Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors.
Fusion processes require fuel and a confined environment with sufficient temperature, pressure, and confinement time to create a plasma in which fusion can occur. The combination of these figures that results in a power-producing system is known as the Lawson criterion. In stars, the most common fuel is hydrogen, and gravity provides extremely long confinement times that reach the conditions needed for fusion energy production. Proposed fusion reactors generally use hydrogen isotopes such as deuterium and tritium (and especially a mixture of the two), which react more easily than hydrogen to allow them to reach the Lawson criterion requirements with less extreme conditions. Most designs aim to heat their fuel to around 100 million degrees, which presents a major challenge in producing a successful design.
As a source of power, nuclear fusion is expected to have many advantages over fission. These include reduced radioactivity in operation and little high-level nuclear waste, ample fuel supplies, and increased safety. However, the necessary combination of temperature, pressure, and duration has proven to be difficult to produce in a practical and economical manner. Research into fusion reactors began in the 1940s, but to date, no design has produced more fusion power output than the electrical power input.[1] A second issue that affects common reactions is managing neutrons that are released during the reaction, which over time degrade many common materials used within the reaction chamber.
Fusion researchers have investigated various confinement concepts. The early emphasis was on three main systems: z-pinch, stellarator, and magnetic mirror. The current leading designs are the tokamak and inertial confinement (ICF) by laser. Both designs are under research at very large scales, most notably the ITER tokamak in France, and the National Ignition Facility (NIF) laser in the United States. Researchers are also studying other designs that may offer cheaper approaches. Among these alternatives, there is increasing interest in magnetized target fusion and inertial electrostatic confinement, and new variations of the stellarator.
https://en.wikipedia.org/wiki/Fusion_power
A magnetic mirror, known as a magnetic trap (магнитный захват) in Russia and briefly as a pyrotron in the US, is a type of magnetic confinement device used in fusion power to trap high temperature plasma using magnetic fields. The mirror was one of the earliest major approaches to fusion power, along with the stellarator and z-pinchmachines.
In a classic magnetic mirror, a configuration of electromagnets is used to create an area with an increasing density of magnetic field lines at either end of the confinement area. Particles approaching the ends experience an increasing force that eventually causes them to reverse direction and return to the confinement area.[1] This mirror effect will only occur for particles within a limited range of velocities and angles of approach, those outside the limits will escape, making mirrors inherently "leaky".
An analysis of early fusion devices by Edward Teller pointed out that the basic mirror concept is inherently unstable. In 1960, Soviet researchers introduced a new "minimum-B" configuration to address this, which was then modified by UK researchers into the "baseball coil" and by the US to "yin-yang magnet" layout. Each of these introductions led to further increases in performance, damping out various instabilities, but requiring ever-larger magnet systems. The tandem mirror concept, developed in the US and Russia at about the same time, offered a way to make energy-positive machines without requiring enormous magnets and power input.
By the late 1970s, many of the design problems were considered solved, and Lawrence Livermore Laboratory began the design of the Mirror Fusion Test Facility (MFTF) based on these concepts. The machine was completed in 1986, but by this time, experiments on the smaller Tandem Mirror Experimentrevealed new problems. In a round of budget cuts, MFTF was mothballed, and eventually scrapped. A fusion reactor concept called the Bumpy torus made use of a series of magnetic mirrors joined in a ring. It was investigated at the Oak Ridge National Laboratory until 1986.[2] The mirror approach has since seen less development, in favor of the tokamak, but mirror research continues today in countries like Japan and Russia.[3]
https://en.wikipedia.org/wiki/Magnetic_mirror
Magnetic confinement fusion is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, along with inertial confinement fusion. The magnetic approach began in the 1940s and absorbed the majority of subsequent development.
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 tens of millions of degrees, creating a plasma. In addition, the plasma must be contained at a sufficient density for a sufficient time, as specified by the Lawson criterion (triple product).
Magnetic confinement fusion attempts to use the electrical conductivity of the plasma to contain it through interaction with magnetic fields. The magnetic pressure offsets the plasma pressure. Developing a suitable arrangement of fields that contain the fuel without excessive turbulence or leaking is the primary challenge of this technology.
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https://en.wikipedia.org/wiki/Magnetic_confinement_fusion
Magnetic pressure is an energy density associated with a magnetic field. Any magnetic field has an associated magnetic pressure contained by the boundary conditions on the field. It is identical to any other physical pressure except that it is carried by the magnetic field rather than (in the case of a gas) by the kinetic energy of gas molecules. A gradient in field strength causes a force due to the magnetic pressure gradient called the magnetic pressure force.
The magnetic pressure force is readily observed in an unsupported loop of wire. If an electric current passes through the loop, the wire serves as an electromagnet, such that the magnetic field strength inside the loop is much greater than the field strength just outside the loop. This gradient in field strength gives rise to a magnetic pressure force that tends to stretch the wire uniformly outward. If enough current travels through the wire, the loop of wire will form a circle. At even higher currents, the magnetic pressure can create tensile stress that exceeds the tensile strength of the wire, causing it to fracture, or even explosively fragment. Thus, management of magnetic pressure is a significant challenge in the design of ultrastrong electromagnets.
The force (in cgs) F exerted on a coil by its own current is[1]
![{\displaystyle \mathbf {F} ={\dfrac {I^{2}}{c^{2}R}}\left[\ln \left({\dfrac {8R}{a}}\right)-1+Y\right]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e457554825aa1a2189ee2576e774eec766448939)
where Y is the internal inductance of the coil, defined by the distribution of current. Y is 0 for high frequency currents carried mostly by the outer surface of the conductor, and 0.25 for DC currents distributed evenly throughout the conductor. See inductance for more information.
Interplay between magnetic pressure and ordinary gas pressure is important to magnetohydrodynamics and plasma physics. Magnetic pressure can also be used to propel projectiles; this is the operating principle of a railgun.
If any currents present are parallel to a magnetic field, the field lines follow shapes in which the magnetic pressure gradient is balanced by the magnetic tension force. Such a field configuration is called force-free because there is no Lorentz force (). The familiar potential magnetic field is a special case of a force-free field: potential field configurations occupy space that contains no electric current at all.
The magnetic pressure is given in SI units (P in Pa, B in T, μ0 in H/m) by
and in cgs units (P in dyn/cm², B in G) by
- .
In practical units,
![{\displaystyle P_{B}{\text{ [bar]}}\approx \left({\frac {B{\text{ [T]}}}{0.501}}\right)^{2}.}](https://wikimedia.org/api/rest_v1/media/math/render/svg/9015e3823c3b5ae512ea3137d5c064e0e5d23e55)
See also[edit]
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