TF Coil Radial Preload Required for Structural Stability

TF Coil Radial Preload Required for Structural Stability NCSX • A. Brooks has identified some time points in the reference current scenarios which produce an unstable force distribution on the TF coils (positive net radial force and torque about major radius). • This occurs when MC currents are high and the TF coil current is relatively low. TF Coil Preload Design Iteration 1

Comparison of Deformations from Slipped and Stuck TF Coils NCSX Zero Radial Preload Allows Coils to Slip at Interface Radial Preload Sufficient to “Stick” Coils at Interface (old 2 x 6 WP) (new 3 x 4 WP) TF Coil Preload Design Iteration 2

Wedge-to-Wedge Friction Coefficient ( ) as a Function of Radial Preload NCSX • • A 4000 lb preload will produce a “stuck” coil set if >0. 1. This is a factor of 2 below the 0. 2 value which is expected to be easily achieved. TF Coil Preload Design Iteration 3

Radial Preload Applied to Back Leg NCSX Back SS Strap Radial Pre-load SS Wedge Castings Wedging • Radial pre-load required to ensure wedging TF Coil Preload Design Iteration 4

Breakout of Reaction Structures, Radial Preload NCSX • • 4, 000 LBF per pusher provides twice the required pre-load to prevent any movement as TF Fields ramp up or down • Bellville washers in parallel provide relatively constant force over required thermal excursions Radial preload applied with jack screw device top and bottom. TF Coil Preload Design Iteration 5

Breakout of Reaction Structures, Wedging NCSX Wedging fixes location while shim bags lock coil in case with respect to Wedging Extends supports 50 degrees around the upper and lower TF Locking Pins add redundancy to wedging design Castings extend as High as the Upper TF Support Castings TF Coil Preload Design Iteration 6

Centering Forces for TF Only NCSX • Centering forces concentrate on inner leg • Moving preload to inner leg removes unnecessary stress TF Coil Preload Design Iteration 7

Jack Screw Device Added Pulls Coil Forward NCSX • Use available space for preload jacking screws instead of pins Bellville washers ensure constant 4000 lbf load TF Coil Preload Design Iteration 8

Jack Screw Device Added Pulls Coil Forward NCSX TF Coil Preload Design Iteration 9

Top Down View, Center Stack NCSX • Nuts accessible for maintenance from top of vessel TF Coil Preload Design Iteration 10

Access Holes In Top Hat Structure NCSX • Removal of PF 4 allows for access to bracket hardware TF Coil Preload Design Iteration 11

Jack Screw Device Added Pulls Coil Forward NCSX TF Coil Preload Design Iteration 12

TF Coil Bonded to Casting With Front Preload NCSX • Model updated to reflect preload application at front of coil directly to wedge castings TF Coil Preload Design Iteration 13

Deflections With Front Preload and Cool Down NCSX • Preload contributes little or no deflection before application of operating load TF Coil Preload Design Iteration 14

Stresses Due to Preload +. 5 Tesla TF Only Operation NCSX • Compares to 195 MPa for unbonded back leg preload run • Bonded Bending Stress at 127 MPa • Early results show about 177 MPa for unbonded front preload TF Coil Preload Design Iteration 15

New TF Flag Design NCSX TF Coil Preload Design Iteration 16

Breakout of Reaction Structures, Vertical Support NCSX • Lower Support reacts gravity load and fixes vertical position. • Allows for Outward radial motion TF Coil Preload Design Iteration • Upper Support allows for application of upward or downward load. • Allows for Outward radial motion 17