In the 1970′s, scientists began experimenting with powerful laser beams to compress and heat hydrogen isotopes to the point of fusion. This technique, called inertial confinement fusion, relies on the inertia of the plasma’s mass, rather than magnetic fields, for heating and confinement.
Scientists in the U.S. have made tremendous progress in ICF. The most notable of these projects is at Lawrence Livermore National Laboratory’s National Ignition Facility. The National Ignition Facility (NIF) is the world’s largest laser. NIF’s 192 intense laser beams will replicate the extreme conditions needed to achieve not only fusion ignition and burn, but also energy gain – two key milestones in the scientific pursuit of fusion energy as a source of electricity.
In NIF’s indirect drive approach, the lasers heat the inner walls of a gold cavity called a hohlraum containing the pellet, creating superhot plasma which radiates a uniform “bath” of soft X-rays. The X-rays rapidly heat the outer surface of the fuel pellet, causing a high-speed ablation, or “blowoff,” of the surface material and imploding the fuel capsule in the same way as if it had been hit with the lasers directly. Symmetrically compressing the capsule with radiation forms a central “hot spot” where fusion processes set in – the plasma ignites and the compressed fuel burns before it can disassemble.
The direct drive method focuses powerful beams of laser light on a small spherical pellet containing deuterium and tritium. The rapid heating caused by the laser “driver” makes the outer layer of the target explode, while the remaining portion of the target is driven inwards, compressing and further heating the fuel pellet. The resulting self-sustaining burn is known as ignition. Much of the research in the U.S. on direct drive fusion is being led by the Naval Research Lab.
To read ASP’s fact sheet on the National Ignition Facility, click here.