Studies of non-Maxwellian electron distributions in the coronal plasma of inertial confinement fusion implosions

Laser ablation of materials is mediated through inverse Bremsstrahlung heating, which converts laser energy into plasma thermal energy, and is an important process for Inertial Confinement Fusion (ICF). Inverse Bremsstrahlung heating has been predicted to modify the electron distribution function through preferentially heating slow-moving electrons [B. A. Langdon PRL (1980)]. The modification to the distribution function affects the electron transport and heat conduction, which are critical to model correctly in the context of ICF. To study this physics, we have conducted a set of implosion experiments at OMEGA where thin-glass spherical targets were imploded with 9 kJ of energy in a 1-ns pulse. Measurement of the x-ray emission history in multiple energy bands provided the primary data, which shows evidence for non-Maxwellian electron distributions in the coronal plasma. The reason for this is that the emission history is sensitive to the shape of the electron distribution function. The interpretation of the data is aided by simulations of the x-ray emission using a variety of electron distribution functions. The results show the electron distribution function is best described by the Langdon distribution. This work is supported by the DOE, the MIT/NNSA CoE and NLUF