Measurements of Non-Maxwellian Electron Distribution Functions During the Ablation Phase of Inertial Confinement Fusion Implosions

Patrick Adrian, Massachusetts Institute of Technology

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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 electrons1. The modification to the distribution function affects electron transport and heat conduction which are critical to model correctly in ICF. To study this problem, we have conducted implosion experiments at the OMEGA laser facility where thin glass spherical targets were imploded with 9 kJ of energy in a 1 ns pulse. The primary measurement which shows evidence for non-Maxwellian electrons during laser ablation was the x-ray emission history in multiple energy bands. The emission history is sensitive to the shape of the distribution function. This work displays our measurements as well as calculations of the x-ray emission using a variety of electron distribution functions. Our results show that the distribution function which produces model emission consistent with the measurements is the Langdon distribution.

1B. A. Langdon PRL (1980).

Abstract Author(s): P. J. Adrian, M. Gatu Johnson, N. V. Kabadi, C. K. Li, R. D. Petrasso, S. P. Regan, F. H. Seguin, G. D. Sutcliffe, and J. A. Frenje