High-accuracy measurements of yield and areal density ($\rho $R) using the Magnetic Recoil Spectrometer (MRS) at the National Ignition Facility (NIF)

Proper assembly of capsule mass, as manifested through the evolution of \textit{$\rho $R}, is essential for achieving hot-spot ignition planned at the NIF. Experimental information about \textit{$\rho $R} and\textit{$\rho $R} asymmetries, ion temperature ($T_{i})$ and yield ($Y_{n})$ are therefore critical for understanding how the assembly of the fuel occurs. To obtain this information, a neutron spectrometer, called the MRS, was commissioned on the NIF in the fall of 2010 for measurements of the absolute neutron spectrum. From measured down-scattered ratios (\textit{dsr}) in the range 2.4-4.9{\%}, \textit{$\rho $}\textit{Rs} in the range 600-1300 mg/cm$^{2}$ have been inferred. The accuracy of these measurements was as good as 6{\%}, a value that will improve as $Y_{n}$ and \textit{dsr} increase. From measurements of the primary neutron spectrum, $Y_{n}$ has also been determined to an accuracy of 5{\%}. This work was supported in part by the U.S. DOE, LLNL and LLE.