Characterization of density and metal content in low density foam targets for inertial confinement fusion

Abstract

Targets for Inertial Confinement Fusion (ICF) experiments to measure isoelectronic temperatures achieved in open configurations have been manufactured from low density polymethylpentene. The temperature measurements are made by ratioing the intensity of two nearby X-ray lines, in this case from titanium and chromium. This required these metals to be added to the foams during manufacture. Individual targets consisted of machined cylinders of foam 2 mm in diameter by 2 mm long. Because of small scale variability in the foam, it was necessary to individually characterize each target for metal content and density to determine the total mass of plastic and metal present to allow a correct calculation of the temperature to be made. The requested density of the foam was less than 5 mg/cm 3 and the metal loading was to be 0.5 wt.% each of titanium and chromium. This means the mass of plastic was roughly 10 μg and the metal mass was roughly 50 ng. This low level of material to be detected required the application and modification of X-ray fluorescence and beta particle transmission methods to characterize the foams.