Fusion power
Fusion power is the technique of extracting net energy from a nuclear fusion reaction. Technically, most forms of power generation are indirectly fusion-powered, since the Sun is an extremely large natural fusion reactor and its radiation drives most energetic phenomena here on Earth, but the term is usually only used to refer to artifically sustained nuclear fusion.
Humanity has been able to create artifical large-scale fusion reactions since 1949, when the United States test-detonated a hydrogen bomb. However, an uncontrolled explosive reaction of that magnitude is not well-suited to power generation. Theoretically, one could use existing large fusion bombs as a source of power by detonating them deep underground and then using the resulting heated cavern as a source of geothermal energy, but such a power plant is unlikely to ever be constructed for a variety of reasons.
Controlled nuclear fusion within a containment vessel has been possible for some time, but it remains quite difficult to achieve break-even. There are three types of break-even points: being able to generate as much energy from the reaction as you put in, being able to extract as much energy from the reaction as you put in, and being able to extract as much money from the system as you put in.
Confinement in fusion reactions is achieved by any of several techniques: magnetically, as in the Tokamak reactor, electrostatically, using a sort of vacuum tube called a fusor, or inertially, by evaporating the surface of a small pellet of fuel. Most controversially, some researchers have claimed to observe neutron production in electrochemical systems, the so-called cold fusion systems.
The different forms of reactor all have advantages and disadvantages. Tokamaks are the most developed, and after development, exceeded fursors in neutron production per volume of plasma. Fusors have tolerant design parameters, and can use a wider range of fuels, permitting low-radiation operation. They might also permit direct conversion of nuclear energy to electricity. Inertial confinement produces plasmas with impressive densities and temperatures, and might be best suited to research, X-ray generation, very small reactors, and rocketry.
It's clear that researchers and funding agencies have tried to pick winners, rather than pursuing all practicable options. Fusor research funding has been at a near standstill for many years. The proposed ITER would use magnetic confinement, and some persons believe that this would effectively kill off research into the inertial design regardless of its merits.
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