The fusion reaction rate increases rapidly with temperature until it maximizes and then gradually drops off. The deuterium-tritium fusion rate peaks at a lower temperature (about 70 keV, or 800 million kelvin) and at a higher value than other reactions commonly considered for fusion energy. The basic concept behind any fusion reaction is to bring two or more nuclei close enough together so that the residual strong force (nuclear force) in their nuclei will pull them together into one larger nucleus. If two light nuclei fuse, they will generally form a single nucleus with a slightly smaller mass than the sum of their original masses (though this is not always the case). The difference in mass is released as energy according to Albert Einstein's mass-energy equivalence formula E = mc2. If the input nuclei are sufficiently massive, the resulting fusion product will be heavier than the sum of the reactants' original masses, in which case the reaction requires an external source of energy. The dividing line between "light" and "heavy" is iron-56. Above this atomic mass, energy will generally be released by nuclear fission reactions; below it, by fusion.[5] Fusion between the nuclei is opposed by their shared electrical charge, specifically the net positive charge of the protons in the nucleus. To overcome this electrostatic force, or "Coulomb barrier", some external source of energy must be supplied. The easiest way to do this is to heat the atoms, which has the side effect of stripping the electrons from the atoms and leaving them as bare nuclei. In most experiments the nuclei and electrons are left in a fluid known as a plasma. The temperatures required to provide the nuclei with enough energy to overcome their repulsion is a function of the total charge, so hydrogen, which has the smallest nuclear charge therefore reacts at the lowest temperature. Helium has an extremely low mass per nucleon and therefore is energetically favoured as a fusion product. As a consequence, most fusion reactions combine isotopes of hydrogen ("protium", deuterium, or tritium) to form isotopes of helium (3 He or 4 He). The reaction cross section, denoted σ, is a measure of the probability of a fusion reaction as a function of the relative velocity of the two reactant nuclei. If the reactants have a distribution of velocities, as is the case in a thermal distribution within a plasma, then it is useful to perform an average over the distributions of the product of cross section and velocity. The reaction rate (fusions per volume per time) is <σv> times the product of the reactant number densities: ƒ = (½n)2 <σv> (for one reactant) ƒ = n1n2 <σv> (for two reactants) <σv> increases from virtually zero at room temperatures up to meaningful magnitudes at temperatures of 10–100 keV (2.2–22 fJ). The significance of <σv> as a function of temperature in a device with a particular energy confinement time is found by considering the Lawson criterion. Perhaps the three most widely considered fuel cycles are based on the D-T, D-D, and p-11 B reactions.[citation needed] Other fuel cycles (D-3 He and 3 He-3 He) would require a supply of 3He, either from other nuclear reactions or from extraterrestrial 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. [edit] D-T fuel cycle Diagram of the D-T reaction The easiest (according to the Lawson criterion) and most immediately promising nuclear reaction to be used for fusion power is: 2 1D + 3 1T → 4 2He + 1 0n Hydrogen-2 (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. Hydrogen-3 (Tritium) is also an isotope of hydrogen, but it occurs naturally in only negligible amounts due to its radioactive half-life of 12.32 years. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions: 1 0n + 6 3Li → 3 1T + 4 2He 1 0n + 7 3Li → 3 1T + 4 2He + 1 0n The reactant neutron is supplied by the D-T fusion reaction shown above, the one that 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 reacThe fusion reaction rate increases rapidly with temperature until it maximizes and then gradually drops off. The deuterium-tritium fusion rate peaks at a lower temperature (about 70 keV, or 800 million kelvin) and at a higher value than other reactions commonly considered for fusion energy. The basic concept behind any fusion reaction is to bring two or more nuclei close enough together so that the residual strong force (nuclear force) in their nuclei will pull them together into one larger nucleus. If two light nuclei fuse, they will generally form a single nucleus with a slightly smaller mass than the sum of their original masses (though this is not always the case). The difference in mass is released as energy according to Albert Einstein's mass-energy equivalence formula E = mc2. If the input nuclei are sufficiently massive, the resulting fusion product will be heavier than the sum of the reactants' original masses, in which case the reaction requires an external source of energy. The dividing line between "light" and "heavy" is iron-56. Above this atomic mass, energy will generally be released by nuclear fission reactions; below it, by fusion.[5] Fusion between the nuclei is opposed by their shared electrical charge, specifically the net positive charge of the protons in the nucleus. To overcome this electrostatic force, or "Coulomb barrier", some external source of energy must be supplied. The easiest way to do this is to heat the atoms, which has the side effect of stripping the electrons from the atoms and leaving them as bare nuclei. In most experiments the nuclei and electrons are left in a fluid known as a plasma. The temperatures required to provide the nuclei with enough energy to overcome their repulsion is a function of the total charge, so hydrogen, which has the smallest nuclear charge therefore reacts at the lowest temperature. Helium has an extremely low mass per nucleon and therefore is energetically favoured as a fusion product. As a consequence, most fusion reactions combine isotopes of hydrogen ("protium", deuterium, or tritium) to form isotopes of helium (3 He or 4 He). The reaction cross section, denoted σ, is a measure of the probability of a fusion reaction as a function of the relative velocity of the two reactant nuclei. If the reactants have a distribution of velocities, as is the case in a thermal distribution within a plasma, then it is useful to perform an average over the distributions of the product of cross section and velocity. The reaction rate (fusions per volume per time) is <σv> times the product of the reactant number densities: ƒ = (½n)2 <σv> (for one reactant) ƒ = n1n2 <σv> (for two reactants) <σv> increases from virtually zero at room temperatures up to meaningful magnitudes at temperatures of 10–100 keV (2.2–22 fJ). The significance of <σv> as a function of temperature in a device with a particular energy confinement time is found by considering the Lawson criterion. Perhaps the three most widely considered fuel cycles are based on the D-T, D-D, and p-11 B reactions.[citation needed] Other fuel cycles (D-3 He and 3 He-3 He) would require a supply of 3He, either from other nuclear reactions or from extraterrestrial 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. [edit] D-T fuel cycle Diagram of the D-T reaction The easiest (according to the Lawson criterion) and most immediately promising nuclear reaction to be used for fusion power is: 2 1D + 3 1T → 4 2He + 1 0n Hydrogen-2 (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. Hydrogen-3 (Tritium) is also an isotope of hydrogen, but it occurs naturally in only negligible amounts due to its radioactive half-life of 12.32 years. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions: 1 0n + 6 3Li → 3 1T + 4 2He 1 0n + 7 3Li → 3 1T + 4 2He + 1 0n The reactant neutron is supplied by the D-T fusion reaction shown above, the one that 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 reac

