Anomalous enhancements of low-energy fusion rates in plasmas: the role of ion momentum distributions and inhomogeneous screening

TL;DR

This paper investigates how non-thermal ion momentum distributions and inhomogeneous screening effects can explain unexpectedly high low-energy fusion rates observed in plasmas, challenging existing models.

Contribution

It introduces the roles of quantum uncertainty and spatial screening fluctuations in enhancing fusion rates, providing a new perspective on plasma reaction dynamics.

Findings

Quantum uncertainty broadens ion momentum distributions, increasing reaction rates.

Spatial fluctuations in screening radius further enhance low-energy fusion.

Enhanced models better match experimental observations.

Abstract

Non-resonant fusion cross-sections significantly higher than corresponding theoretical predictions are observed in low-energy experiments with deuterated matrix target. Models based on thermal effects, electron screening, or quantum-effect dispersion relations have been proposed to explain these anomalous results: none of them appears to satisfactory reproduce the experiments. Velocity distributions are fundamental for the reaction rates and deviations from the Maxwellian limit could play a central role in explaining the enhancement. We examine two effects: an increase of the tail of the target Deuteron momentum distribution due to the Galitskii-Yakimets quantum uncertainty effect, which broadens the energy-momentum relation; and spatial fluctuations of the Debye-H\"{u}ckel radius leading to an effective increase of electron screening. Either effect leads to larger reaction rates especially large at energies below a few keV, reducing the discrepancy between observations and theoretical expectations.