Levitated dipole

A levitated dipole is a type of nuclear fusion reactor design using a superconducting torus which is magnetically levitated inside the reactor chamber. The name refers to the magnetic dipole that forms within the reaction chamber, similar to Earth's or Jupiter's magnetospheres. It is believed that such an apparatus could contain plasma more efficiently than other fusion reactor designs. The concept of the levitated dipole as a fusion reactor was first theorized by Akira Hasegawa in 1987. The Earth's magnetic field is generated by the circulation of charges in the Earth's molten core. The resulting magnetic dipole field forms a shape with magnetic field lines passing through the Earth's center, reaching the surface near the poles and extending far into space above the equator. Charged particles entering the field will tend to follow the lines of force, moving north or south. As they reach the polar regions, the magnetic lines begin to cluster together, and this increasing field can cause particles below a certain energy threshold to reflect, and begin travelling in the opposite direction. Such particles bounce back and forth between the poles until they collide with other particles. Particles with greater energy continue towards the Earth, impacting the atmosphere and causing the aurora. This basic concept is used in the magnetic mirror approach to fusion energy. The mirror uses a solenoid to confine the plasma in the center of a cylinder, and then two magnets at either end to force the magnetic lines closer together to create reflecting areas. One of the most promising of the early approaches to fusion, the mirror ultimately proved to be very "leaky", with the fuel refusing to properly reflect from the ends as the density and energy were increased. Annoyingly, it was the particles with the most energy, those most likely to undergo fusion, that preferentially escaped. Research into large mirror machines ended in the 1980s as it became clear they would not reach fusion breakeven in a practically sized device.