Determining X-ray conversion efficiency of direct drive implosions using Cubic Spline Unfolds of the Dante diagnostic

Broadband x-ray emission from direct drive inertial confinement fusion (ICF) implosions can be used to infer the total x-ray flux that is converted from the drive lasers as a function of time. A spectrally integrated soft x-ray diode array known as Dante records the flux of x-rays in specific photon energy bands by using a combination of grazing incidence mirrors, K-edge filters, and x-ray diodes. The voltage of the diodes is convolved with the response functions of the diodes, mirrors, and filters and can be directly inverted by assuming a cubic spline shape to the x-ray flux curve where the knot points of the spline coincide with the K-edges of each filtered channel [Soft x-ray spectrum unfold of K-edge filtered x-ray diode arrays using cubic splines, Review of Scientific Instruments 91, 073102 (2020)]. The analysis is done with the publicly available code Fiducia (https://pypi.org/project/fiducia/). Fiducia gives the time-resolved x-ray flux for both symmetric direct drive implosions at the OMEGA laser facility, and polar direct drive implosions at the National Ignition Facility (NIF). The time evolution of important x-ray photon energy bands is discussed.