Fusion Energy
Exploring alternatives to magnetic confinement Laser fusion, linear devices and advanced fuels By Aleksandra Peeva
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aser fusion is a method of igniting nuclear fusion reactions and is a potential alternative to magnetic confinement (see article, page 6). It does this through inertial confinement, using high-power lasers to heat and compress tiny spherical capsules containing fuel pellets made up of hydrogen isotopes such as deuterium and tritium. The intense heating of the capsule surface creates a micro-implosion of the fuel, and, as a result, the pellet’s surface layer is ablated and explodes. The inertia created by this process keeps the fuel confined for long enough for fusion reactions to take place. Experiments in the field of laser fusion began in the 1970s. Today, the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in the United States of America has 192 laser beams and is easily the world’s biggest laser facility. At NIF, lasers heat the inner walls of a cylindrical golden container, called a hohlraum, that holds the capsule containing the deuterium–tritium fuel pellet. The laser–hohlraum interaction generates X-rays, which heat up and compress the capsule, creating a central hot spot inside the pellet, where fusion reactions take place. To achieve ignition — the point at which fusion becomes completely self-sustaining — NIF’s capsules should release around 30 times more energy than they absorb.
8 | IAEA Bulletin, May 2021
“We have made significant progress at NIF over the past five years and are now able to produce two and a half to three times more energy than what we put into the hot spot of the fuel,” said Brian Spears, Deputy Lead for Modelling in Inertial Confinement Fusion at NIF. “Getting to the 30 times amplification gain is still a major goal, but this is a non-linear process and we have already taken many important technical steps to get there.” Increasing the central pressure inside the fuel hot spot to several billion times of atmospheric pressure is key to achieving commercially viable fusion. NIF has made substantial progress in this area by shifting from plastic to micro crystalline, high density carbon capsules, improving engineering features used to support the capsules and enhancing the structures used to fill the capsule with fusion fuel. This allowed experts to significantly increase the energy coupling efficiency from the energy produced by the laser to the energy absorbed by the capsule, and ultimately produce more energy. “Major scientific challenges still lie ahead, but recent advancements at NIF and other facilities prove that we are getting closer to achieving the ignition threshold via laser fusion,” said Spears. In 2020, the IAEA launched a new coordinated research project (CRP),
