High Energy Density Physics (HEDP) experiments commonly exhibit large temporal and spatial

changes in conditions and present extreme environments in which to perform measurements.

Interpretation of experimental observations can therefore often rely on a simplified model of both

the measured object, e.g. Z-pinch, and the measurement species, e.g. X-rays. These models belie the

true complexity of the system and can miss additional information contained within measurements.

Synthetic diagnostics aim to numerically describe the behaviour of the measurement species with

similar accuracy as used to model the experiment. They both provide insight into the relationships

between measured and simulated conditions and highlight the important missing physics from

simplified analysis models.

In this talk nuclear diagnostics in Inertial Confinement Fusion (ICF) experiments will used as a case

study for synthetic diagnostics. Neutron spectroscopy and imaging are key techniques used in

diagnosing ICF experiments. High energy neutrons created in DT fusion reactions are commonly used

to infer the conditions of the fusing plasma. However, the neutrons can also undergo scattering

events within in the currently poorly measured dense cold fuel layer. By constructing detailed

neutron transport models, features of the scattered neutron spectrum can be modelled and used to

extract a wealth of information about the dense fuel layer. For example, the shape of the spectrum

produced by back scattering neutrons has been shown to depend on the fluid velocity and

temperature of the dense fuel. Additionally, these detailed neutron transport models can be used to

create data analysis techniques which more accurately describe the measured signals.