The Sun is a natural fusion reactor.

Fusion power is useful energy generated by nuclear fusion reactions. In this kind of reaction two light atomic nuclei fuse together to form a heavier nucleus and release energy. The largest current experiment, JET, has resulted in fusion power production somewhat larger than the power put into the plasma, maintained for a few seconds. In June 2005, the construction of the experimental reactor ITER, designed to produce several times more fusion power than the power into the plasma over many minutes, was announced. The production of net electrical power from fusion is planned for the next generation experiment after ITER. Download high resolution version (640x620, 61 KB) This image is not licensed under the GFDL. It is under a non-commercial-use only licence. ... Download high resolution version (640x620, 61 KB) This image is not licensed under the GFDL. It is under a non-commercial-use only licence. ... The Sun is the spectral type G2V yellow star at the center of Earths solar system. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... A stylized Bohr model-like representation of a lithium atom. ... Split image of JET with right side showing hot plasma during a shot. ... Cutaway of the ITER Tokamak Torus in casing. ...

Fuel cycle

For two nuclei to fuse, they must collide with enough energy to overcome the repulsive electrostatic force between them. Most fusion generation experiments therefore raise their fuel to very high temperatures. If two light nuclei come close enough to each other, they may fuse to form a single nucleus with a slightly smaller mass than the sum of their original masses. The difference in mass is released as energy according to Einstein's relationship E = mc². (If the input nuclei are sufficiently massive, the resulting fusion product will be heavier than the reactants, and the reaction requires the addition of energy to convert into the additional mass; in this case the reverse process of nuclear fission will release energy, which can be used, for example, in nuclear reactors or bombs.) In physics, the electrostatic force is the force arising between static (that is, non-moving) electric charges. ... A display of the famous equation on Taipei 101 during the event of the World Year of Physics 2005. ... An induced nuclear fission event. ...

Hydrogen, the most abundant element in the universe, also has the smallest nuclear charge and therefore reacts at the lowest temperature. Helium has an extremely low mass per nucleon and therefore is energetically favored as a fusion product. As a consequence, most fusion reactions combine isotopes of hydrogen ("protium", deuterium, or tritium) to form isotopes of helium (³He or ⁴He). General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... A hydrogen atom is an atom of the element hydrogen. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ... Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ...

Unsolved problems in physics: Is it possible to construct a practical nuclear reactor that is powered by nuclear fusion rather than nuclear fission?

Perhaps the three most widely considered fuel cycles are based on the D-T, D-D, and p-¹¹B reactions. Other fuel cycles (D-³He and ³He-³He) would require a supply of ³He, either from other nuclear reactions or from extra-terrestrial sources, such as the surface of the moon or the atmospheres of the gas giant planets. The details of the calculations comparing these reactions can be found here. Image File history File links Question_dropshade. ... This is an incomplete list of some of the unsolved problems in physics. ... Core of a nuclear reactor A nuclear power station. ... An induced nuclear fission event. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ...

The D-T fuel cycle

Diagram of the D-T reaction

The easiest and most immediately promising nuclear reaction to be used for fusion power is: kuhy File links The following pages link to this file: Nuclear fusion ... kuhy File links The following pages link to this file: Nuclear fusion ... In nuclear fusion research, the Lawson criterion, first derived by John D. Lawson in 1957, is an important general measure of a system that defines the conditions needed for a fusion reactor to reach ignition, that is, that the heating of the plasma by the products of the fusion reactions...

D + T → ⁴He + n

Deuterium is a naturally occurring isotope of hydrogen and as such is universally available. The large mass ratio of the hydrogen isotopes makes the separation rather easy compared to the difficult uranium enrichment process. Tritium is also an isotope of hydrogen, but it occurs naturally in only negligible amounts due to its radioactive half-life of 12 years. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions: Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ... Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ... Helium-4 is a non-radioactive and light isotope of helium. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Isotopes are forms of an element whose nuclei have the same atomic number - the number of protons in the nucleus - but different mass numbers because they contain different numbers of neutrons. ... Enriched uranium is uranium whose uranium-235 content has been increased through the process of isotope separation. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... A breeder reactor is a nuclear reactor that breeds fuel by producing more fissile material than it consumes. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ...

