NIFS-305

FULL TEXT (PDF, 390 KB)


Author(s):

T. Hayashi, T. Sato, N. Nakajima, K. Ichiguchi, P. Merkel, J. Nuhrenberg, U. Schwenn, H. