Fast Ignition Proposed for Inertial Confinement Fusion

Two groups have independently reported fast-ignition techniques for inertial confinement fusion, which drives the implosion of capsules of deuterium and tritium with laser or ion beams, either directly or with x-rays produced in a target hohlraum. Fast ignition uses a precompressed target to lower the energy requirements on the ignition pulses.

In the Jan. 15 issue of Physical Review Letters, an international team of researchers working with the Petawatt laser at Lawrence Livermore National Laboratory in Livermore, Calif., describe how energetic protons produced in the laser ionization of target foils can serve as the ignition spark. They targeted 100-µm-thick gold and plastic foils with 600-J, 0.5-ps pulses of infrared light from Petawatt, yielding up to 10¹³ protons in a 30-J beam within a few hundred microns of the target.

Researchers at Darmstadt University of Technology in Germany have simulated the effects of depositing laser energy on the corona of a target. Reporting in the Feb. 5 issue of Physical Review Letters, they suggest that the pulse forms a burn wave that propagates through the fuel pellet, reducing the required ignition energy to 10 kJ, or even to 3 to 5 kJ if there is no ballistic transport in the core.