We have imaged hard x-ray ($>100\mathrm{keV}$) 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 $E>100\mathrm{keV}$ 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.

• Received 26 November 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.135006