Electron Shock Ignition of Inertial Fusion Targets

It is shown that inertial confinement fusion targets designed with low implosion velocities can be shock-ignited using laser-plasma interaction generated hot electrons (hot-$e$’s) to obtain high energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-$e$’s which can be produced only at a large laser facility like the National Ignition Facility, with the laser-to-hot-$e$ conversion efficiency greater than 10% at laser intensities $\sim {10}^{16}\mathrm{W}/{\mathrm{cm}}^2$.

Figure 1

Sketch of the electron shock ignition scheme (a) and planar model cited from Ref. [18] (b). In Ref. [18], the initial hot spot and shell density are uniform, and the isobaric initial condition is used. Here the initial conditions are taken from LILAC simulations.

Figure 2

(a) Target and (b) laser pulse with (solid line) and without (dashed line) the shock power spike.

Figure 3

(a) Time-dependent laser-to-hot-$e$ conversion efficiencies from PIC simulations. The time-integrated laser-to-hot-$e$ conversion efficiency above 50 keV is ${\eta }_{50}\sim 25\%$ and above 25 keV is ${\eta }_{25}\sim 31\%$. (b) The hot-spot pressure ratio $R=P_{\text{hot}\text{−}e}/P_{\text{laser}}$ versus the launching time. $P_{\text{hot}\text{−}e}$ and $P_{\text{laser}}$ are the hot-spot pressures at stagnation driven by the hot-$e$’s and laser.

Figure 4

(a) Density (dotted line) and pressures with hot-$e$’s (solid line) and without hot-$e$’s (dashed line). The launching time is 10.3 ns with a hot-$e$ energy of 25 kJ. (b) Gain versus launching time for a hot-$e$ pulse with various energies.

Figure 5

(a) Energy gain versus ${\mathrm{YOC}}_{\text{no}\alpha }$ at 10.3 and 10.5 ns with different initial roughness conditions. (b) Density plot at the peak neutron rate with $\alpha$ heating and gain $\sim 4$ at 10.3 ns. (c) Corresponding density plot to Fig. 4 without $\alpha$ heating. The hot-$e$ energy is 25 kJ.