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Stellarator magnets

Explore the benefits of using dual-temperature superconductors like MgB2 and NbTi in magnet design for plasma fusion applications. Discuss costing algorithms, structural considerations, and the impact on cost and complexity. Evaluate the potential for rapid prototyping methods in manufacturing large structures.

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Stellarator magnets

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  1. Stellarator magnets L. Bromberg J.H. Schultz MIT Plasma Science and Fusion Center ARIES meeting March 8-9, 2004

  2. Organization of talk • Magnet design with dual temperature superconductor • MgB2 and NbTi • Costing algorithm • Future work

  3. Medium Temperature Superconductor

  4. Preliminary designMgB2 Needed for determination of radiation effects on magnet due to B in the SC

  5. Algorithm for low Tc coil

  6. Manufacturing • Inserted from the plasma side into large structures. • If wound. substantial amount of strain capability required for assembly • Nb2Sn requires low strain • MgB2 has similar low strain capability • (both require react and wind) • Stuck with either NbTi (at low temperature at high field) or high temperature superconductor.

  7. Multiple temperature operation? • By using either MgB2 or BSSCO, it is possible to grade the magnet for cost reduction • Use NbTi at 4 K for the low temperature region • The low field region is further removed from the plasma as is better shielded.

  8. Method for performing dual temperature - Option 1 • Radiation captured at the higher temperature • Need to transfer loads through low temperature region (one insulation region required)

  9. Method for performing dual temperature - Option 2 • Substantially decreased thermal loads • Need to transfer outward loads from high temperature region through low temperature region before getting to structure (if bucking): two insulation regions.

  10. Dual temperature • Impact mainly on cost. • Tradeoff: • Much cheaper superconductor if using dual temperature • But • More complicated arrangement • Need for 4 K refrigerator • Final design will investigate both

  11. Design/Costing algorithms • Prepared simple spread sheet model for designing coils and costing • Coil designs (conductor) • Simple coil (one type of conductor) and coils with multiple types of conductors • Coil structure • Coil cost • Spread sheet transferred to Jim Lyon

  12. Using design by J. Lyon(presented in Dec. meeting) • Coil aspect ratio small • There may be sufficient space between coils without having to change the winding pack shape

  13. Coil structure • Assumes that all space between coils is filled with structure • Regions for access ports need to be reinforced elsewhere • Conservative assumption • Subtraction of relatively large numbers for estimating the volume • Good for system code. Will be improved once design space is narrowed down.

  14. Calculation of external structure • Using simple beam theory (good for system analysis) • A = B02 R02/2 m0 • S1 = A (R2 ln(R2/R1) - R2 +R1)/(R1 (R2-R1)) • S2 = A (R2 - R1 - R1 ln(R2/R1))/(R2 (R2-R1)) • t1 = S1/ sm ; t2 = S2/ sm • R3 = (S1 R12 + S2 R22)/(A ln(R2/R1)) • a = 3/8 S2 R2 (R2-R3)/sb / R3) • R2: outer external structure radius • R1: inner external structure radius

  15. Design criteria for external support • Use SS-316 because of the large amounts of materials required could have substantial cost penalty • Cross section of support determined by bending • Maximum stress by lowest of 1.5 x greater of (2/3 sy or 1/3 su) • Use around 800 MPa (for SS-316) • SS-316: (1400 MPa yield, 1800 MPa ultimate)

  16. Bucking cylinder and total structure cost • Large structure with tight tolerances. • $50/kg may be an underestimate • Can we use rapid prototyping methods for manufacturing of these large structures?

  17. Total coil costing • Cost of magnet dominated by winding assembly • Cost of BSCCO would be larger than that of Nb3Sn

  18. Magnet design • Very aggressive IFE magnet design ran into a lot of resistance (from the reviewers of Fusion Eng Design article) • I propose that the baseline be wound magnet • BSCCO and NbTi, if cost warrants • Else, just BSCCO • Use aggressive design as option

  19. Work to be done • System design tools have been developed • Detailed calculations need to be performed for a design point, in order to assure the appropriateness of the algorithms • Calculate stresses using actual currents and geometries • Structural considerations • Deformations and strains of the structure and superconductor • Superconductor characteristics • Power supplies • Cryogenic loads and cooling • Need one design point to calculate some details • NCSX (??) • HSR

  20. Resources • Can PPPL provide assistance with the calculations of the loads? • Stresses? • P. Titus has been performing calculations for NCSX, but only earthquake analysis

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