Early time hot electron generation and deposition at the capsule in indirect drive ICF implosions on the National Ignition Facility*

In indirect drive ICF experiments [1] on the National Ignition Facility (NIF), hot electrons generated by laser plasma instabilities can preheat the deuterium-tritium (DT) capsule, compromising ignition. While below detection limit, the early time (picket) allowable hot electrons in low adiabat implosions [1] are $\sim$ 1J in electrons with \textgreater 170 keV energy compared to 1000 J during the late time peak laser power [2]. At the same time, High Foot implosions [3] that demonstrated fuel-ablator mix mitigation and improved yield, have also shown picket hot electrons that can be comparable to allowable threshold. High Foot Re-emit experiments for tuning the picket radiation symmetry also infer the fraction and uniformity of hot electrons reaching the capsule by hard x-ray (50 keV) imaging combined with 40-300 keV spectra [2]. Their scalings with laser and plasma conditions are discussed. \\[4pt] [1] M. J. Edwards et al, \textit{Phys.} \textit{Plasmas} \textbf{20}, 070501 (2013).\\[0pt] [2] E.L. Dewald, \textit{et. al.,} \textit{Rev. Sci. Instrum.} \textbf{81}, 10D938 (2010).\\[0pt] [3] O. Hurricane, \textit{et. al,} \textit{Nature} \textbf{506, }343 (2014).