Analysis of the neutron kinematic end points from cryogenic DT inertial confinement fusion implosions using a model-independent technique*

Interpretation of the compressed fuel and low-mode asymmetries is a necessary metric for diagnosing implosion performance in inertial confinement fusion (ICF) experiments. One approach to evaluating ignition-relevant experiments is to calculate the areal density from fits of the deuterium backscatter (nD) and tritium backscatter (nT) kinematic edges that appear in the measured spectrum due to neutrons elastically scattering off of the compressed fuel.[1]  Analysis of the edges and the broader energy spectrum from 1-8 MeV, which are measured using high-resolution, high-dynamic range neutron time-of-flight (nTOF) spectrometers,[2] provides insight into the low-mode asymmetries affecting implosion performance.  The work presented here employs a variable P-spline technique to fit the nTOF spectrum by using a series of basis splines and a penalty term to minimize over-fitting of the signal.  Once the model independent neutron energy spectrum is extracted, the areal density and asymmetry are inferred using a theoretical model fit that considers several implosion factors and physical effects that influence the shape of the kinematic edges.

[1] A. J. Crilly et al., Phys. Plasmas. 27, 012701 (2020).

[2] C. J. Forrest et al., Rev. Sci. Instrum. 83, 10D919 (2012).