Behavior of magnetic islands in 3D MHD equilibria of helical devices

摘要

Magnetic island formation in three-dimensional finite-(beta) equilibria in the H-1 Heliac is studied by using the HINT code. It is found that the size of a dangerous island should increase with (beta) but that a destruction of the equilibrium at low (beta) is avoided because the rotational transform evolves to exclude the rational surface concerned. At higher (beta) there is evidence of near-resonant flux surface deformations which may lead to an equilibrium limit. A reconnected equilibrium at still higher (beta) exhibits a double island structure which is similar to homoclinic phase portraits which have been observed after separatrix reconnection in Hamiltonian systems. Physical mechanism of the island formation in finite-(beta) helical equilibria is investigated to confirm there are cases where the global effect of the Pfirsch-Schlueter currents is important. The earlier theory is extended to elucidate the occurence of the complete self-healing of island when the resistive interchange criterion satisfied. (author). (ERA citation 20:014523)