Influence of laser induced hot electrons on the threshold for shock ignition of fusion reactions

Abstract

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Shock generation comparison with planar and hemispherical targets in shock ignition relevant experiment

“…However, the SBS threshold is below the SRS one, around 2 to 5x10 14 W/cm 2 , that qualitatively explain the SBS prevalence over SRS, in agreement with the data. Comparing now these thresholds in plasma profiles expected from targets designed for the direct-drive scheme for LMJ [28], we note that the electron density scalelength is typically one-third smaller in our experiments, thus the SRS threshold is expected to be one third lower as well for LMJ. On the contrary, both the electron temperature T e and the expansion velocity scale-length L V = [1/V ΔV/Δz] -1 increase by a factor of two in the LMJ design, as calculated by the CHIC code.…”

The role of hot electrons in the dynamics of a laser-driven strong converging shock

“…The CHIC simulations show only a minor increase in ablation pressure (less than 10%) and a strong increase in shock pressure resulting from hot electrons. The target preheat is an undesirable issue in the context of shock ignition since a shock of a small strength is much less ecient in the fuel heating of the central spot and hot-electron preheat during the ignitor spike may lead to hot-spot mass increase because of inner-shell ablation [28]. These problems may be mitigated by designing a target with a larger areal density.…”

Confirmation of hot electron preheat with a Cu foam sphere on GEKKO-LFEX laser facility

“…6(b). Although the hot electron preheat could increase the shock pressure, it also decreases the shock strength by raising the local sound velocity; 15,17 consequently, a smaller peak areal density (0:191 g=cm 2 ) is achieved compared with that (0:238 g=cm 2 ) in the case without preheat (see Fig. 7), corresponding to a decrease by 19.8% (or 0:047 g=cm 2 ).…”

“…hcos hi is the angular moments of the hot electron distribution function, which is introduced due to the scattering effect. 16 Generally, the LPI produced hot electrons have a large initial divergence angle, 11,15,17 which means that they deposit more quickly along the target radius than a wellcollimated electron beam does. To take into account this quick energy deposition, we introduce a parameter, g SP (>1), in our model.…”