Dynamically assisted nuclear fusion in the strong-field regime

We consider quantum tunneling between fusing nuclei in the presence of a harmonically time-varying field. The tunneling rate is calculated using Floquet/Volkov (FV) and Kramers-Henneberger (KH) approaches, which are both compared to a first-principles numerical solution of the Crank-Nicolson (CN) type. Numerical validation of the FV approach justifies its use in analytical estimates of laser-enhanced reaction rates, while the KH approach does not reproduce the predictions of the others. For a deuterium-tritium plasma at a temperature of 1 keV, it is found that significant enhancement of fusion reactivity requires field strengths on the order of 10¹⁵--10¹⁶ V/m and photon energies below 1 keV, which is within reach of next-generation x-ray free electron lasers (XFELs).