Improved Performance of High Areal Density Indirect Drive Implosions at the National Ignition Facility using a Four-Shock Adiabat Shaped Drive

Hydrodynamic instabilities can cause capsule defects and other perturbations to grow and degrade implosion performance in ignition experiments at the National Ignition Facility (NIF). Here, we show the first experimental demonstration that a strong unsupported first shock in indirect drive implosions at the NIF reduces ablation front instability growth leading to a 3 to 10 times higher yield with fuel $\rho R>1\mathrm{g}/{\mathrm{cm}}^2$. This work shows the importance of ablation front instability growth during the National Ignition Campaign and may provide a path to improved performance at the high compression necessary for ignition.

Figure 1

(a) Laser pulse shape for the low adiabat or low foot (blue curve), the high adiabat or high foot (red), and the adiabat shaped (purple) drives. The high-power feature for the first $\sim 3\mathrm{ns}$ is called the picket, and the trough is the following segment at low power. Features following the trough launch additional shocks, three shocks total for HF, and four shocks total for AS and LF. (b) Ablation front growth factors for the LF (blue), AS (purple), and HF (red) simulated using the code hydra [22].

Figure 2

(a)–(c) Neutron images obtained using the Neutron Imaging System [47] of (a) AS shot N141123, (b) LF N120321, and (c) HF N130812.

Figure 3

Total neutron yield plotted as a function of fuel $\rho R$ for the AS, HF, and LF implosions. The dashed curves are contours of calculated yield amplification from hot spot alpha self-heating. The AS achieved significantly higher yield than the LF platform at comparable $\rho R$.

Figure 4

(a) Total neutron yield plotted as a function of inferred CH mix mass. (b) Inferred hot spot density as a function of measured DT ion temperature. Plotted also are contours of inferred hot spot pressure. AS shot N141123 achieved considerable hot spot density and pressure compared to the comparable velocity LF and HF companions.