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PhD and MPhil Thesis Classes - Université Libre de Bruxelles

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1.7 Plasma Operational LimitsIt is evi<strong>de</strong>nt that smaller values of nτ E correspond to energy losses too severe forself-sustained fusion; larger values could presumably be cured by artificially enhancedlosses. Thus, the Lawson criterion for self-sustained, or “ignited” fusion, states thatthe product of <strong>de</strong>nsity <strong>and</strong> confinement time must equal or exceed (nτ E ) c .The result is sensitive to the particular fusion reaction consi<strong>de</strong>red, as well as tovarious plasma parameters (such as impurity content) that are not easy to predict, sothat a simple general specification is difficult.1.7 Plasma Operational LimitsFigure 1.5: Fusion triple product. The figure is taken from Ref. (2).In recent years there has been consi<strong>de</strong>rable <strong>de</strong>velopment of databases <strong>and</strong> accumulationof knowledge on the behavior of tokamak plasmas around the world. A <strong>de</strong>greeof uncertainty still exists in predicting the confinement properties <strong>and</strong> plasma performancein such a <strong>de</strong>vice. The progress of these researches can be illustrated by the fusionproduct n DT τ E T i , which represents a figure of merit for plasma performance (see figure9

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