Description
Time-resolved neutron measurements provide critical insight into the dynamics of inertial confinement fusion (ICF) implosions, enabling discrimination between igniting and non-igniting plasmas and helping to diagnose the origins of shot-to-shot performance variability. However, accessing temporal information from neutron diagnostics typically requires complex or detector-intensive approaches that have not yet been successfully implemented.
We present and validate a moments-method framework that enables the extraction of time-dependent neutron source information using only a small number of neutron time-of-flight (nTOF) detectors at different distances from the target. For example, as few as four detectors are sufficient to recover the burn-averaged rate of change of the ion temperature. The method provides a tool for measuring the shape of the DD and DT neutron spectral peaks by taking central moments of the peaks and relating these moments to the time-dependent behaviour of the reacting ion distribution functions.
The method is first assessed using controlled toy models to verify its underlying assumptions and mathematical structure. It is then applied to realistic simulation datasets incorporating time-dependent ion temperature evolution and hydrodynamic burn dynamics.
These results demonstrate that the moments method provides a robust and experimentally accessible route to inferring key dynamical quantities—such as burn-averaged rates of change of ion temperature and fluid velocity—using existing nTOF diagnostics, significantly extending their time-resolved diagnostic capability.