EVOLUTION OF VISIONS FOR TOKAMAK FUSION POWER PLANTS

1. EVOLUTION OF VISIONS FOR TOKAMAK FUSION POWER PLANTS Farrokh Najmabadi University of California, San Diego, La Jolla, CA, United States of America IEEE 19th Symposium on Fusion Engineering (SOFE 19) January 22-25, 2002 Atlantic City, NJ You can download a copy of the paper and the presentation from the ARIES Web Site: ARIES Web Site: http://aries.ucsd.edu/ARIES/

2. The ARIES Team Has Examined Several Magnetic Fusion Concept as Power Plants in the Past 14 Years • TITAN reversed-field pinch (1988) • ARIES-I first-stability tokamak (1990) • ARIES-III D-3He-fueled tokamak (1991) • ARIES-II and -IV second-stability tokamaks (1992) • Pulsar pulsed-plasma tokamak (1993) • SPPS stellarator (1994) • Starlite study (1995) (goals & technical requirements for power plants & Demo) • ARIES-RS reversed-shear tokamak (1996) • ARIES-ST spherical torus (1999) • Fusion neutron source study (2000) • ARIES-AT advanced technology and advanced tokamak (2000) • ARIES-IFE assessment of IFE chambers (current research)

3. Top –Level Requirements for Commercial Fusion Power • Have an economically competitive life-cycle cost of electricity: • Low recirculating power; • High power density; • High thermal conversion efficiency; • Less-expensive systems. • Gain Public acceptance by having excellent safety and environmental characteristics: • Use low-activation and low toxicity materials and care in design. • Have operational reliability and high availability: • Ease of maintenance, design margins, and extensive R&D. • Reasonable Extension of Present Data base • Physics: Solid Theoretical grounds and/or experimental basis. • Technology: Demonstrated at least in small samples. ARIES Research Aims at a Balance Between Attractiveness & Feasibility

4. Power Plant Physics NeedsAnd Directions for Burning Plasma Experiments

5. Physics needs of pulsed and steady-state first stability devices are the same (except non-inductive current-drive physics). Pulsar ARIES-I’ Current-drive system PF System Very expensive but efficient Non-inductive drive Expensive & inefficient Recirculating Power Low High Optimum Plasma Regime High Bootstrap, High A, Low I High Bootstrap, High A, Low I Current profile Control No, 30%-40% bootstrap fraction bN~ 3, b ~ 2.1% Yes, 65-%-75% bootstrap fraction bN~ 3.3, b ~ 1.9% Toroidal-Field Strength Lower because of interaction with PF (B ~ 14 T on coil) Higher (B ~ 16 T on coil) Power Density Low Medium Size and Cost High (~ 9 m major radius) Medium (~ 7 m major radius) For the same physics and technology basis, steady-state devices outperform pulsed tokamaks

6. Increase Power Density Power density, 1/Vp What we pay for,VFPC High-Field Magnets • Little Gain Big Win • ARIES-I with 19 T at the coil (cryogenic). • Advanced SSTR-2 with 21 T at the coil (HTS). D r r > D r ~ D r < D High bootstrap, High b • 2nd Stability: ARIES-II/IV • Reverse-shear: ARIES-RS, ARIES-AT, A-SSRT2 Decrease Recirculating Power Fraction Directions for Improvement • Improvement “saturates” at ~5 MW/m2 peak wall loading (for a 1GWe plant). • A steady-state, first stability device with Nb3Sn technology has a power density about 1/3 of this goal. • Improvement “saturates” about Q ~ 40. • A steady-state, first stability device with Nb3Sn Tech. has a recirculating fraction about 1/2 of this goal.

7. Second Stability Regime Reverse Shear Regime Reverse Shear Plasmas Lead to Attractive Tokamak power Plants • Requires wall stabilization (Resistive-wall modes) • Poor match between bootstrap and equilibrium current profile at high b. • ARIES-II/IV: Optimum profiles give same b as first-stability but with increased bootstrap fraction • Requires wall stabilization (Resistive-wall modes) • Excellent match between bootstrap & equilibrium current profile at high b. • ARIES-RS (medium extrapolation): bN= 4.8, b=5%, Pcd=81 MW (achieves ~5 MW/m2 peak wall loading.) • ARIES-AT (aggressive extrapolation): bN= 5.4, b=9%, Pcd=36 MW (high b is used to reduce peak field at magnet)

8. Approaching COE insensitive of power density Approaching COE insensitive of current drive Evolution of ARIES Designs

9. Estimated Cost of Electricity (c/kWh) Major radius (m) High Thermal Efficiency High b is used to lower magnetic field Approaching COE insensitive of power density Our Vision of Magnetic Fusion Power Systems Has Improved Dramatically in the Last Decade, and Is Directly Tied to Advances in Fusion Science & Technology

10. Confinement Experiments Burning Plasma Experiments Power Plant What About Confinement Time? • Global confinement time is critical as • Plasma stored energy = Heating power / Confinement time • Improved global confinement means we can build a smaller (fusion power) machine. • After machine is operational, confinement better than needed for ignition has to be degraded! • Power plant size is set by economy of scale of fusion power density. All ARIES designs require confinement performance similar to present experiments: H(89P) ~2-3. A better confinement has to be degraded! • Understanding (and manipulating) local transport is critical to optimizing plasma profiles.

11. Fusion Technologies Have a Dramatic Impact of Attractiveness of Fusion

12. SiC composites are attractive structural material for fusion ARIES-I Introduced SiC Composites as A High-Performance Structural Material for Fusion • Excellent safety & environmental characteristics (very low activation and very low afterheat). • High performance due to high strength at high temperatures (>1000oC). • Large world-wide program in SiC: • New SiC composite fibers with proper stoichiometry and small O content. • New manufacturing techniques based on polymer infiltration or CVI result in much improved performance and cheaper components. • Recent results show composite thermal conductivity (under irradiation) close to 15 W/mK which was used for ARIES-I.

