Overcoming Mechanical and Economic Barriers in Alternative Fusion Reactor Designs: A Quantitative Engineering Framework

Abstract

Magnetized Target Fusion (MTF) using liquid-metal piston compression is often presented asa lower-cost alternative to steady-state magnetic confinement. This paper examines four ofits principal engineering-economic barriers with an explicit, reproducible parameter set: me-chanical fatigue of the piston array, sub-microsecond firing synchronisation, high-temperaturesuperconductor (HTS) tape cost, and Energy Return on Investment (EROI). Three findingsdiffer from the conventional framing. First, when the impact stress is bounded correctlythe fatigue problem is not a materials-selection problem but an impact rise-time controlproblem: provided the rise time exceeds ∼ 0.25 ms, both AISI 4340 steel and Ti-6Al-4Voperate below their endurance limits, and the real case for titanium rests on parasitic drivepower (∼0.9 MW saved, worth ∼ $0.5M/yr) rather than on fatigue life. Second, the widelyquoted 1 μs jitter target can be derived from convergence-symmetry requirements and carriesroughly an order of magnitude of margin; the binding constraint is the stochastic componentof hydraulic valve response, which machine learning cannot remove. Third, a corrected EROIcalculation using electrical rather than thermal output yields EROI ≈ 4.8 for a first-of-a-kind plant at a 2% recirculating power fraction, falling to ≈2.6 at a more realistic 20%. Asensitivity map is provided. We conclude that the barriers to commercial MTF are indeedengineering-economic rather than scientific, but that the economic margin is considerablythinner than commonly asserted, and that the fusion–space "self-financing loop" should betreated as a hypothesis requiring its own energy accounting rather than as a result