n + ⁶Li → T + ⁴He

n + ⁷Li → T + ⁴He + n

The reactant neutron is supplied by the D-T fusion reaction shown above, the one which also produces the useful energy. The reaction with ⁶Li is exothermic, providing a small energy gain for the reactor. The reaction with ⁷Li is endothermic but does not consume the neutron. At least some ⁷Li reactions are required to replace the neutrons lost by reactions with other elements. Most reactor designs use the naturally occurring mix of lithium isotopes. The supply of lithium is more limited than that of deuterium, but still large enough to supply the world's energy for hundreds of years. In chemistry, an exothermic reaction is one that releases heat. ... In chemistry, an endothermic reaction is one in which the products have more energy than the reactants, and thus a net input of energy, usually in the form of heat, is required. ...

Several drawbacks are commonly attributed to D-T fusion power.

1. It produces substantial amounts of neutrons that result in induced radioactivity within the reactor structure, and it requires the handling of the radioisotope tritium.
2. Only about 20% of the fusion energy yield appears in the form of charged particles (the rest neutrons), which limits the extent to which direct energy conversion techniques might be applied.
3. The use of D-T fusion power depends on lithium resources, which are less abundant than deuterium resources.

The neutron flux expected in a commercial D-T fusion reactor is about 100 times that of current fission power reactors, posing problems for material design. Design of suitable materials is underway but their actual use in a reactor is not proposed until the generation after ITER. After a single series of D-T tests at JET, the largest fusion reactor yet to use this fuel, the vacuum vessel was sufficiently radioactive that remote handling needed to be used for the year following the tests. neutron flux n : the rate of flow of neutrons; the number of neutrons passing through a unit area in unit time via dictionary. ... Cutaway of the ITER Tokamak Torus in casing. ... Split image of JET with right side showing hot plasma during a shot. ...

On the other hand, the volumetric deposition of neutron power can also be seen as an advantage. If all the power of a fusion reactor had to be transported by conduction through the surface enclosing the plasma, it would be very difficult to find materials and a construction that would survive, and it would probably entail a relatively poor efficiency.

The D-D fuel cycle

After the reaction of tritium with deuterium, it is easiest to achieve fusion through the reaction of deuterium with itself. This reaction has two branches that occur with nearly equal probability:

D + D	→ T	+ p
	→ 3He	+ n

The optimum temperature for this reaction is 15 keV, only slightly higher than the optimum for the D-T reaction. The first branch does not produce neutrons, but it does produce tritium, so that a D-D reactor will not be completely tritium-free, even though it does not require an input of tritium or lithium. Most of the tritium produced will be burned before leaving the reactor, which reduces the tritium handling required, but also means that more neutrons are produced and that some of these are very energetic. The neutron from the second branch has an energy of only 2.45 MeV, whereas the neutron from the D-T reaction has an energy of 14.1 MeV, resulting in a wider range of isotope production and material damage. Assuming complete tritium burn-up, the reduction in the fraction of fusion energy carried by neutrons is only about 18%, so that the primary advantage of the D-D fuel cycle is that tritium breeding is not required. Other advantages are independence from limitations of lithium resources and a somewhat softer neutron spectrum. The price to pay compared to D-T is that the energy confinement (at a given pressure) must be 30 times better and the power produced (at a given pressure and volume) is 68 times less.

The p-¹¹B fuel cycle

If aneutronic fusion is the goal, then the ideal reaction may be the proton-boron reaction: Aneutronic fusion is a (hypothetical) form of fusion power where no more than 1% of the total fusion energy released is carried by neutrons. ...

p + ¹¹B → 3 ⁴He

Under reasonable assumptions, side reactions will result in about 0.1% of the fusion power being carried by neutrons. With 123 keV, the optimum temperature for this reaction is nearly ten times higher than that for the pure hydrogen reactions, the energy confinement must be 500 times better than that required for the D-T reaction, and the power density will be 2500 times lower than for D-T.

