Diagnosing alpha-heating through MRS measurements of the alpha-knock-on tail at the NIF and the need for the next-generation MRS*

In an Inertial Confinement Fusion (ICF) implosion, fast alpha particles transfer part of their energy to the D and T fuel ions, and when these energetic D or T react with thermal ions, they generate an alpha knock-on (AKN) component in the ICF neutron spectrum. The relative magnitude of the AKN component relative to the primary yield provides a direct assessment of alpha heating of the fuel ions. Using the Magnetic Recoil Spectrometer (MRS) on the NIF, measurements of the AKN spectra have provided information about the alpha heating, quality of burn propagation, and extent of mix. Since more accurate measurement of alpha heating is essential, the next-generation Magnetic Recoil Spectrometer (MRSnext) is being designed to replace the current MRS for measurements of the neutron spectrum at the NIF to unparalleled accuracy. The MRSnext will provide far-superior performance and faster data turnaround than the current MRS, i.e., a 2× and 6× improvement in energy resolution on the NIF and OMEGA, respectively, and 20× improvement in data turnaround time. The improved performance is enabled by using electromagnets that provide a short focal plane and unprecedented flexibility.