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Elongation

(Science: radiobiology) parameter indicating the degree to which the cross-section of a toroidal plasma is non-circular. Kappa=b/a, where b and a are the vertical and horizontal minor radii. As kappa is increased, the confinement in relation to the total current improves, but the plasma also becomes more and more unstable to vertical displacements. A circular plasma has kappa of 1, a common value for elongated plasmas is 1.7, and the absolute limit is probably around 2.