![]() ![]() Though stellarator performances are lower than what a tokamak can achieve, its intrinsic stability and promising recent results make it a serious alternative. Finally, Europe plans to open another tokamak demonstrator, DEMO, in the 2050s.Īnother configuration called the stellarator, like Germany’s Wendelstein-7X, is showing very good results. China is also pursuing an ambitious programme to produce tritium isotopes and electricity in the 2040s. The UK has recently launched the STEP project ( Spherical Tokamak for Electricity Production), which aims to develop a reactor that connects to the energy grid in the 2040s. The first plasma is now officially expected by the end of 2025, with a demonstration of fusion expected in the late 2030s. It will be the world’s largest fusion reactor, and aims to demonstrate a gain of 10 – the plasma will be heated by 50 megawatts of power and should generate 500 megawatts. ITER, a demonstration reactor under construction in the south of France involving 35 countries, uses the tokamak configuration. The vast majority of research focuses on tokamaks, fusion reactors invented in the USSR in the 1960s, where the plasma is confined by a strong magnetic field. The magnetic confinement approach promises better development prospects and is thus the preferred route for energy production so far. Still, a reactor will have to achieve much higher gains (more than 100) to be economically attractive. The overall gain of 0.7 equals the record achieved by JET in 1997 using magnetic confinement, but in this case, the fuel absorbed 0.25 megajoules of energy and generated 1.3 megajoules: fusion therefore generated a good part of the heat needed for the reaction, approaching the point of ignition. It was this process that, on 8 August 2021, achieved the landmark energy production of 1.3 megajoules, the highest value ever recorded by the inertial approach: that is, the closest we have come to ignition. Fuel is placed inside a metal capsule a few millimetres across, which, when heated by lasers, emits X-rays that heat up and compress the fuel. The NIF uses 192 laser beams that produce a total of 1.9 megajoules of energy for a period lasting a few nanoseconds to trigger the fusion reaction. Both facilities simulate nuclear explosions for research purposes, though the NIF also carries out research on energy. ![]() The two largest inertial projects are the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in the USA and the Laser MégaJoule in France, whose applications are mainly military and funded by defence programmes. ![]() Inertial fusion also requires much higher gains to compensate for the energy consumed by the lasers. ![]() Historically, magnetic fusion has been favoured because the technology needed for inertial fusion, particularly the lasers, was not available. There are two possible ways of achieving nuclear fusion: magnetic confinement, which uses powerful magnets to confine the plasma for very long periods of time, and inertial confinement, which uses very powerful and brief laser pulses to compress the fuel and start the fusion reaction. The water evaporates into steam which turns a turbine, which in turn drives a generator to produce electricity.Inside the fusion chamber of the DIII-D tokamak, San Diego, USA. The kinetic energy of the neutrons is harnessed by the nuclear reactor and used to heat water. The reactor is covered with a thick concrete shield to ensure that no radiation is able to penetrate through and escape the reactor. To stop this happening, the reactor contains control rods, usually made of boron, which absorb some of the extra neutrons so that only a single neutrons is released per fission event. It is important that the chain reaction doesn’t get out of hand, otherwise the reactor could explode. These neutrons hit other nuclei in a chain reaction. When a neutron is absorbed by a nucleus, it undergoes a fission event, breaking apart into two nuclei and two or three neutrons. Fission only works if the neutron is moving slowly enough to be absorbed by a nucleus so nuclear reactors contain something called a moderator, usually made of graphite, which reduces the speed of the neutrons, making them more likely to be absorbed by a nucleus. Fission is used in nuclear reactors to produce energy. ![]()
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