Safety and environmental issues

Accident potential

The likelihood of a catastrophic accident in a fusion reactor in which injury or loss of life occurs is much smaller than that of a fission reactor. The primary reason is that the fuel contained in the reaction chamber is only enough to sustain the reaction for about a minute, whereas a fission reactor contains about a year's supply of fuel. Furthermore, fusion requires very extreme and precisely controlled conditions of temperature, pressure and magnetic field parameters. If the reactor were damaged, these would be disrupted and the reaction would be rapidly quenched. Core of a nuclear reactor A nuclear power station. ...

Effluents during normal operation

The natural product of the fusion reaction is a small amount of helium, which is completely harmless to life and does not contribute to global warming. Of more concern is tritium, which, like other isotopes of hydrogen, is difficult to retain completely. During normal operation, some amount of tritium will be continually released. There would be no acute danger, but the cumulative effect on the world's population from a fusion economy could be a matter of concern. The 12 year half-life of tritium would at least prevent unlimited build-up and long-term contamination. Global mean surface temperatures 1856 to 2005 Mean temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980 Global warming is a term used to describe the trend of increases in the average temperature of the Earths atmosphere and oceans that... Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ...

Waste management

The large flux of high-energy neutrons in a reactor will make the structural materials radioactive. The radioactive inventory at shut-down may be comparable to that of a fission reactor, but there are important differences. The half-life of the radioisotopes produced by fusion tend to be less than those from fission, so that the inventory decreases more rapidly. Furthermore, there are fewer unique species, and they tend to be non-volatile and biologically less active. As opposed to nuclear fission, where there is hardly any possibility to influence the spectrum of fission products, the problems can be further reduced by careful choice of the materials used. "Low activation" materials like vanadium, for example, would become much less radioactive than stainless steel. Such materials would have half-lives of tens of years, rather than the thousands of years for radioactive waste produced from fission. This involves the design of new alloys with unusual chemical compositions -- a complex process as the chemical composition also affects the materials' mechanical properties. A radionuclide is an atom with an unstable nucleus. ... Vanadium is a chemical element in the periodic table that has the symbol V and atomic number 23. ... In metallurgy, stainless steel (inox) is defined as a ferrous alloy with a minimum of 10. ... Half-Life is a science fiction first-person shooter computer game developed by Valve Software and published by Sierra Studios in 1998, based on a heavily-modified Quake game engine. ...

Nuclear proliferation

Although fusion power uses nuclear technology, the overlap with nuclear weapons technology is small. Tritium is a component of the trigger of hydrogen bombs, but not a major problem in production. The copious neutrons from a fusion reactor could be used to breed plutonium for an atomic bomb, but not without extensive redesign of the reactor, so that clandestine production would be easy to detect. The theoretical and computational tools needed for hydrogen bomb design are closely related to those needed for inertial confinement fusion, but have very little in common with (the more scientifically developed) magnetic confinement fusion. Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, in 1945 lifted nuclear fallout some 18 km (60,000 feet) above the epicenter. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (244) g/mol Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... Inertial confinement fusion using lasers rapidly progressed in the late 1970s and early 1980s from being able to deliver only a few joules of laser energy to a fusion target to being able to deliver tens of kilojoules to a target. ... The magnetic fusion energy (MFE) program seeks to establish the conditions to sustain a nuclear fusion reaction in a plasma that is contained by magnetic fields. ...

Fusion power as a sustainable energy source

Fusion power is often described as a "clean", "renewable", or "sustainable" energy source. While, like most forms of renewable energy, it has the potential to be used indefinitely, large scale reactors using neutronic fuels (e.g. ITER) and thermal power production (turbine based) are in fact most comparable from an engineering and economics viewpoint to fission power. Both fission and fusion power plants involve a relatively compact heat source powering a conventional steam turbine based power plant, while producing enough neutron radiation to make activation of the plant materials problematic. The main distinction is that fusion power produces no high-level radioactive waste (though activated plant materials still need to be disposed of). There are some power plant ideas which may significantly lower the cost or size of such plants, however research in these areas is nowhere near as advanced as in tokamaks. Renewable energy (sources) or RES capture their energy from existing flows of energy, from on-going natural processes, such as sunshine, wind, flowing water, biological processes, and geothermal heat flows. ... Sustainable energy sources are energy sources which are sustainable, that is not expected to be depleted in a human timeframe, and which contribute to the sustainability of all species. ... Renewable energy (sources) or RES capture their energy from existing flows of energy, from on-going natural processes, such as sunshine, wind, flowing water, biological processes, and geothermal heat flows. ... A nuclear power station. ... Neutron activation is the process by which neutron radiation induces radioactivity in materials. ... A split image of the largest tokamak in the world, the JET, showing hot plasma in the right image during a shot. ...

