Standard radiation damage models for fusion materials assume that reaction energy manifests exclusively as the kinetic energy of reaction products, thermalizing via Coulomb cascades. However, persistent anomalies—such as non-classical fast-ion distributions and anomalous ⟨100⟩ dislocation loops in tungsten—suggest that these models do not fully capture the primary damage state. Extending a mass-defect framework recently applied to fission environments, we propose that D+D fusion releases a pre-thermal transient pressure pulse (10–50 GPa, <1 ps) preceding kinetic thermalization. This athermal mechanical component would fundamentally reshape atomic cascade topologies, thereby systematically biasing displacement per atom (dpa) and defect recombination estimates. We propose a directly falsifiable XFEL experiment utilizing a mass-equivalent differential pair: ⁴⁸TiD₂ (fusion-active) versus ⁵⁰TiH₂ (inert control) at ≈52 amu. This selection renders baseline acoustic impedance and hydrodynamic responses indistinguishable, cleanly isolating fusion-specific signals. Laser-accelerated 3–5 MeV deuterons drive volumetric D+D fusion in freestanding single-crystal membranes, while time-resolved 50-fs XFEL diffraction monitors the sub-picosecond lattice response. The hypothesis predicts anomalous compressive Bragg broadening (Δd/d ≈ 3×10⁻² to 1.5×10⁻¹) exclusively in ⁴⁸TiD₂ within a <1 ps window—a regime preceding electron-phonon thermalization. Indistinguishable diffraction profiles at XFEL sensitivity (≈10⁻⁴) will cleanly falsify the hypothesis. Conversely, reproducible excess strain will mandate an upward revision of mechanical energy deposition in primary damage models. If confirmed, this pre-thermal mechanical partition would reframe primary damage calculations and fundamentally alter predictive frameworks for radiation-tolerant fusion material design.
Joseph George (Sat,) studied this question.