13. ARIES-I: • SiC composite with solid breeders • Advanced Rankine cycle Many issues with solid breeders; Rankine cycle efficiency saturated at high temperature • Starlite & ARIES-RS: • Li-cooled vanadium • Insulating coating Max. coolant temperature limited by maximum structure temperature • ARIES-ST: • Dual-cooled ferritic steel with SiC inserts • Advanced Brayton Cycle at  650 oC Improved Blanket Technology High efficiency with Brayton cycle at high temperature • ARIES-AT: • LiPb-cooled SiC composite • Advanced Brayton cycle with h = 59% Continuity of ARIES research has led to the progressive refinement of research

14. ARIES-AT Fusion Core

15. Simple, low pressure design with SiC structure and LiPb coolant and breeder. ARIES-AT2: SiC Composite Blankets Outboard blanket & first wall • Simple manufacturing technique. • Very low afterheat. • Class C waste by a wide margin. • LiPb-cooled SiC composite divertor is capable of 5 MW/m2 of heat load. • Innovative design leads to high LiPb outlet temperature (~1,100oC) while keeping SiC structure temperature below 1,000oC leading to a high thermal efficiency of ~ 60%.

16. PbLi Inlet Temp. = 764 °C Max. SiC/SiC Temp. = 996°C Max. SiC/PbLi Interf. Temp. = 994 °C Bottom Top PbLi Outlet Temp. = 1100 °C Innovative Design Results in a LiPb Outlet Temperature of 1,100oC While Keeping SiC Temperature Below 1,000oC • Two-pass PbLi flow, first pass to cool SiCf/SiC box second pass to superheat PbLi

17. T 1 11 He Divertor 2' 10 Coolant 2 9' Blanket Divertor 9 5' 7' 3 8 LiPb 6 4 Blanket S 11 Coolant 9 10 Intermediate Intercooler 1 Intercooler 2 HX Recuperator 3 1 Compressor 1 8 6 7 5 W net Compressor 3 Turbine Compressor 2 2 4 Heat Rejection HX Advanced Brayton Cycle Parameters Based on Present or Near Term Technology Evolved with Expert Input from General Atomics* • Key improvement is the development of cheap, high-efficiency recuperators.

18. Multi-Dimensional Neutronics Analysis was Performed to Calculate TBR, activities, & Heat Generation Profiles • Very low activation and afterheat Lead to excellent safety and environmental characteristics. • All components qualify for Class-C disposal under NRC and Fetter Limits. 90% of components qualify for Class-A waste. • On-line removal of Po and Hg from LiPb coolant greatly improves the safety aspect of the system and is relatively straight forward.

19. YBCO Superconductor Strip Packs (20 layers each) CeO2 + YSZ insulating coating (on slot & between YBCO layers) Inconel strip 430mm 8.5 Use of High-Temperature Superconductors Simplifies the Magnet Systems • HTS does not offer significant superconducting property advantages over low temperature superconductors due to the low field and low overall current density in ARIES-AT • HTS does offer operational advantages: • Higher temperature operation (even 77K), or dry magnets • Wide tapes deposited directly on the structure (less chance of energy dissipating events) • Reduced magnet protection concerns • And potential significant cost advantages Because of ease of fabrication using advanced manufacturing techniques

20. ARIES-AT Also Uses A Full-Sector Maintenance Scheme

21. Pulsar (pulsed-tokamak): • Trade-off of b with bootstrap • Expensive PF system, under-performing TF For the same physics & technology basis, steady-state operation is better • ARIES-I (first-stability steady-state): • Trade-off of b with bootstrap • High-field magnets to compensate for low b Improved Physics Need high b equilibria with aligned bootstrap • ARIES-RS (reverse shear): • Improvement in b and current-drive power • Approaching COE insensitive of current drive Better bootstrap alignment More detailed physics • ARIES-AT (aggressive reverse shear): • Approaching COE insensitive of power density • High b is used to reduce toroidal field Continuity of ARIES Research Has Led to the Progressive Refinement of Plasma Optimization

22. Pulsar (pulsed-tokamak): • Trade-off of b with bootstrap • Expensive PF system, under-performing TF “Conventional” Pulsed plasma: Explore burn physics • ARIES-I (first-stability steady-state): • Trade-off of b with bootstrap • High-field magnets to compensate for low b Demonstrate steady-state first-stability operation. Improved Physics • ARIES-RS (reverse shear): • Improvement in b and current-drive power • Approaching COE insensitive of current drive • Explore reversed-shear plasma • Higher Q plasmas • At steady state • ARIES-AT (aggressive reverse shear): • Approaching COE insensitive of power density • High b is used to reduce toroidal field Explore envelopes of steady-state reversed-shear operation ARIES designs Correspond to Experimental Progress in a Burning Plasma Experiment

23. Advanced Technologies Have a Dramatic Impact on Fusion Power Plant Attractiveness Technologies • High-performance, very-low activation blanket: • High thermal conversion efficiency; • Smallest nuclear boundary. Impact • Dramatic impact on cost and attractiveness of power plant: • Reduces fusion plasma size; • Reduces unit cost and enhanced public acceptance. • High-temperature superconductors: • High-field capability; • Ease of operation. • Simpler magnet systems • Not utilized; • Simple conductor, coil, & cryo-plant. • Advanced Manufacturing Techniques • Utilized for High Tc superconductors. • Detailed analysis in support of: • Manufacturing; • Maintainability; • Reliability & availability. • High availability of 80-90% • Sector maintenance leads to short schedule down time; • Low-pressure design as well as engineering margins enhance reliability.