Theoretical Power plant designs

Confinement concepts

Parameter space occupied by inertial fusion energy and magnetic fusion energy devices. The regime allowing thermonuclear ignition with high gain lies near the upper right corner of the plot.

Confinement refers to all the conditions necessary to keep a plasma dense and hot long enough to undergo fusion: Image File history File links Download high resolution version (936x793, 98 KB)Plot showing parameter space occupied by both MFE and IFE methods of attaining fusion showing specifically, the shiva, NOVA and NIF lasers at LLNL. Taken from [1] File history Legend: (cur) = this is the current file, (del) = delete... Image File history File links Download high resolution version (936x793, 98 KB)Plot showing parameter space occupied by both MFE and IFE methods of attaining fusion showing specifically, the shiva, NOVA and NIF lasers at LLNL. Taken from [1] File history Legend: (cur) = this is the current file, (del) = delete... In inertial confinement fusion (ICF), nuclear fusion reactions are initiated by heating and compressing a target – a pellet that most often contains deuterium and tritium – by the use of intense laser or ion beams. ... The magnetic fusion energy (MFE) program seeks to establish the conditions to sustain a nuclear fusion reaction in a plasma that is contained by magnetic fields. ...

• Equilibrium: There must be no net forces on any part of the plasma, otherwise it will rapidly disassemble. The exception, of course, is inertial confinement, where the relevant physics must occur faster than the disassembly time.
• Stability: The plasma must be so constructed that small deviations are restored to the initial state, otherwise some unavoidable disturbance will occur and grow exponentially until the plasma is destroyed.
• Transport: The loss of particles and heat in all channels must be sufficiently slow. The word "confinement" is often used in the restricted sense of "energy confinement".

The first human-made, large-scale production of fusion reactions was the test of the hydrogen bomb, Ivy Mike, in 1952. It was once proposed to use hydrogen bombs as a source of power by detonating them in underground caverns and then generating electricity from the heat produced, but such a power plant is unlikely ever to be constructed, for a variety of reasons. (See the PACER project for more details.) Controlled thermonuclear fusion (CTF) refers to the alternative of continuous power production, or at least the use of explosions that are so small that they do not destroy a significant portion of the machine that produces them. A standard definition of mechanical equilibrium is: A system is in mechanical equilibrium when the sum of the forces, and torques, on each particle of the system is zero. ... An important field of plasma physics is the stability of the plasma. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, in 1945 lifted nuclear fallout some 18 km (60,000 feet) above the epicenter. ... The mushroom cloud from the Mike shot. ... 1952 (MCMLII) was a Leap year starting on Tuesday (link will take you to calendar). ... Pacer could refer to: A type of British train, see Pacer (train). ...

To produce self-sustaining fusion, the energy released by the reaction (or at least a fraction of it) must be used to heat new reactant nuclei and keep them hot long enough that they also undergo fusion reactions. Retaining the heat is called energy confinement and may be accomplished in a number of ways.

The hydrogen bomb really has no confinement at all. The fuel is simply allowed to fly apart, but it takes a certain length of time to do this, and during this time fusion can occur. This approach is called inertial confinement. If more than about a milligram of fuel is used, the explosion would destroy the machine, so controlled thermonuclear fusion using inertial confinement causes tiny pellets of fuel to explode several times a second. To induce the explosion, the pellet must be compressed to about 30 times solid density with energetic beams. If the beams are focused directly on the pellet, it is called direct drive, which can in principle be very efficient, but in practice it is difficult to obtain the needed uniformity. An alternative approach is indirect drive, in which the beams heat a shell, and the shell radiates x-rays, which then implode the pellet. The beams are commonly laser beams, but heavy and light ion beams and electron beams have all been investigated. Inertial confinement fusion using lasers rapidly progressed in the late 1970s and early 1980s from being able to deliver only a few joules of laser energy to a fusion target to being able to deliver tens of kilojoules to a target. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... An ion beam is a stream of charged particles, which has many uses in electronics manufacturing (principally ion implantation) and other industries. ...

