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Optimization of High-b Steady-State Tokamak Experiment

This study focuses on the optimization of a high-b steady-state tokamak burning plasma experiment based on a high-b steady-state tokamak power plant. It examines various designs and configurations to identify the most attractive possibilities. The study emphasizes realistic engineering constraints and aims to achieve a 100% non-inductive steady-state operation. The results provide valuable insights for future tokamak power plants.

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Optimization of High-b Steady-State Tokamak Experiment

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  1. Optimization of a High-b Steady-State Tokamak Burning Plasma Experiment Based on a High-b Steady-State Tokamak Power Plant D. M. Meade, C. Kessel, S. Jardin Princeton Plasma Physics Laboratory Presented at IEA Workshop on Optimization of High-b Steady-State Tokamaks General Atomics February 14, 2005

  2. Tokamak Based Power Plant Studies have Identified Attractive High-b Steady-State Configurations with A ≈ 4 • Three decades of systematic studies in the US have surveyed the range of possibilities available for a tokamak power plant and have identified the ARIES-RS/AT (A = 4) designs as the most attractive possibilities. • Other studies favoring highish aspect ratio for high-b steady-state include: TPX (A= 4.5), ITER-HARD (A = 4), ASSTR (A = 4) • The FIRE design studies initiated in 1999 adopted the ARIERS/AT physics and plasma technology design characteristics including : • Strong shaping –> Double null dx = 0.7, kx = 2, Aspect ratio ≈ 4 • Reactor level BT= 6 - 10 T and plasma density = 2 - 4 x 1020m-3 • LHCD/ICFWCD - no momentum input • All metal PFCs W divertor • Internal fast control coils • RWM coils integrated into FW of port plugs - LN cooled coils provide sufficient pulse length and small size –> low cost

  3. Optimization of Cu Coil BPX (e,.g, FIRE) • Optimization Depends on Goals and Constraints Realistic engineering constraints must be imposed • Optimization of inductively-driven BPX with Cu Coil (e,.g, FIRE) 1991 CIT Study (LLNL Super Code-Galumbos) W. Reiersen 2000 FIRE (FIRE Sale) J. Schultz 2001 FIRE (BPSC) S. Jardin,C. Kessel, D. Meade, C. Neumeyer • Optimization of High-b Steady-State Modes in FIRE 2002 SOFE Meeting FIRE AT C. Kessel 2002/2004 IAEA FIRE D. Meade et al References 1. J. Galumbos et al Fusion Tech. 13, 93, 1988 2. W. Reiersen 3. J. Schultz - 4. S. Jardin, C. Kessel et al Fusion Science and Technology 43, 161 2003 5. A High-Aspect-Ratio Design for ITER, J. C. Wesley et al Fusion Tech. 21, 1380 1992. 6. Y. Seki et al., (1991). Rep. JAERI-M 91-081, JAERI. Naka.

  4. CIT Optimization Using Super Code 1989 Compact Ignition Tokamak Optimized at A = 3.5

  5. The Systems Code was Updated and Calibrated Based on 3-D Finite Element Stress Calculations for FIRE. Confinement (Elmy H-mode) ITER98(y,2): E = 0.144 I0.93 R1.39 a0.58 n200.41 B0.15 Ai0.19 0.78 P heat-0.69 H(y,2) Density Limit:n20 < 0.75 nGW = 0.75 IP/a2 H-Mode Power Threshold:Pth > (2.84/Ai) n200.58 B0.82 R a0.81 MHD Stability:N =  / (IP/aB) < 3.0 PAUX, Q = PFUSION/PAUX, qCYLor qMHD,, ZEFF all held fixed Engineering Constraints: 1. Flux swing requirements in OH coil (V-S) 2. Coil temperature not exceed 373o K 3. Coil stresses remain within allowables Configuration Concept: 1. OH coils not linking TF coils, or 2. OH coils linking TF coils—ST-like Kessel, Jardin 2002

  6. 8T BT = 4T 6T 7T 5T 9T 10T Optimization of Cu Coil BPX (e,.g, FIRE) Using BPSC

