1. 1 1. Cover Page S. NISHIO Japan Atomic Energy Agency, Naka Fusion Institute, Naka-shi, Ibaraki-ken 311-0193, Japan nishio.satoshi@jaea.go.jp US - Japan Workshop on Power Plant Studies and Related Advanced Technologies with EU Participation, 24-25 January, 2006 at UC San Diego, 584 EBU-II Magnets of Tokamak Reactor : the indispensable & (but) burdensome existence

2. 2 Contents ● TFC Cost is Major Part of Total Cost ● Lightweight TFC leads to Low Cost Tokamak ● 1st step lightening : Reactor Concept Modification ● 2nd step lightening : Coil Concept Improvement Having an Eye on Low Cost Tokamak Reactor

3. 3 Reactor Concept Modification P f = 3 GW, P n = 5 MW/m 2 Normalized Beta,  N P f  t 2 B 0 4  N 2 B 0 2 8 8 Wt ~ 3500 ton MassiveLightweight Wc < 2000 ton Wc > 15000 ton Low A Concept Leads to Lightweight TFC

4. 4 Reactor Weight & TFC B max, CSC Bore VECTOR ITER SSTR J-DEMO ARIES-ST ● CS-less & high field TFC leads to lightweight Tokamak Contour Map of Reactor Weight

5. 5 Empirical Scaling for Magnet Weight M : Structure Weight  : Mass Weight Density E : Stored Energy Q : Geometry Factor (1 ～ 3)  : Design Stress Virial Theorem  =7900kg/m 3 Q =3  =400MPa X X VECTOR ARIES-RS Magnet Weight (Ton) Stored Energy (GJ) ARIES-RS TFC, Why SO LIGHTWEIGHT ?

6. 6 Coil Concept Improvement Indirect (Conduction) Cooling & TFCs, PFCs Integrated Structure

7. 7 Cooling Methods Pool Boiling ● Low Tech. ● Poor Mech. Strength ● Low Insulation Voltage Forced CoolingConduction Cooling ● Good Heat Removal ● High Insulation Voltage ● Severe Pressure Drop ● Excellent Mech. Strength ● poor Heat Removal

8. 8 Windings of Forced Cooling System Current path and coolant path are not independent each other.

9. 9 For Poor Heat Removal of Conduction Cooling Stabilization of High Temp. Super-Conductor (YBCO) is designed to be done with the enthalpy of the YBCO material itself, rather than by cooling with supercritical helium against the disturbances such as movement etc. Heat capacity : 500 mJ/cm 3 for the temperature range between 33 and 35 K

10. 10 Structure of Winding Higher fieldMiddle fieldLower field Size of winding pack478 mm x 174 mm 398 mm x 150 mm 272 mm x 127.2 mm No of pancakes444 No of turns1048852 Thickness of cooling plate10 mm Current density50 A/mm 2 59 A/mm 2 60 A/mm 2 Parameters of winding packs Each coil has three (higher, middle and lower field) winding packs installed into the coil case.. To reduce stress (or strain) on the winding and to control the occurrence of flux jumps, three slots are machined into the coil case in which each winding pack is installed.

11. 11 Structure of TF coil

12. 12 For Quick Response for I P Control VECTOR ITER SSTR J-DEMO ARIES-ST Slim CSIron CoreSolenoid Free Flux supply & Mechanical toughness

13. 13 Summary ● CS-less (Low A) concept leads to lightweight Tokamak. ● Conduction cooling method leads to lightweight TFC. ● High temp. superconductor meets conduction cooling. ● Cs-less & iron core concept may meet the requirements for quick Ip control and TFC mechanical strength.