Inertial confinement produces plasmas with impressive densities and temperatures, and appear to be best suited to weapons research, X-ray generation, very small reactors, and perhaps in the distant future, spaceflight. They rely on fuel pellets with a "perfect" shape in order to generate a symmetrical inward shock wave to produce the high-density plasma, and in practice these have proven difficult to produce. A recent development in the field of laser induced ICF is the use of ultrashort pulse multi-petawatt lasers to heat the plasma of an imploding pellet at exactly the moment of greatest density after it is imploded conventionally using terawatt scale lasers. This research will be carried out on the (currently being built) OMEGA EP petawatt and OMEGA lasers at the University of Rochester and at the GEKKO XII laser at the institute for laser engineering in Osaka Japan, which if fruitful, may have the effect of greatly reducing the cost of a laser fusion based power source. In fluid dynamics, a shock wave is a nonlinear or discontinuous pressure wave. ... This page lists examples of the power in watts produced by various different sources of energy. ... For other uses of the acronym LLE see: LLE (disambiguation) The Laboratory for Laser Energetics (LLE) is a scientific research facility which is part of the University of Rochesters south campus, located in Rochester, New York. ... Located in Rochester, New York, USA and founded in 1850, the University of Rochester is a private, coeducational and nonsectarian research institution. ...

At the temperatures required for fusion, the fuel is in the form of a plasma with very good electrical conductivity. This opens the possibility to confine the fuel and the energy with magnetic fields, an idea known as magnetic confinement. The Lorenz force works only perpendicular to the magnetic field, so that the first problem is how to prevent the plasma from leaking out the ends of the field lines. There are basically two solutions. Electrical conductivity is a measure of a materials ability to conduct an electric current. ... It has been suggested that Magnetic field density be merged into this article or section. ... The magnetic fusion energy (MFE) program seeks to establish the conditions to sustain a nuclear fusion reaction in a plasma that is contained by magnetic fields. ... In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ...

The first is to use the magnetic mirror effect. If particles following a field line encounter a region of higher field strength, then some of the particles will be stopped and reflected. Advantages of a magnetic mirror power plant would be simplified construction and maintenance due to a linear topology and the potential to apply direct conversion in a natural way, but the confinement achieved in the experiments was so poor that this approach has been essentially abandoned. A magnetic mirror is a magnetic field configuration where the field strength changes when moving along a field line. ...

The second possibility to prevent end losses is to bend the field lines back on themselves, either in circles or more commonly in nested toroidal surfaces. The most highly developed system of this type is the tokamak, with the stellarator being a distant second, but still a serious contender. A third toroidal machine type is the Reversed-Field Pinch, which was never sufficiently able to realize its potential advantages. Compact toroids, especially the Field-Reversed Configuration and the spheromak, attempt to combine the advantages of toroidal magnetic surfaces with those of a simply connected (non-toroidal) machine. Compact toroids still have some enthusiastic supporters but are not backed as readily by the majority of the fusion community. A torus. ... A split image of the largest tokamak in the world, the JET, showing hot plasma in the right image during a shot. ... Stellarator magnetic field and magnets A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. ... Reversed-Field Pinch (RFP) is a toroidal magnetic confinement scheme. ... A Field-Reversed Configuration (FRC) is a device developed for magnetic fusion energy research that confines a plasma on closed magnetic field lines without a central penetration. ... This article needs to be cleaned up to conform to a higher standard of quality. ... A geometrical object is called simply connected if it consists of one piece and doesnt have any circle-shaped holes or handles. Higher-dimensional holes are allowed. ...

A split image of the largest tokamak in the world, the JET, showing hot plasma in the right image during a shot.

