Ans Pardons 30/11/2006CNGS Reflector Technical Review CNGS reflector: Status Work remains to be done… 30/10 Introduction Drain connection Event analysis Guidelines for new design

Ans Pardons 30/11/2006CNGS Reflector Technical Review Introduction (1/1) Water flow: 50 l/min No pressure, flow by gravity Estimated 18 l/min in last (red) connection Reflector layout sprayers drain tube (behind frame)

Ans Pardons 30/11/2006CNGS Reflector Technical Review Drain connection (1/4) Evacuate water from outer conductor to drain tube Connection between different polarities (500V) 5 identical assemblies in reflector, idem for horn

Ans Pardons 30/11/2006CNGS Reflector Technical Review Drain connection (2/4) Installed on horn & reflector Ceramic for electrical insulation Brazing, seals and collars to ensure leak & vapor tightness Bellows to give (some) flexibility Overlap (2x1.5cm) to ensure leak tightness if seal corrodes  Compressing bellows (max 2cm) does not suffice for dismounting or installation of the piece Picture taken in assembly lab Cross section

Ans Pardons 30/11/2006CNGS Reflector Technical Review Drain connection (3/4) Brazing Titanium flanges carefully machined Ceramic machined for precise fit (but introduces stress concentration) Ceramic = alumina type AL300 (97,6 %) with MoMn and Ni deposit Brazing through AgCuPd and AgCu Thickness of flange reduced to minimize residual stresses in ceramic Titanium flange Ceramic (machined) (info and picture from S. Mathot)

Ans Pardons 30/11/2006CNGS Reflector Technical Review Drain connection (4/4) Observations: Ceramic broken over full section Gap of ~1mm Leak of 15% of flow Misalignment visible? Work remains to be done… Ceramic Titanium

Ans Pardons 30/11/2006CNGS Reflector Technical Review Event Analysis (1/4) Ceramic Titanium Reasons for stress/rupture of ceramic : Brazing Machining of ceramics Thermal cool down after brazing Alignment errors Pile up of tolerances Error during assembly Additionally, the geometry is very rigid: Collars for vapor tightness (seal) Insufficient flexibility of the bellows (Vibration) Accident during assembly?

Ans Pardons 30/11/2006CNGS Reflector Technical Review Event Analysis (2/4) Ceramic Titanium Brazing Machining of ceramics Stress concentration at “shoulder” Stress value unknown (tension & compression) Thermal cool down after brazing With thick flange (first design) Broken ceramic observed after cool down Stress estimated at 280 MPa With thin flange (final design, installed) Stress estimated at 190 MPa (mainly compr.) Material data of Al2O3 Yield strength (tension): ~300MPa Yield strength (compression): ~2000MPa Young modulus: 300GPa Shear modulus 150GPa Ceramic Titanium

Ans Pardons 30/11/2006CNGS Reflector Technical Review Event Analysis (3/4) Alignment errors - Rigid assembly Stainless steel collars leave no flexibility, alignment errors are transmitted as stress to the ceramic Space constraints limit the length of the bellows. The bellows is not sufficiently flexible to absorb alignment errors larger than 1mm Different types of alignment errors Displacement error vs Parallelism error (assume flexible bellows) Flange Ceramic Flange Ceramic Bellows Flange Ceramic Collar Bellows Flange Ceramic Collar

Ans Pardons 30/11/2006CNGS Reflector Technical Review Event Analysis (4/4) (Vibration) Extrapolation from vibration measurements: Displacement of drain connector estimated <0.1mm Unlikely to have contributed to failure Conclusion Failure due to sum of stresses from alignment errors and brazing procedure. Live to learn Guidelines for new design

Ans Pardons 30/11/2006CNGS Reflector Technical Review Guidelines new design (1/1) No brazing or machining of ceramic Ensure complete water tightness Ensure a certain level of vapor tightness Minimize effect of alignment errors Foresee gaps to absorb alignment errors Foresee flexible parts or soft materials Careful assembly Geometrical inspection before installation Proposal for new design Stephane’s Talk