NSTX Center Stack Joint Design and Analysis

Presented by P. Heitzenroeder

Outline

• A Review of the Machine General Arrangement

• Center Stack Loads• Reaction of Center Stack Loads• The Original Analysis• Why Did Failure Occur?• Planned Design Improvements• Summary

NSTX General Arrangement

CS Hub Region Details

Description of CS Loads

2. Lateral loads on flags due to ITF x Bz

3. Vertical loads on flags due to ITF x Btf

4. Torque on TF bundle due to ITF XBOH

5. Torques on TF bundle due to ITF XBPF1A

1. Vertical load from flexible connector between outer TF legs and flags.

Description of CS Loads(continued)

Load (6) Gravity loads (ie, weight of TF CS leg bundle, OH coil, PF 1 coils, vacuum shell).

Load (7) OH and PF coil EM loads

Load (8) Loads to thermal expansion.

Load (9) Lateral loads on the CS due to halo current asymmetry.

Reaction of Vertical Loads (1) and (3) on Flags

• Vertical Loads (1) and (3) are reacted by tightly shimming the flags top and bottom to a hub structure.

• Ideally the hub will react the moment, leaving only vertical loads to be reacted.

• Vertical loads reacted at joint interface and at torque collar.

Fvertical

(lbs)

dR from point of application

to flag inboard edge

(in)

Moment w.r.t. point X

(in-lbs)

Inner Tier Flag 7380 4.3 31719

Inner Tier Link 1855 13.8 25652

Outer Tier Flag 1845 4.3 7930

Outer Tier Link 464 13.8 6413

Total from All Turns 249324

1

3

(2) Lateral Loads on Flags

• Flags are wedged in the hub structure to create a solid disc-like assembly.

• 2 load paths to react net torque on the hub structure:– At the interface between

the flag and CS TF conductor;

– To the VV via the spline (top) or torque plate(bottom).

Flag

Wedge

Reaction of Torques (4) and (5) on Center Stack TF Bundle

• The torques imposed on the center stack (22480 ft-lbs.) are reacted by “grabbing” the CS by collars at both ends of the solenoid.

• Collars are connected to hub structures which in turn react the torque through the vacuum vessel via a spline.

• The spline permits free axial thermal growth of the center stack.

Center stack

Collar

Load (6): Gravity Loads

Load (6): The weight of the CS, OH, and PF coils are supported on a pedestal on the bottom of NSTX.

Avoidance of Thermally Induced Loads (8)

• Flexible links between outer TF coil legs and CS TF bundle permits vertical thermal expansion.

(9) Lateral Loads on CS Bundle

• Lateral loads due to halo currents were found to be benign.

• A guide structure at the upper end ois provided to assure vertical alignment.