Magnetic confinement fusion (MCF) is a method of generating nuclear fusion using magnetic fields to confine a plasma. Alongside inertial confinement fusion (ICF), MCF is one of two main research areas aiming to build controlled, functional fusion reactors for future energy generation. A number of companies and research projects are attempting to progress toward net positive fusion using magnetic confinement. This includes the ITER tokamak, the world's largest magnetic fusion device under construction in the South of France, which is due for completion. ITER aims to prove the feasibility of fusion as a large-scale, carbon-free energy source.
While there are multiple possible fusion reactions for generating energy, the most commonly used is the deuterium-tritium (D-T) reaction. This reaction involves two isotopes of hydrogen, deuterium with a nucleus consisting of one proton and one neutron, and tritium with a nucleus consisting of one proton and two neutrons. At high enough temperatures and pressures, the deuterium and tritium nuclei can collide, producing a Helium nucleus (two protons and two neutrons) and an additional neutron. Each D-T fusion reaction releases 17.6 MeV (2.8 x 10-12 J) of energy. MCF is one of the leading approaches to producing high enough energies and pressures to generate significant fusion reactions.
In MCF, hydrogen gas is heated using a range of methods (microwaves, electricity, and neutral particle beams) until it becomes a plasma. This plasma is then squeezed by super-conducting magnets, allowing fusion to occur. The electrons and ions in the (D-T) plasma follow magnetic field lines, enabling this method to isolate the fusion fuel from the reactor walls, where they would dissipate heat, slowing down or destroying the fusion reaction. The most effective magnetic configuration to confine and thermally insulate the fusion fuel is a toroidal shape (donut), where the magnetic field is curved around to form a closed loop. For proper confinement, a perpendicular field component is superimposed on the toroidal field. The resulting magnetic field produces circular and helical orbits with particles tied to field lines while still being able to move freely in the longitudinal direction of the lines.
The first magnetic confinement devices were developed in the late 1940s in the United Kingdom. These were toroidal pinches that tried to confine plasma with a purely poloidal magnetic field to produce a toroidal plasma current. They used the principle that a sufficiently strong current would create a magnetic field compressing the plasma and pulling it away from the walls of the device. However, this approach proved to be unstable.
In 1950, Soviet scientists Andrei Sakharov and Igor Tamm proposed a new type of magnetic confinement fusion device called the tokamak. This was followed by the concept of the stellarator proposed in 1951 by Lyman Spitzer. The stellarator came to dominate fusion research during the 1950s before experimental evidence showed the tokamak was a more efficient concept.
In 1973, a number of European countries came together to begin working on the Joint European Torus (JET). The European Commission approved the project in 1977, with Culham in Oxfordshire, UK chosen as the site for JET. Completed on time and on budget in 1983, JET became the largest operational magnetic confinement plasma physics experiment and the site where the first plasmas were achieved. JET also performed the first experiments using tritium, making it the first reactor to run on a 50/50 mix of tritium and deuterium. In 1997, using this fuel, JET set the record for fusion output at 16 MW from an input of 24 MW of heating. However, this was only achieved for a very short period of time, roughly 1 second.
ITER, an even larger magnetic confinement fusion experiment, was first proposed at the Geneva Superpower Summit in November 1985. The project, proposed by General Secretary Gorbachev of the former Soviet Union to US President Reagan, was intended to be an international project to develop fusion energy for peaceful purposes. In 2005, ITER members agreed the experiment would be built in Cadarache, France. In December 2022, the ITER project passed the 77.7% milestone of work scope completed to the first plasma.