A more subtle technique is to use more unusual particles to catalyse fusion. The best known of these is Muon-catalyzed fusion which uses muons, which behave somewhat like electrons and replace the electrons around the atoms. These muons allow atoms to get much closer and thus reduce the kinetic energy required to initiate fusion. Muons require more energy to produce than we can get back from muon-catalysed fusion, making this approach impractical for the generation of power. Image File history File links Download high resolution version (1000x579, 150 KB)An image of the inside of the JET tokamak with image on right showing plasma during a shot. ... Image File history File links Download high resolution version (1000x579, 150 KB)An image of the inside of the JET tokamak with image on right showing plasma during a shot. ... A split image of the largest tokamak in the world, the JET, showing hot plasma in the right image during a shot. ... Split image of JET with right side showing hot plasma during a shot. ... Muon-catalyzed fusion is a process allowing nuclear fusion to take place at room temperature. ...

Finally, there are also electrostatic confinement fusion systems, in which ions in the reaction chamber are confined and held at the center of the device by electrostatic forces, as in the Farnsworth-Hirsch Fusor, but these are not believed capable of being developed into a practical power plant. Inertial electrostatic confinement (often abbreviated as IEC) of a plasma can be achieved with electrostatic fields which accelerate charged particles (either ions or electrons) directly, in a confined space. ... // An ion is an atom, group of atoms, or subatomic particle with a net electric charge. ... US3386883 - fusor -- June 4, 1968 The Farnsworth-Hirsch Fusor, or simply fusor, is an apparatus designed by Philo T. Farnsworth to create nuclear fusion. ...

Most controversially, some researchers have claimed to observed excess heat, neutrons, tritium, helium and other nuclear effects in so-called cold fusion systems. Most scientists consider cold fusion to be a pseudoscience. A peer review panel was commissioned by the US Department of Energy to study these claims [1] [2] and the majority of the panel did not consider the evidence for low energy nuclear reactions convincing, nor did any of the panel members advocate funding for cold fusion. However, some researchers, including some from Los Alamos, and the Naval Research Laboratory[3] continue to conduct research relating to cold fusion. Research into sonoluminescence induced fusion, sometimes known as "bubble fusion", also continues, although it is met with skepticism almost equal to cold fusion by most of the scientific community. Charles Bennett examines three cold fusion test cells at the Oak Ridge National Laboratory, USA Cold fusion is a nuclear fusion reaction which its proponents claim occurs well below the temperature required for thermonuclear reactions (millions of degrees Celsius) in a relatively small table top apparatus. ... Phrenology is regarded today as being a classic example of pseudoscience. ... Long exposure image of multi-bubble sonoluminescence created by a high intensity ultrasonic horn immersed in a beaker of liquid. ...

Subsystems

In fusion research, achieving a fusion energy gain factor Q = 1 is called breakeven and is considered a significant although somewhat artificial milestone. Ignition refers to an infinite Q, that is, a self-sustaining plasma where the losses are made up for by fusion power without any external input. In a practical fusion reactor, some external power will always be required for things like current drive, refueling, profile control, and burn control. A value on the order of Q = 20 will be required if the plant is to deliver much more energy than it uses internally. The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state. ...

There have been many design studies for fusion power plants. Despite many differences, there are several systems that are common to most. To begin with, a fusion power plant, like a fission power plant, is customarily divided into the nuclear island and the balance of plant. The balance of plant is the conventional part that converts high-temperature heat into electricity via steam turbines. It is much the same in a fusion power plant as in a fission or coal power plant. In a fusion power plant, the nuclear island has a plasma chamber with an associated vacuum system, surrounded by a plasma-facing components (first wall and divertor) maintaining the vacuum boundary and absorbing the thermal radiation coming from the plasma, surrounded in turn by a blanket where the neutrons are absorbed to breed tritium and heat a working fluid that transfers the power to the balance of plant. If magnetic confinement is used, a magnet system, using primarily cryogenic superconducting magnets, is needed, and usually systems for heating and refueling the plasma and for driving current. In inertial confinement, a driver (laser or accelerator) and a focusing system are needed, as well as a means for forming and positioning the pellets. A nuclear power station. ... A rotor of a modern steam turbine, used in a power plant A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work. ...

