Magnetic confinement fusion

Magnetic confinement fusion is an approach to generate thermonuclear fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach dates into the 1940s and has seen the majority of development since then. It is usually considered more promising for practical power production. Magnetic confinement fusion is an approach to generate thermonuclear fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach dates into the 1940s and has seen the majority of development since then. It is usually considered more promising for practical power production. Fusion reactions combine light atomic nuclei such as hydrogen to form heavier ones such as helium, producing energy. In order to overcome the electrostatic repulsion between the nuclei, they must have a temperature of several tens of millions of degrees, under which conditions they no longer form neutral atoms but exist in the plasma state. In addition, sufficient density and energy confinement are required, as specified by the Lawson criterion. At these temperatures, no material container could withstand the extreme heat of the plasma. Magnetic confinement fusion attempts to create these conditions by using the electrical conductivity of the plasma to contain it with magnetic fields. The basic concept can be thought of in a fluid picture as a balance between magnetic pressure and plasma pressure, or in terms of individual particles spiralling along magnetic field lines. Developing a suitable arrangement of fields that contain the fuel ions without introducing turbulence or leaking the fuel at a profuse rate has proven to be a difficult problem. The development of magnetic fusion energy (MFE) has gone through three distinct phases. In the 1950s it was believed MFE would be relatively easy to achieve, and this developed into a race to build a suitable machine. By the late 1950s, it was clear that turbulence and instabilities in the plasma were a serious problem, and during the 1960s, 'the doldrums', effort turned to a better understanding of the physics of plasmas. In 1968, a Soviet team invented the tokamak magnetic confinement device, which demonstrated performance ten times better than the best alternatives. Since then the MFE field has been dominated by the tokamak approach. Construction of a 500-MW power generating fusion plant using this design, the ITER, began in France in 2007 and is scheduled to begin operation 2025. A major area of research in the early years of fusion energy research was the magnetic mirror. Most early mirror devices attempted to confine plasma near the focus of a non-planar magnetic field generated in a solenoid with the field strength increased at either end of the tube. In order to escape the confinement area, nuclei had to enter a small annular area near each magnet. It was known that nuclei would escape through this area, but by adding and heating fuel continually it was felt this could be overcome. In 1954, Edward Teller gave a talk in which he outlined a theoretical problem that suggested the plasma would also quickly escape sideways through the confinement fields. This would occur in any machine with convex magnetic fields, which existed in the centre of the mirror area. Existing machines were having other problems and it was not obvious whether this was occurring. In 1961, a Soviet team conclusively demonstrated this flute instability was indeed occurring, and when a US team stated they were not seeing this issue, the Soviets examined their experiment and noted this was due to a simple instrumentation error.