Direct Measurement of Energetic Electrons Coupling to an Imploding Low-Adiabat Inertial Confinement Fusion Capsule

We have imaged hard x-ray (> 100 keV) bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. We measure 570 J in electrons with E> 100 keV impinging on the fusion capsule under ignition drive conditions. This translates into an acceptable increase in the adiabat alpha, defined as the ratio of total deuterium-tritium fuel pressure to Fermi pressure, of 3.5%. The hard x-ray observables are consistent with detailed radiative-hydrodynamics simulations, including the sourcing and transport of these high energy electrons.