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

Ans Pardons30/11/2006 CNGS Reflector Technical Review

CNGS reflector: StatusCNGS reflector: Status

Work remains to be done…30/10

Introduction

Drain connection

Event analysis

Guidelines for new design


Introduction (1/1)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)


Drain connection (1/4)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



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



BrazingTitanium 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)



Observations:Ceramic broken over full sectionGap of ~1mmLeak of 15% of flowMisalignment visible?

Work remains to be done…

Ceramic

Titanium


Event Analysis (1/4)Event Analysis (1/4)

Ceramic

TitaniumReasons for stress/rupture of ceramic :Brazing

Machining of ceramicsThermal cool down after brazing

Alignment errorsPile up of tolerancesError during assembly

Additionally, the geometry is very rigid:Collars for vapor tightness (seal)Insufficient flexibility of the bellows

(Vibration)Accident during assembly?



Ceramic

Titanium

BrazingMachining 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 downStress estimated at 280 MPa

With thin flange (final design, installed)Stress estimated at 190 MPa (mainly compr.)

Material data of Al2O3Yield strength (tension): ~300MPa

Yield strength (compression): ~2000MPaYoung modulus: 300GPaShear modulus 150GPa

Ceramic

Titanium



Alignment errors - Rigid assemblyStainless steel collars leave no flexibility, alignment errors are transmitted as stress to the ceramicSpace constraints limit the length of the bellows. The bellows is not sufficiently flexible to absorb alignment errors larger than 1mm

Different types of alignment errorsDisplacement error vs Parallelism error

(assume flexible bellows)

Flange

Ceramic

Flange

Ceramic

Bellows

Flange

Ceramic

Collar

Bellows

Bellows Bellows

Flange

Ceramic

Collar



(Vibration)Extrapolation from vibration measurements:Displacement of drain connector estimated <0.1mmUnlikely to have contributed to failure

ConclusionFailure due to sum of stresses from alignment

errors and brazing procedure.

Live to learn Guidelines for new design


Guidelines new design (1/1)Guidelines new design (1/1)

No brazing or machining of ceramicEnsure complete water tightness Ensure a certain level of vapor tightness

Minimize effect of alignment errorsForesee gaps to absorb alignment errorsForesee flexible parts or soft materials Careful assemblyGeometrical inspection before installation

Proposal for new design Stephane’sTalk

Documents

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