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MICE Meeting9/26/2003

Absorber design updateEdgar L. Black

IIT

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NON-WELDED WINDOW CURRENT DESIGN

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SOLID ABSORBER CHANGE OVER CONCEPT

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THE ALUMINUM WINDOWS ARE REMOVED FROM THE NON WELDED ASSEMBLY AND PRE MACHINED COMPONENTS ARE INSTALLED FOR THE TEST OF THE SOLID ABSORBER

• ON THIS CONFIGURATION, THE SOLID ABSORBER IS COMPLETELY EXPOSED TO THE BEAM PATH; THEREFORE, DATA COLLECTED WILL BE FREE FROM THE SCATERING PRODUCED BY THE ALUMINUM WINDOWS

• THE ABSORBER HEAT EXCHANGER IS ISOLATED BY A CYLINDRICAL INSERT AND A SEAL CUP

• THE INSERT CAN BE FABRICATED WITH INTEGRAL FIXED SUPPORTS FOR A PARTICULAR ABSORBER MEDIA OR

• SEPARATE RING INSERT-BRAKETS SUPPORT THE ABSORBER AT LOCATIONS TO MEASURE THE ABSORBER EFFECT AT VARIOUS POSSITIONS WITHIN THE MAGNET FIELD

• ADDITIONAL SEALED RING-CAPS ISOLATE THE VACUUM CHAMBER TO PREVENT POTENTIAL CONTAMINANTS INTO THE VACUUM SYSTEM

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ALTERNATE CONFIGURATION THE VACUUM WINDOWS ISOLATES THE ABSORBER FORM THE MICE VACUUM

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PURPOSE OF ALTERNATE DESIG CONFIGURATIONS

• Condition may exist when the absorber material is susceptible to non desirable contamination from MICE or vice versa.

• The absorber vacuum system on this case will be isolated and designed for ease in decontamination, including disposable system elements.

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SEALS SELECTION CONSIDERATIONS•The Absorber vacuum chamber is expected to operate between 50 to 70 K temperature the chamber can be constructed from 304 stainless steel on its entirety for its low thermal conductivity and strength for handling it during the change over operations; the design of the seal to the 6061-T6 aluminum window becomes simpler and les expensive.

From a reference on “Practical Vacuum Techniques” By William F. Brunner, Jr. and Thomas H. Batzer. Lawrence Radiation Laboratory Livermore, California (1,965)

• Aluminum-foil (or other material foil) flange seals are cheap and reliable, the mating flanges are symmetrical and the least expensive to make. These seals remain leak –tight from liquid nitrogen temperatures to bake out temperatures of 400 K (a temperature excursion of 600 K)

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Conceptual design for cryogenic seal between flanges of dissimilar material

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PRINCIPLE OF OPERATION

The aluminum-foil flange seal owes its ability to withstand thermal cycling and dissimilar expansion coefficients of the material to its flange design as shown above.The flanges seal faces are machined at a small angle: as the flanges are tightened together the flanges bend, until the opposing flanges seal faces are very nearly parallel. The aluminum gasket is then under a large load, and considerable work energy is stored in the rotated flanges. This stored energy prevents flange-unloading do to thermal changes.

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PRELIMINARY CALCULATIONS

The following equations are good approximation of the maximum stress and the rotational deflection due to the load Fb and the gasket reaction FG:

  smax = MR/Z (1) F = MR2/EI (2)where 

M = Fb X b/2 = moment in lb-in. per inchR = radius in inches to flange cross-section centroid,Z = bd2/6 = flange section modulus in in.3

I = bd3/12 = moment of inertia of the flange section normal to flange

Es = modulus of elasticity (28 X 106 psi for 304 stainless steel)

EA= modulus of elasticity (10 X 106 psi for 6061 Aluminum)

  

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Substituting into Eq. (1),

  smax = 3FbR/d2 psi (3)

Substituting into Eq. (2),

F = 6FbR/Ed3 radians (4)

Combining Eqs. (3) and (4) and changing to degrees

F = 4.09 X 10-16 smax R/D degrees (5)

 

Fb = 2,480 lb, d = 1.125 in., d2 = 1.268 in2, R/d = 6.11, R/d2 = 5.42,

smax = 40,300 psi, calculated F=1.01 deg. Actual = 2 deg.+/-10’

 

 

PRELIMINARY CALCULATIONS CONTINUED

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AlSS

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WELDED WINDOW DESIGN

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WELDED DESIGN CAPABILITY COMPARISON

•Requires R&D to test performance of seal welds at cryo temperatures. The machined tolerance for the shear force restriction on the weld needs test for assembly and for performance•Requires a tool to handle and protect the windows at assembly •Has limited reusability do to the metal structural modification produced by the welding process.•Not readily adaptable for solid absorber tests, requires dedicated assembly configurations for each absorber material and type of test•Assemblies with dissimilar material are not permitted e.g. SS and Al•Requires longer period of shop time (down test time) for change over or repair unless a complete new stand-by-assembly for each experiment is available•Approximate cost per base assembly $ 20,000 •Cost for 12 change over operations $ 240,000 for 3 units and for the live of the experiment (W. Lau estimate) •R&D welding development in prototypes + cryo auxiliaries $25,000

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NON-WELDED DESIGN CAPABILITY COMPARISON

•Requires R&D to test performance of gasket seals at cryo temperatures•Requires a tool to handle and protect the windows at assembly and disassembly•One absorber assembly is adaptable for all liquid and solid absorber media tests•The design can accommodate dissimilar materials between aluminum windows and 304 SS absorber vacuum chamber•Accessibility through removable windows allows prompt recuperation if a non acceptable leak rate is detected•Approximate cost for the base assembly (one time only) $ 22,800 •Cost for change over varies per experiment, average/unit $ 3,000 •Total for the live of the experiment assuming 12 change over operations and for the 3 units $ 176,400•R&D Seals and flanges development with prototypes $21,000

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CONCLUSIONS• The design details are preliminary at this

stage considering the nature of their objective and shall be taken as such for budgetary an scheduling purposes only.

• It is imperative that both welded and non-welded will have a R&D program geared to prove a safety compliance with the physics criterion before selection.

• A final evaluation should be based on the physics experiment criterion