  7. Optimization at Smaller Size and Higher Aspect Ratio as Confinement Improves Major Radius (m) 10T

  8. Optimization is not Sensitive to Variation of Elongation with Aspect Ratio Major Radius (m)

  9. No He Pumping bN = 1.8 Pf/V = 5.5 MWm-3 fbs ≈ 25% Normalized pulse length (tCR)in FIRE is the same as ITER

  10. Optimization of High-b Steady-State* Modes in a Cu Coil BPX (e,.g, FIRE) • Optimization of AT Modes in a specific FIRE (Fixed A, R, B < Bmax, etc) • Use a 0-D Systems Code to calculate a large data base(~ 50, 000) of possible solutions as parameter space is scanned. • Impose engineering constraints on pulse length (TF ohmic and nuclear heating, divertor target and baffle heat loads, vacuum vessel nuclear heating and first wall surface heating) to define operating space. • Use J_solver and PEST to validate stability and required current profiles. • Use TSC to confirm evolution of integrated discharge. * Steady-state = 100% non-inductive, dq/q < few % for several tCR , tdiv, tFW

  11. 0-D Operating Space Analysis for FIRE AT • Heating/CD Powers • ICRF/FW, 30 MW • LHCD, 30 MW • Using CD efficiencies • (FW)=0.20 A/W-m2 • (LH)=0.16 A/W-m2 • P(FW) and P(LH) determined at r/a=0 and r/a=0.75 • I(FW)=0.2 MA • I(LH)=Ip(1-fbs) • Scanning Bt, q95, n(0)/<n>, T(0)/<T>, n/nG, N, fBe, fAr • Q=5 • Constraints: • (flattop)/(CR) determined by VV nuclear heat (4875 MW-s) or TF coil (20s at 10T, 50s at 6.5T) • P(LH) and P(FW) ≤ max installed powers • P(LH)+P(FW) ≤ Paux • Q(first wall) < 1.0 MW/m2 with peaking of 2.0 • P(SOL)-Pdiv(rad) < 28 MW • Qdiv(rad) < 8 MW/m2

  12. FIRE’s Q = 5 AT Operating Space 5.0 400 4.5 300 4.0 3.5 200 3.0 100 2.5 H-Mode 0 2.0 1.2 2.0 1.0 1.4 1.6 1.8 1.0 0.8 0.6 0.4 0.0 0.2 • A data base of ~ 50,000 operating points is calculated with 0-D code • Engineering constraints are imposed to generate the operational boundaries shown below • Potential operating points are examined in more detail-PEST, TSC, etc

  13. Q = 5 FIRE AT Mode Operating Range is Limited by Nuclear Heating of Vac Vessel & First Wall Not by Cu Coils Nominal operating point • Q = 5 • Pf = 150 MW, • Pf/Vp = 5.5 MWm-3 (ARIES) • ≈ steady-state 4 to 5 tCR Physics basis improving (ITPA) • required confinement H factor and bN attained transiently • C-Mod LHCD experiments will be very important First Wall is the main limit • Improve cooling • revisit FW design Opportunity for additional improvement (optimization).

  14. “Steady-State” High-b Advanced Tokamak Discharge on FIRE Pf/V = 5.5 MWm-3 Gn ≈ 2 MWm-2 B = 6.5T bN = 4.1, bt = 5% fbs = 77% 100% non-inductive Q ≈ 5 H98 = 1.7 n/nGW = 0.85 Flat top Duration = 48 tE = 10 tHe = 4 tcr FT/P7-23

  15. Cool 1st Wall OFHC TF (≤ 7 T) Additional Opportunities to Optimize FIRE for the Study of ARIES AT Physics and Plasma Technologies ARIES AT (bN ≈ 5.4, fbs ≈ 90%) 12

  16. FIRE-AT Approaches the Parameters Envisioned for ARIES-Power Plant Plasmas

  17. Concluding Remarks • FIRE is very close to the optimum aspect ratio and size for an inductively-driven H-Mode burning plasma experiment using LN-cooled coils. • The present FIRE configuration is also capable of producing AT plasmas with characteristics approaching those of ARIES-RS with pulse lengths sufficient to study High-b Steady-state burning plasmas with fusion power densities of ≈ 5 MW m-3. • The present FIRE AT regimes are limited by the first wall and vacuum vessel and not the TF coil. - improve FW and Vac Vessel cooling ––> 6 tCR - change TF conductor to OFHC (Bt ≤ 7T) ––> ≈ 12 tCR • A bottoms up optimization of a FIRE for AT operation only has not been done, but the present case must be fairly close to the optimum.

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