N. Dhanaraj, Y. Orlov, R. Wands Thermal-Stress Analysis of CC1 Space Frame

Outline Background and Motivation Design Changes Assembly and Loading Sequence Finite Element Analysis Strategy Analysis and Results Summary

Background and Motivation  The Superconducting cavity in the Capture Cavity 1 (CC1) cryomodule is mounted on a space frame structure.  There has been a recent plan to upgrade this cryomodule by replacing the cavity and lever tuner set up with a newer 1.3 GHz 9-cell cavity and blade tuner.  This upgrade has invoked a thermal-stress verification of the space frame support structure.  The following slides will provide the details of the thermal-stress analysis and the basis to deem the safety of the upgrade and also address recommendations from previous review.

3D Model of Space Frame with Cavity G10 Support Rods Dressed Cavity

3D Model of Space Frame G10 Support Rods G10 Support System to Control Longitudinal Motion of the Support Frame Aluminum Support Frame SS Bearing Blocks to seat the Dressed Cavity

Design Changes N

Assembly and Loading Sequence  The assembly sequence dictates the various loads acting on the space frame and the G10 support rods, thus defining this assembly procedure is critical.  Assembly Procedure of Main Components: 1. The dressed cavity is mounted on the aluminum frame and the assembly is loaded on to a cart. 2. The cart is rolled into the cryomodule. 3. The top G10 rods are used to lift the cavity assembly and then locked in position. 4. The cart is rolled out and the bottom G10 rods and snug fit before cool down. 5. After cool down all G10 rods should see tensile forces that should produce stresses that fall within the allowable limits for the material to ensure proper design.

Finite Element Analysis Strategy FEA Strategy: Perform a static structural analysis to simulate the loading of the top G10 rods as they counter the weight of the cavity assembly by fixing the top rods and allowing the bottom rods to displace along its length. Note the displacements of the bottom rod warm ends and place these displacements as constraints on those rod ends. This is the amount by which the top rods must be lifted. Perform a thermal-stress analysis to simulate the cool down procedure by assigning temperature boundary conditions to the various components and check the eventual stresses against the failure criteria. Albeit First Thermal in ANSYS

FEA Models Meshed Model – nodes, elements Half Symmetry Model

Static Structural – Loading of Upper G10 Rods Fixed Ends Free to move along length Free along Z 4X Rz = Free 1/4 th ( N)

Results – Forces and Displacements Fz = N Uz = mm Uz = mm Fz = N Uz global= mm

Results – Stresses in Frame From the Aluminum Association, Specifications for Aluminum Structures (FOS > 1.5): Maximum fiber stress for 6061-T6 unwelded = 131 MPa Maximum fiber stress for 6061-T6 welded = 75.8 MPa

Results – Rod Forces and Stresses Rods Fz along length of Rod - N Rod Axial Stress - MPa Rod Rod Rod 300 Rod 400

Thermal Analysis A A B B A B C B A

Results – Temperature Profile

Heat Loads W

Combined Thermal-Structural Displacements Uz set from previous analysis Rod 1 Rod 2 Rod 3 Rod 4

Results – Rod Forces and Stresses Rods Fz along length of Rod - N Rod Axial Stress - MPa Rod Rod Rod Rod

Results – Stresses in Frame From the Aluminum Association, Specifications for Aluminum Structures (FOS > 1.5): Maximum fiber stress for 6061-T6 unwelded = 131 MPa Maximum fiber stress for 6061-T6 welded = 75.8 MPa Verification of High stress: Stress classification line through weld gives membrane stress 88.5 MPa and membrane + bending MPa which are well below the allowables for secondary stresses of 1.5 Sm for membrane and 3 Sm for membrane + bending from ASME VIII Div. 2.

Results - Displacements Cavity axis Lateral Range 2.3 to -2.1 mm Range 0.75 to -2.8 mm Range 1.4 to -0.9 mm Z

Beam Tube Radiation Heat Load Assumptions: Steady state conditions, surroundings approximated as blackbody. Emissivity of inner beam tube surface = 0.16 (unpolished or slightly polished copper surface) Heat load from 300 K to 2 K is 0.3 Watts 300 K surroundings 2 K 450 mm 78 mm

Summary  Thermal-stress analysis was performed on the CC1 space frame to match the assembly and loading sequence.  The stresses in the parts of concern were looked at (G10 rods) and the stresses were found to be significantly below the allowable limits.  There is no need for spring washers on the G10 rods as the forces experienced are very low.  The stresses in the aluminum frame was also analyzed and found to be below the allowables of Aluminum Association standards. No credit was taken for cold properties.  The displacements of the space frame due to thermal contraction are within the bellows capabilities.  The heat loads to 2 K /5 K junctions are very small.  The support structure is safe for the operation of the upgrade.