens 12-15 october 2009 10

Maximal principal stress (corner traction)

Minimal principal stress

(global compression)

Glass sphere 17 ”

P = 700 bars 60 MPa - 576 Mpa

Glass sphere 13 ”

P= 450 bars 31 Mpa - 330 Mpa

New capsule 11 ”

P= 450 bars23 Mpa Cylinder : -395 Mpa

Hemisphere : -199 Mpa

2 - FEA Studies

Referring to the SCHOTT standard 13” spheres, the FEA results for the capsule glass pressure housing are very promising

Good correlation with IFREMER studies

VLVNT09 workshop Athens 12-15 october 2009 11

• To maintain the rigidity between the capsule interface during deployment and transfer phase

• Positioning (radial, axial, and rotation) the capsule• Fixing on the storey• Can allow backup with 2 glass 13” spheres

Wire straps

Frame

Base

3 - Integration aspects

• optical gel thickness minimum• 8” PMs orientation between 20° and 25° to horizontal plane• available volume for the electronics boards will be at minimum 2. 103 cm3

and a possible total surface of 900 cm2

Internal integration aspects:

External integration aspects:

• Hold the capsule in its frame

Artist view

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4 - Qualification & test plans

Following the IFREMER recommendations (NF XP X 10-800 / 31 SE05C for metallic containers), the preliminary qualification plan for the ” capsule ”   :

* Coefficients for the pressure and unit numbers are under evaluation for glass structures by IFREMER using a new custom reliability approach

Qualification plan on 30* preproduction units :

1. evaluation of the implosion pressure (rupture test)

2. 10 cycles to 1.2* x Pimmersion @ 12 bars/min followed by a 24H stage

3. acoustic (piezo sensor) and visual monitoring during the next 24 H (atmospheric pressure relaxation phenomena)

1.2 Pimmersion

Patmospheric…

24H stage 24H monitoring period10 one hour cycles

VLVNT09 workshop Athens 12-15 october 2009 13

4 - Qualification plans 4 - Qualification & tests plan

Production plan (base on 10000 units):

1. 1 hour cycle to Pimmersion @ 12 bars/min on every 100th* unit

2. 1 qualification cycle on every 500th* unit (steps 2&3)

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 evaluation for glass structures by IFREMER using a reliability approach

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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