Neutron Generation by Laser-Driven Spherically Convergent Plasma Fusion.

We investigate a new laser-driven spherically convergent plasma fusion scheme (SCPF) that can produce thermonuclear neutrons stably and efficiently. In the SCPF scheme, laser beams of nanosecond pulse duration and 10(14)-10(15) W/cm(2) intensity uniformly irradiate the fuel layer lined inside a spherical hohlraum. The fuel layer is ablated and heated to expand inwards. Eventually, the hot fuel plasmas converge, collide, merge, and stagnate at the central region, converting most of their kinetic energy to internal energy, forming a thermonuclear fusion fireball. With the assumptions of steady ablation and adiabatic expansion, we theoretically predict the neutron yield Y-n to be related to the laser energy E-L, the hohlraum radius R-h, and the pulse duration tau through a scaling law of Y-n alpha (E-L/R-h(1.2) tau(0.2))(2.5). We have done experiments at the ShengGuangIII-prototype facility to demonstrate the principle of the SCPF scheme. Some important implications are discussed.