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In nuclear fusion research, the Lawson criterion, first derived on fusion reactors (initially classified) by John D. Lawson in 1955 and published 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 is sufficient to maintain the temperature of the plasma against all losses without external power input. As originally formulated the Lawson criterion gives a minimum required value for the product of the plasma (electron) density ''n''e and the "energy confinement time" . Later analysis suggested that a more useful figure of merit is the "triple product" of density, confinement time, and plasma temperature ''T''. The triple product also has a minimum required value, and the name "Lawson criterion" often refers to this inequality. == Energy Balance == The central concept of the Lawson criterion is the energy balance for any fusion power plant, using a hot plasma. This is shown below: Net Power = Efficiency × (Fusion − Radiation Loss − Conduction Loss) #Net Power is the net power for any fusion power plant. #Efficiency how much energy is needed to drive the device and how well it collects power. #Fusion is rate of energy generated by the fusion reactions. #Radiation is the energy lost as light, leaving the plasma. #Conduction is the energy lost, as mass leaves the plasma. Lawson calculates the fusion rate by assuming that any fusion reactor contains a hot plasma cloud which has a Gaussian curve of energy. Based on that assumption, he estimates the first term, the fusion energy coming from a hot cloud using the volumetric fusion equation.〔Lyman J Spitzer, "The Physics of Fully Ionized Gases" 1963〕 Fusion = Number Density of Fuel A × Number Density of Fuel B × Cross Section(Temperature) × Energy Per Reaction #Fusion is the rate of fusion energy produced by the plasma #Number density (particles per unit volume) is the density of the respective fuels (or just one fuel, in some cases). #Cross Section is a measure of the probability of a fusion event, based on plasma temperature #Energy per reaction is the energy made in each fusion reaction This equation is typically averaged over a population of ions which has a normal distribution. For his analysis, Lawson ignores conduction losses. In reality this is nearly impossible, practically all systems lose energy through mass leaving. Lawson then estimated〔 the radiation losses using the equation below. where ''N'' is the number density of the cloud and ''T'' is the temperature. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lawson criterion」の詳細全文を読む スポンサード リンク
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