The fusion reaction rate increases rapidly with temperature until it maximizes and then gradually drops off. The deuterium-tritium fusion rate peaks at a lower temperature (about 70 keV, or 800 million kelvin) and at a higher value than other reactions commonly considered for fusion energy.

The basic concept behind any fusion reaction is to bring two or more nuclei close enough together so that the residual strong force (nuclear force) in their nuclei will pull them together into one larger nucleus. If two light nuclei fuse, they will generally form a single nucleus with a slightly smaller mass than the sum of their original masses (though this is not always the case). The difference in mass is released as energy according to Albert Einstein's mass-energy equivalence formula E = mc². If the input nuclei are sufficiently massive, the resulting fusion product will be heavier than the sum of the reactants' original masses, in which case the reaction requires an external source of energy. The dividing line between "light" and "heavy" is iron-56. Above this atomic mass, energy will generally be released by nuclear fission reactions; below it, by fusion.^[5]
Fusion between the nuclei is opposed by their shared electrical charge, specifically the net positive charge of the protons in the nucleus. To overcome this electrostatic force, or "Coulomb barrier", some external source of energy must be supplied. The easiest way to do this is to heat the atoms, which has the side effect of stripping the electrons from the atoms and leaving them as bare nuclei. In most experiments the nuclei and electrons are left in a fluid known as a plasma. The temperatures required to provide the nuclei with enough energy to overcome their repulsion is a function of the total charge, so hydrogen, which has the smallest nuclear charge therefore reacts at the lowest temperature. Helium has an extremely low mass per nucleon and therefore is energetically favoured 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).
The reaction cross section, denoted σ, is a measure of the probability of a fusion reaction as a function of the relative velocity of the two reactant nuclei. If the reactants have a distribution of velocities, as is the case in a thermal distribution within a plasma, then it is useful to perform an average over the distributions of the product of cross section and velocity. The reaction rate (fusions per volume per time) is <σv> times the product of the reactant number densities:

ƒ = (½n)² <σv> (for one reactant)

ƒ = n₁n₂ <σv> (for two reactants)

<σv> increases from virtually zero at room temperatures up to meaningful magnitudes at temperatures of 10–100 keV (2.2–22 fJ). The significance of <σv> as a function of temperature in a device with a particular energy confinement time is found by considering the Lawson criterion.
Perhaps the three most widely considered fuel cycles are based on the D-T, D-D, and p-11B reactions.^{[citation needed]} Other fuel cycles (D-3He and 3He-3He) would require a supply of ³He, either from other nuclear reactions or from extraterrestrial 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.

[edit] D-T fuel cycle

Diagram of the D-T reaction

The easiest (according to the Lawson criterion) and most immediately promising nuclear reaction to be used for fusion power is:

2 1D + 3 1T → 4 2He + 1 0n

Hydrogen-2 (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. Hydrogen-3 (Tritium) is also an isotope of hydrogen, but it occurs naturally in only negligible amounts due to its radioactive half-life of 12.32 years. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions:

1 0n + 6 3Li → 3 1T + 4 2He

1 0n + 7 3Li → 3 1T + 4 2He + 1 0n

The reactant neutron is supplied by the D-T fusion reaction shown above, the one that 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 reactor