Energy security

Giant lasers pass new milestone towards fusion energy

Physicists working at the National Ignition Facility (NIF) in the US say they have passed another important milestone in their quest for nuclear fusion energy. They have shown that the fusion energy generated by the laser implosion of a deuterium-tritium fuel capsule is twice that of the kinetic energy of the implosion. By further trebling the fusion energy, they say they will be close to the long-sought goal of an overall net energy gain.

The $3.5bn NIF trains 192 pulsed laser beams on to the inner surface of a centimetre-long hollow metal cylinder known as a hohlraum. Inside is a fuel capsule, which is a roughly 2 mm-diameter hollow sphere containing a thin deuterium-tritium layer. Each pulse lasts just a few nanoseconds and the lasers can deliver about 1.8 MJ of energy. This powerful blast causes the capsule to implode rapidly, creating immense temperatures and pressures inside a central “hot spot”, where fusion reactions occur.

The long-term goal is that the energy of neutrons given off by fusion can generate electricity. Before this is possible, NIF must show that it is possible to achieve ignition – the point at which fusion reactions generate at least as much energy delivered by the laser system. This involves self-sustaining reactions, in which the alpha particles that are also emitted during fusion give off enough heat to initiate further fusion.