Novel Hot-Spot Ignition Designs for Inertial Confinement Fusion with Liquid-Deuterium-Tritium Spheres

A new class of ignition designs is proposed for inertial confinement fusion experiments. These designs are based on the hot-spot ignition approach, but instead of a conventional target that is comprised of a spherical shell with a thin frozen deuterium-tritium (DT) layer, a liquid DT sphere inside a wetted-foam shell is used, and the lower-density central region and higher-density shell are created dynamically by appropriately shaping the laser pulse. These offer several advantages, including simplicity in target production (suitable for mass production for inertial fusion energy), absence of the fill tube (leading to a more-symmetric implosion), and lower sensitivity to both laser imprint and physics uncertainty in shock interaction with the ice-vapor interface. The design evolution starts by launching an $\sim 1$-Mbar shock into a DT sphere. After bouncing from the center, the reflected shock reaches the outer surface of the sphere and the shocked material starts to expand outward. Supporting ablation pressure ultimately stops such expansion and subsequently launches a shock toward the target center, compressing the ablator and fuel, and forming a shell. The shell is then accelerated and fuel is compressed by appropriately shaping the drive laser pulse, forming a hot spot using the conventional or shock ignition approaches. This Letter demonstrates the feasibility of the new concept using hydrodynamic simulations and discusses the advantages and disadvantages of the concept compared with more-traditional inertial confinement fusion designs.

Figure 1

Snapshots of density (solid lines) and pressure (dashed lines) profiles at (a) $t=35\mathrm{ns}$, (b) $t=51\mathrm{ns}$, and (c) $t=61\mathrm{ns}$. Green and blue lines denote CH and DT, respectfully.

Figure 2

Snapshots of density (solid lines) and pressure (dashed lines) profiles during the adjustment shock propagation (a) at $t=72\mathrm{ns}$ and (b) at $t=110\mathrm{ns}$ when shell velocity goes to zero.

Figure 3

Dynamically formed shell profiles [(a) linear and (b) logarithmic-density scales, respectively] at $t=180\mathrm{ns}$ for the pulse shown in Fig. 4.

Figure 4

Pulse shape for the $E_L=1.15$-MJ ignition dynamic-shell design. The inset shows the main drive pulse.

Figure 5

(a) Picket-pulse, dynamic-shell designs with the multiple pickets and (b) a picket and continuous drive options for the shock transit phase through a homogeneous fuel sphere.