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On the destruction of islands of stability in a tokamak with ergodic magnetic limiter using KAM theory

Mosoud Jazayeri, Ahmadreza Sohrabi
Abstract. Chaotic magnetic field lines play an important role in plasma confinement by tokamaks. They can
either be generated in the plasma as results of natural instabilities or artificially produced by external conductors
like ergodic magnetic limiter (EML). We consider a symplectic map for magnetic field lines in a tokamak with an
ergodic limiter the nature of fixed points of EML map are studied in detail as perturbation parameter p and
magnetic shear s are varied. The critical perturbation is determined for the surface with rotational-transform equal
to the inverse golden mean. We describe the changes and the destruction of islands of stability for EML map. As
the perturbation parameter increases the size of the island increases and then decreases abruptly. This decrease is
due to the joining of an outer and inner chaotic domain. Critical value of the limiter strength p necessary to global
chaos for the secondary islands as a function of the magnetic shear s is obtained.
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