Although the standard solution for electricity production in fusion power plant designs is conventional steam turbines using the heat deposited by neutrons, there are also designs for direct conversion of the energy of the charged particles into electricity. These are of little value with a D-T fuel cycle, where 80% of the power is in the neutrons, but are indispensable with aneutronic fusion, where less than 1% is. Direct conversion has been most commonly proposed for open-ended magnetic configurations like magnetic mirrors or Field-Reversed Configurations, where charged particles are lost along the magnetic field lines, which are then expanded to convert a large fraction of the random energy of the fusion products into directed motion. The particles are then collected on electrodes at various large electrical potentials. Typically the claimed conversion efficiency is in the range of 80%, but the converter may approach the reactor itself in size and expense. Aneutronic fusion is a (hypothetical) form of fusion power where no more than 1% of the total fusion energy released is carried by neutrons. ... A magnetic mirror is a magnetic field configuration where the field strength changes when moving along a field line. ... A Field-Reversed Configuration (FRC) is a device developed for magnetic fusion energy research that confines a plasma on closed magnetic field lines without a central penetration. ...

Materials

Developing materials for fusion reactors has long been recognized as a problem nearly as difficult and important as that of plasma confinement, but it has received only a fraction of the attention. The neutron flux in a fusion reactor is expected to be about 100 times that in existing pressurized water reactors (PWR). Each atom in the blanket of a fusion reactor is expected to be hit by a neutron and displaced about a hundred times before the material is replaced. Furthermore the high-energy neutrons will produce hydrogen and helium in various nuclear reactions that tends to form bubbles at grain boundaries and result in swelling, blistering or embrittlement. One also wishes to choose materials whose primary components and impurities do not result in long-lived radioactive wastes. Finally, the mechanical forces and temperatures are large, and there may be frequent cycling of both. A pressurised water reactor (PWR) is a type of nuclear power reactor that uses ordinary light water for both coolant and for neutron moderation. ...

The problem is exacerbated because realistic material tests must expose samples to neutron fluxes of a similar level for a similar length of time as those expected in a fusion power plant. Such a neutron source is nearly as complicated and expensive as a fusion reactor itself would be. Proper materials testing will not be possible in ITER, and a proposed materials testing facility, IFMIF, is still at the design stage in 2005. Cutaway of the ITER Tokamak Torus in casing. ... The International Fusion Material Irradiation Facility is an international scientific research program designed to test materials for suitability for use in a fusion reactor. ...

The material of the plasma facing components (PFC) is a special problem. The PFC do not have to withstand large mechanical loads, so neutron damage is much less of an issue. They do have to withstand extremely large thermal loads, up to 10 MW/m², which is a difficult but solvable problem. Regardless of the material chosen, the heat flux can only be accommodated without melting if the distance from the front surface to the coolant is not more than a centimeter or two. The primary issue is the interaction with the plasma. One can choose either a low-Z material, typified by graphite although for some purposes beryllium might be chosen, or a high-Z material, usually tungsten with molybdenum as a second choice. In chemistry and physics, the atomic number (Z) is the number of protons found in the nucleus of an atom. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... General Name, Symbol, Number beryllium, Be, 4 Chemical series alkaline earth metals Group, Period, Block 2, 2, s Appearance white-gray metallic Atomic mass 9. ... In chemistry and physics, the atomic number (Z) is the number of protons found in the nucleus of an atom. ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ...

If graphite is used, the gross erosion rates due to physical and chemical sputtering would be many meters per year, so one must rely on redeposition of the sputtered material. The location of the redeposition will not exactly coincide with the location of the sputtering, so one is still left with erosion rates that may be prohibitive. An even larger problem is the tritium co-deposited with the redeposited graphite. The tritium inventory in graphite layers and dust in a reactor could quickly build up to many kilograms, representing a waste of resources and a serious radiological hazard in case of an accident. The consensus of the fusion community seems to be that graphite, although a very attractive material for fusion experiments, cannot be the primary PFC material in a commercial reactor. Sputtering is a physical process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. ...

The sputtering rate of tungsten can be orders of magnitude smaller than that of carbon, and tritium is not so easily incorporated into redeposited tungsten, making this a more attractive choice. On the other hand, tungsten impurities in a plasma are much more damaging than carbon impurities, and self-sputtering of tungsten can be high, so it will be necessary to ensure that the plasma in contact with the tungsten is not too hot (a few eV rather than tens of eV). Tungsten also has disadvantages in terms of eddy currents and melting in off-normal events, as well as some radiological issues.

Economics

It is far from clear that nuclear fusion will be economically competitive with other forms of power. The many estimates that have been made of the cost of fusion power cover a wide range, and indirect costs of and subsidies for fusion power and its alternatives make any cost comparison difficult. The low estimates for fusion appear to be competitive with but not drastically lower than other alternatives. The high estimates are several times higher than alternatives.

Unfortunately, despite optimism dating back to the 1950's about the wide-scale harnessing of fusion power, there are still significant barriers standing between current scientific understanding and technological capabilities and the practical realization of fusion as an energy source. Research, while making steady progress, has also continually thrown up new difficulties. Therefore it remains unclear that an economically viable fusion plant is even possible.

An important aspect of fusion energy in contrast to many other energy sources is that the cost of production is nearly perfectly elastic. With wind energy, for example, power from the best locations is cheap, but as more generators are installed, poorer sites must be used so the price goes up. With fusion energy, the production cost will not increase much, even if an extremely large number of plants are built. It has been suggested that perhaps even 100 times the current energy consumption of the world is within the realm of possibility. Some problems which are expected to be an issue in the next century such as fresh water shortages can actually be thought of merely as problems of energy supply. For example, in desalination plants, seawater can be converted into pure freshwater through a process of either distillation or reverse osmosis. However, these processes are energy intensive. Even if the first fusion plants are not competitive with alternative sources, fusion could still become competitive if large scale desalination requires more power than the alternatives are able to provide. Ultimately, there is a capacity limit to biofuel, hydro, terrestrial solar, and wind power, which is why some people want research of fusion power in spite of the large costs of such research and the relatively simple and inexpensive nature of other long-term energy solutions. Fusion power has many of the benefits of these long-term energy sources (such as a long-term continuous energy supply and no greenhouse gas emissions) but also some of the benefits of (relatively) short-term energy sources like hydrocarbons and nuclear fission, such as very high power-generation density (i.e. a coal-burning power plant takes up less room than an equivalent power solar power plant) and uninterrupted power delivery (i.e. coal plants work almost entirely independent of the day's weather, unlike wind and solar power). In economics, the price elasticity of demand (PED) is an elasticity that measures the responsiveness of the quantity demanded of a good to its price. ... Water resources are sources of water that are useful or potentially useful to humans. ... Desalination or desalinization refers to any of several processes that remove the excess salt and other minerals from water in order to obtain fresh water suitable for animal consumption or irrigation, and if almost all of the salt is removed, for human consumption, sometimes producing table salt as a by... Sea water is water from a sea or ocean. ... Strathisla whisky distillery in Keith, Scotland Distillation is a method of separation of substances based on differences in their vapor pressures. ... The term reverse osmosis comes from the process of osmosis, the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration if no external pressure is applied. ...

External links

• EURATOM/UKAEA Fusion Association
• ITER
• FIRE
• FUSION FAQ
• European Fusion Development Agreement
• Fusion Power Associates A Washington, DC area lobbying organiation; "a non-profit, tax-exempt research and educational foundation, providing timely information on the status of fusion development." Edits the Journal of Fusion Energy.
• Plasma/Fusion Glossary
• The Helimak Experiment, at the Fusion Research Center at UT Austin
• Investigations of the Formability, Weldability and Creep Resistance of Some Potential Low-activation Austenitic Stainless Steels for Fusion Reactor Applications (ISBN 0853111480):A.H. Bott, G.J. Butterworth, F. B. Pickering
• "Low Activation Material Candidates For Fusion Power Plants"; C.B.A. Forty and N.P. Taylor (PDF format)