WBS1 – Stellarator Core Recent Progress and Plans

1. WBS1 – Stellarator Core Recent Progress and Plans David Williamson NCSX Engineering Meeting September 10, 2002

2. WBS-1 near term tasks seek to develop, improve CDR design Major tasks through FY02: Improve port design for x-ray tomography, other diagnostics. Evaluate inboard PF coil positions. Analyze potential errors in coil position, tolerance. Modify PFC boundary to increase space for plasma, divertor, RF. Increase shell thickness in high-stress areas. Update modular coils to healed set with better properties, more space for internals. Define interface between shell segments. Define interface between TF coils and solenoid. Prepare specification, drawings for coil and vessel manufacturing development. Improve modular coil cooling concept.

3. Most important tasks: Improve vessel and modular coil geometry • Plasma-wall gap of 4-cm inside, 4-8 cm in divertor region is necessary for good connection length • Two options to improve spacing are 1) shift plasma outward, and 2) move winding surface / coils • Main issues are assembly of coils over vessel and schedule for establishing baseline modified vessel modified first wall vessel plasma PFCs 110201 3.8-cm modified CDR x-sec at 30-deg Proposed PFC mod Proposed winding surface mod

4. Other modular coil details are needed for prototype manufacture Completed tasks: Thermal analysis indicates that an assembly of copper plates between the winding pack and tee, copper mesh on the outside of the winding pack, and LN2-cooled, copper brackets every 10-in will adequately cool the conductor between pulses without ratcheting. (HM Fan) Structural analysis of the shell indicates that 1-in dia bolts on approx 8-in centers are sufficient for normal magnetic loads. The shell is not bolted in some inboard regions due to access limitations. (F. Dahlgren) Coil tolerance studies indicate that increasing the winding center TP tolerance from 1.5-mm to 3-mm in regions that are far from the plasma is feasible. (A. Brooks) Tasks in progress: Eddy current analysis is being performed to determine the poloidal time constant of the winding forms. A preliminary estimate is 50-250 ms, depending on the copper cooling plate configuration. Pro/E models of the winding forms are being modified to improve shell thickness in places, and make the models easier to change in the future. Univ of Tennessee is fabricating a small test coil using prototype conductor. The coil will have VPI, testing performed at PPPL. Other samples to be tested for mechanical properties, keystoning, etc.

5. Modular Coil Cooling Option #6 Cooling tube along perimeter of clamp Temperature Plot at The End of 1st Cooling Period Temperature constraint = 80K Conductor cable: 75% copper 25% epoxy Copper sheet Copper mesh Copper sheets Copper clamp Clamp spacing = 10” Clamp plate width = 2.5”, thickness = 0.375” Thickness of conductor insulation = 0.03” Thickness of coil ground wrap = 0.03” Copper sheet thickness = 0.085” Copper mesh thickness = 0.0394” HMF 090402

6. Structural Shell Bolt Stress at 60-deg Section 1-in dia bolt 0.5-in shim FD 082802

7. Tolerance Study Summary • Impact of Random Tolerance Stack up for Different Tolerances in Modular, TF and PF • Softening Tolerance on TF & PF from 1.5 to 3.0 mm appears acceptable • Softening Overall Tolerance on Modulars notacceptable. • Softening Modular Tolerance based on plasma separation (1.5mm near plasma to 3.0 far from plasma ) has minimal impact • Impact of short “wavelet” type deformation on Modular Coils • Coil-to-Plasma Separation less than 30 cm has strongest impact on island size • In-plane and Out-of-Plane deformations do not differ significantly • Impact of broad deformations of Modular Coils • Increasing Length of deformation does not Increase Max Island Size AWB 073102

8. Other vacuum vessel tasks: Spacer used for x-ray tomography • Requirements: • Camera size 50 mm x 50 mm x 25 mm • Thin face toward plasma • Number of cameras 10 to 12 located at the oblate plane if possible or on one side of the spacer. • Camera must be cooled during bakeout • One cable for each camera

9. Other vacuum vessel tasks: Diagnostic ports updated Thomson Scattering Port Laser Vertical-cut 39deg off vertical Laser path 20020626-wbs-1-mtg.ppt MJC 062602

10. Other tasks: Proposal to combine PF3 and PF4 New coil needs 1+ MAT capability Propose to keep PF3 cross section (14 turns vert, 8 radial), move linearly halfway radially and vertically towards PF4 along vector through cross section centers. PF4 PF3 Dimensions in inches

11. Other tasks: Structural analysis of TF inboard support TF coil inward electromagnetic forces are transferred either to bucking plates or to the poloidal field (PF) coils in the central solenoid. When the TF forces are resisted by the PF coils, which are normally under ring tension, the PF coils are effective in counter-balancing the TF inward net loads. However, the stresses in the TF coils are higher when the PF coil currents go to zero. The study also showed that adding a wedge-shaped piece to extend the height over which centering forces are reacted, significantly reduces the stresses in the TF coil. Either support option appears feasible. TF Coil PF2 PF1 HMF 062602

12. Stellarator Core Issues Modular Coils: • Need to select coil set, update geometry • Winding form time constant is a concern • Need tests to determine winding properties Vacuum Vessel / PFC: • Need to establish space envelope • Adjust port configuration for final coil set • Verify assembly plan using physical models PF / TF Coils: • Impact of PF coil proposal on power systems • Need to select option for supporting TF / solenoid