Hybrid Structure with Cooling

John Cozzolino

LARP Collaboration MeetingPort Jefferson, NY

November 4-6, 2009

Outline

• Basic Design Features• 2-D Magnetic Analysis

– Compute Lorentz forces in coil at 200 T/m flux gradient

• 2-D Mechanical Analyses– Determine maximum coil azimuthal pre-stress sustained by collar– Study stresses and deflections during assembly and operation

• Determine necessary bladder pressure and yoke shim sizes• Check critical gaps, clearances and stops, as well as coil and shell stresses• Note spring-back loss of coil stress after yoke shim installation• Note cool-down effects on coil stress and shell stress• Check coil pre-stress loss at pole due to Lorentz forces during full power• Determine coil mid-plane horizontal deflection from 0 -> 200 T/m

• Conclusions• Recommendations and Remaining Tasks

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Basic Design Features

• 7000-Series Aluminum Collar (450 MPa yield strength)– Alternating RH and LH laminations joined into pairs with press-fitted pins

(spot welding not an option with this grade of aluminum).– Single tapered collaring key per quadrant– Mid-plane stop to prevent over-compressing coil during yoke assembly– Titanium pole inserts

• Laminated inner and outer iron yoke– Large slots for bladders– Alignment key in-line with coil pole– Large helium bypass hole

• 25mm thick Aluminum shell• 10mm thick stainless steel shell (not modeled here)

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2-D Magnetic Analysis

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Large Bypass Hole

Yoke Alignment Key

Bladder Slot

Outer Yoke

Aluminum Shell

Area Plot Coil Nodal Force Vector Plot

2-D Magnetic Analysis – (cont’d)

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12.3 Tesla

Magnetic Flux Contour Plot

2-D Mechanical Analysis (Collared Coil)

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12.3 Tesla

Azimuthal Coil Stress during Collaring

Maximum Azimuthal Coil Stress at Inner Coil Pole = 50 MPa

Note: Actual coil stress per unit length is ½ of this due to interlocking collar design

2-D Mechanical Analysis (Collared Coil) – cont’d

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Maximum collar Key Lug Stresses (Von Mises) during Collaring

2-D Mechanical Analysis (full C.S.)

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ANSYS Element Plot for Mechanical FEM

2-D 8 or 6-node structural solid elements as well as contact elements at interfaces

Friction coeff. = 0.2

Five load steps:1 – Collared (baseline)2 - Full Bladder Pressure3 - Yoke shims installed – bladders off4 - Cool-down to 4.3K5 - Power to 200 T/m peak flux gradient

2-D Mechanical Analysis (full C.S.)- cont’d

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Material Properties

2-D Mechanical Analysis (full C.S.)- cont’d

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Step 1: Collared Coil in Iron – Warm Without Yoke shims

Coil stress = 22 MPa

2-D Mechanical Analysis (full C.S.)- cont’d

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Step 2 – Full Bladder Pressure applied (47 MPa)

2-D Mechanical Analysis (full C.S.)- cont’d

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Step 3 – Insert Shims, Remove Bladder Pressure

Pole shim: .48 mm

Middle shim: .84 mm

Mid-plane shim: 1.08 mm

2-D Mechanical Analysis (full C.S.)- cont’d

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Step 4 – Cool-Down to 4.3K

Lateral Coil Defl.

-191 MPa

2-D Mechanical Analysis (full C.S.)- cont’d

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Step 5 – Apply Current to reach 200 T/m peak flux gradient

Lateral coil defl.

(tension)

2-D Mechanical Analysis (full C.S.)- cont’d

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Summary of Shell and Coil Stresses During Assembly and Operation

(tension)

Conclusions

• FE analysis results indicate that this design has merit– At no point during assembly and operation do coil azimuthal stresses

exceed 200 MPa.– At no point during assembly and operation does the bearing stress at

the collar mid-plane stop reach yield (with relief set at .1mm).– Collar strength is adequate (based on lug stresses).– Non-uniform yoke shimming yields the best results (assuming an

insertion clearance of .13mm).– The innermost portion of the inner coil pole goes into tension (27 MPa)

at full power.– Coil lateral deflection is 100 microns outward at the mid-plane

• Due to strain, not clearance take-up• Bladder Pressure is manageable (47 MPa {6800 psi}.

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Recommendations and Remaining Tasks

• This design requires further optimization– Perform a complete analysis of the collars including the press-fit

structural shear pins– Look at possible ways to reduce lateral movement of the coil at the mid-

plane– Further investigate using a stainless steel inner shell in place of

aluminum.• Eliminates the need for a separate inner shell• So far, this has not been successful

– Attempt to reduce coil tension against the pole• Increase collaring pre-stress

– Consider replacing tapered collaring key with a stainless steel clamp (i.e., “keeper”)

» Eliminates the 50% loss of pre-stress due to interlocking lugs» Eliminates the need for shear pins

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