Exploring the fusion power plant design space: comparative analysis of positive and negative triangularity tokamaks through optimization

The optimal triangularity for fusion power plants depends on navigating fundamentally different operational constraints rather than achieving specific plasma performance. We present the first systematic comparison of positive (PT) and negative triangularity (NT) configurations using constrained multi-objective optimization with FUSE, evaluating >200,000 integrated designs minimizing capital cost while maximizing operational reliability (q₉₅) under engineering constraints (250±50MW net electric, TBR>1.1, 1hr flattop).

Both configurations achieve cost parity through contrasting strategies. PT designs, constrained by the narrow window between L-H threshold requirements and power exhaust limits (Psol/R P_sol​/R<15MW/m), optimize via larger machines (R₀​>6.5m) with reduced field (~8T). Despite resilience to 40% pedestal degradation, PT's viability critically depends on L-H threshold uncertainties where 50% variations could eliminate the design space.

NT exploits immunity to H-mode constraints, accessing compact high-field designs (R₀​~5.5m, B_0​>12T) with natural HTS synergy. While NT's radiative edge doubles auxiliary power requirements (200-250MW vs 80-120MW) it provides inherent exhaust handling without operational limits.

Key finding: power exhaust instead of confinement represents the primary optimization bottleneck. This suggests risk-informed configuration selection: PT for near-term demonstrations with predictable constraints, NT for commercial plants prioritizing operational robustness across uncertain reactor-scale extrapolations.