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

Magnetized Target Fusion (MTF) with liquid-metal piston compression and related pulsedconcepts are frequently proposed as lower-capital alternatives to the steady-state tokamakparadigm. Their practical realization, however, is limited by four coupled engineering-economic barriers: high-cycle mechanical fatigue of the compression drivers, sub-microsecondsynchronization of large piston arrays, the unit cost of high-temperature superconductor(HTS) tape, and the net energy balance of the plant. This paper develops a transparent,fully reproducible quantitative framework for each barrier. (i) Using an impulse–momentumstress estimate (σpeak = 24 MPa) combined with a Basquin stress–life model and a fatiguenotch factor Kf = 3, we show that both AISI 4340 and Ti-6Al-4V exceed the required6.3 × 108 lifetime cycles by more than four orders of magnitude, with Ti-6Al-4V offering a7.9× larger life margin for an incremental material cost of only $114,000 per 3000 kg pistonset; we therefore argue that fatigue is not the binding constraint, and that corrosion–erosionin Pb–Li is the governing degradation mode. (ii) We derive a root-sum-square timing bud-get yielding 0.51 μs RMS jitter and report a reproducible synthetic-data study in which afeed-forward predictive controller reduces array jitter from 8.29 μs to 1.27 μs; reaching the1 μs target additionally requires reduction of the stochastic actuator noise floor, which wequantify. (iii) A learning-curve model with an explicit sensitivity analysis projects REBCOtape costs falling from $400/m to $25–90/m. (iv) A corrected Energy Return on Investment(EROI) analysis for a 1 GWth plant gives EROIel ≈ 4.8 (electrical basis) and EROIth ≈ 11.6(thermal basis), with an energy payback period of 5.8 years — values that supersede figuresreported in earlier drafts of this framework. We conclude that the dominant remaining ob-stacles are engineering-economic rather than scientific, while explicitly delimiting which ofour claims are established, projected, or speculative.