generalfusion

Inertial confinement fusion is the second of two primary areas of fusion research. It involves imploding a small sphere of deuterium and tritium with such energy that the nuclei momentarily reach very high-density fusion conditions.

Inertial confinement fusion operating principle

Inertial confinement fusion works on the principle that directing an intense amount of energy, very quickly, at a small deuterium-tritium target can momentarily create fusion conditions before the fuel flies apart. In practice, this involves a small (~1 cm) spherical shell of plastic or glass filled with a deuterium-tritium gas mixture. Hundreds of intense lasers are fired all around the sphere, exploding the outside of the shell. The rest of the shell is accelerated inwards due to the opposite inertial reaction of this explosion and compresses and heats the gas mixture to thermonuclear conditions. The inertia of the imploding material alone keeps the plasma together for the short time (picoseconds) during which fusion occurs. Since the hot plasma exists for only a very short time, it must be very dense (1,000 times as dense as a solid) to produce enough fusion reactions to make more energy than that expended by the lasers.

The challenges surrounding inertial confinement fusion involve the magnitude of the energy that must be stored and delivered onto the very small target, and the time it takes to store the energy and replace the target between each pulse. To be economically practical, a further challenge is that the amount of electricity produced with each impulse has to be much more valuable than the cost of the consumables (targets).

Existing inertial confinement fusion machines

Key inertial confinement fusion projects include:

• National Ignition Facility (NIF), USA [lasers.llnl.gov]
The US leads the development of inertial confinement fusion. Their 1.8 MJ National Ignition Facility at Lawrence Livermore National Laboratory is the largest laser facility in the world, and focuses 192 laser beams onto a pea-sized target. They began firing their lasers onto the target in June 2009, and in February 2010 delivered an unprecedented 1 MJ of energy within a few billionths of a second. This is about 30 times the energy ever delivered by any other group of lasers in the world, and for a fraction of a second represents about 500 times the power used by the entire United States. This energy burst is sufficient to induce thermonuclear conditions, and the facility will attempt to fuse a pellet of deuterium and tritium in 2011 or 2012. If successful, it will produce more fusion energy than the laser energy it consumes, and thereby set the new world record for contained fusion energy. However, the facility as a whole will still draw more power than it generates due to the low efficiency of converting electrical energy into laser energy.

• Laser Mégajoule (LMJ), France [www.lmj.cea.fr]
France is building a similar facility to NIF known as Laser Mégajoule, expected to be complete in 2012.

• High Power Laser Energy Research Facility (HiPER), European Union (proposed) [www.hiper-laser.org]
If built, the HiPER facility would begin operation in the 2020s and would use about 3 MJ of electrical power to generate 30 MJ of fusion power. This would be the first inertial confinement fusion machine to demonstrate true net gain including the electrical energy needed to charge the lasers.