Novel Target Designs to Mitigate Hydrodynamic Instabilities Growth in Inertial Confinement Fusion

High density carbon (HDC) ablator is one of the promising candidates toward thermonuclear ignition in inertial confinement fusion (ICF), but it shows the largest ablation front instability growth as compared to other traditional ablator materials. In this Letter, we propose a novel HDC-CH capsule design, opening the way to mitigate the hydrodynamic instabilities by using CH as the outermost ablator layer, while keeping HDC as the main ablator for maintaining the advantage of short laser pulses. The CH layer is completely ablated during the shock transit phase. In the HDC-CH design, it is the first shock reflected from the HDC/CH interface that meets the ablation front first, which reduces the ablation front growth factor by about one order of magnitude at peak implosion velocity due to the Richtmyer-Meshkov and the Rayleigh-Taylor instabilities. Our 2D simulation studies demonstrate convincingly that the ablation front growth factor of the HDC-CH capsule can be significantly reduced at both the end of shock transit phase and the time at peak implosion velocity, as compared to a HDC capsule. This novel HDC-CH capsule not only keeps the main advantage of the HDC ablator, but also has the advantage of low hydrodynamic instabilities, which can provide a larger margin toward ICF ignition. It can be applicable to both indirect-drive and direct-drive targets.

Figure 1

Schematics of HDC-CH capsule (left) and HDC capsule (middle), together with their radiation drives (right).

Figure 2

Plots of the logarithmic radial derivative of hydrodynamic pressure in Lagrangian coordinate vs time space for HDC-CH capsule (upper) and HDC capsule (lower). The yellow dashed lines mark the locations of interfaces of DT ice-gas, HDC/DT and HDC/CH (or doped-undoped in HDC capsule), respectively, and the red lines denote the trajectory of ablation front. The time place of $t_{\mathrm{DT}}$ is marked by the white arrow lines.

Figure 3

Comparisons of temporal evolution of the ablation front linear growth factor during shock transit phase between the HDC-CH capsule (red) and the HDC capsule (black) for modes $L=24$ (thick line) and $L=64$ (thin line). The yellow and gray lines denote the place of $t_{\mathrm{DT}}$ in HDC-CH capsule and HDC capsule, respectively.

Figure 4

Density contours for modes $L=24$ and $L=64$ in Lagrangian coordinate vs angle space of HDC capsule (a) and HDC-CH capsule [(b) and (c)] at a short time before $t_{\mathrm{DT}}$. Notice that (c) presents the range of 922 to $935\mu \mathrm{m}$ of (b). The black line in (a) denotes the doped-undoped interface of HDC capsule and in (b) denotes the position of HDC/CH interface of HDC-CH capsule. The white lines in (c) are the density contours to show the negative perturbations of HDC-CH capsule, and the range between 922 and $925\mu \mathrm{m}$ is the inverse-phase region of HDC-CH capsule at this time.

Figure 5

Comparisons of ablation front linear GF (thick lines) and DT/HDC interface linear GF (thin lines) between HDC capsule (black lines) and HDC-CH capsule (red lines) at $t_{\mathrm{DT}}$ (a) and at peak implosion velocity (b), with perturbations initially seeded on the ablator outer surface.