Shock Ignition of Thermonuclear Fuel with High Areal Density

A novel method by C. Zhou and R. Betti [Bull. Am. Phys. Soc. 50, 140 (2005)] to assemble and ignite thermonuclear fuel is presented. Massive cryogenic shells are first imploded by direct laser light with a low implosion velocity and on a low adiabat leading to fuel assemblies with large areal densities. The assembled fuel is ignited from a central hot spot heated by the collision of a spherically convergent ignitor shock and the return shock. The resulting fuel assembly features a hot-spot pressure greater than the surrounding dense fuel pressure. Such a nonisobaric assembly requires a lower energy threshold for ignition than the conventional isobaric one. The ignitor shock can be launched by a spike in the laser power or by particle beams. The thermonuclear gain can be significantly larger than in conventional isobaric ignition for equal driver energy.

Figure 1

Sketch of a uniform pressure isobaric assembly (dashed line) and of a nonisobaric assembly with the pressure peak inside the hot spot (solid line). The gray shaded region is the density profile.

Figure 2

Pressure (solid line) and density (dashed line) profiles of a plasma slab hitting a rigid wall. Part (a) shows the initial profiles. Part (b) shows the profiles at peak compression.

Figure 3

Pressure (solid line) and density (dashed line) profiles for the plasma slab before (a) and after (b) the shocks’ collision.

Figure 4

Wetted-foam target (a) and 290 kJ UV-laser pulse (b) with (solid line) and without (dashed line) the shock power spike.

Figure 5

Pressure (solid line) and density (dashed line) profiles at peak compression for the 290 kJ pulse shapes with and without ignitor shock.