Inference of the electron temperature in ICF implosions from the hard X–ray spectral continuum

Using the free-free continuum self-emission spectrum at photon energies above 15 keV is one of the most promising concepts for assessing the electron temperature in ICF experiments. However, these photons are due to suprathermal electrons whose mean-free-path is much larger than thermal, making their distribution deviate from Maxwellian in a finite-size hot-spot. The first study of the free-free X-ray emission from an ICF implosion is conducted with the kinetic modifications to the electron distribution accounted for. These modifications are found to result in qualitatively new features in the hard X-ray spectral continuum. Inference of the electron temperature as if the emitting electrons are Maxwellian is shown to give a lower value than the actual one.