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Inertial confinement fusion uses lasers to rapidly compress and heat a small pellet containing deuterium and tritium to induce nuclear fusion. The goal is to achieve ignition and produce more energy than consumed, but technical challenges remain. A new approach called rapid ignition has been proposed but not yet tested.
Inertial confinement fusion (ICF) is a method of achieving nuclear fusion by rapidly compressing and heating a material. This process is usually done with high power lasers, all of which are focused on a small pellet to heat it up quickly. The intense heating vaporizes the material within the pellet, creating a shock wave that is hot and dense enough to cause the material to melt. Although inertially confined fusion has yet to produce more useful energy than it consumes, research into how to build a commercially viable energy source is still ongoing.
The basic ingredients of an inertially confined fusion pellet are deuterium and tritium, both isotopes of hydrogen. The fusion reaction between deuterium and tritium is much easier to achieve than any other reaction, so an energy-producing deuterium/tritium reactor is the primary goal of modern fusion research. These pellets are very small, weighing much less than an ounce, and are fed one at a time into the inertially confined fusion reactor.
Once the pellet is loaded, very large lasers are used to rapidly heat the pellet to melting temperature, at millions of degrees Fahrenheit (Celsius). The rapid heating of the outer layer of the pellet causes it to vaporize and expand rapidly, exerting pressure on the inside of the pellet. If the lasers deliver enough energy, the pellet’s interior will be compressed quickly enough to induce nuclear fusion, which in turn will make the pellet hotter. This condition is called “ignition” and is the goal of most modern inertial confinement fusion experiments.
The main difficulty with inertial confinement fusion is providing enough energy to the pellet to heat it to the melting temperature before the pellet is dispersed into space. To produce energy from fusion, the reaction must pass a value called the Lawson criterion, which gives the minimum confinement time needed for a given volume of fuel. This requires passing many megajoules of energy through the laser system in a few microseconds; doing it reliably, without consuming too much energy, presents an enormous technical challenge. A new approach to the confinement problem called ‘rapid ignition’ has been proposed, where a single rapid laser flash ignites the pellet after it has already been compressed. While this approach sounds promising in theory, it has not yet been successfully tested.
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