Spontaneous Dynamics of Magnetic Islands Depending on Plasma Parameters in LHD

Spontaneous dynamics of magnetic islands depending on various plasma parameters in the Large Helical Device (LHD) are described. The structure of the magnetic island undergoes deformation during a discharge. There are two states of magnetic island; they are the growth and self-healing of the magnetic island. The self-healing occurs in the higher-beta and lower-collisionality plasmas. The magnetic island, on the other hand, grows in the lower-beta and higher-collisionality region. The self-healing phenomenon is realized by the disappearance of the local flattening of the T_e profile and the perturbed magnetic field structure compensating the externally imposed perturbation field to produce a seed magnetic island.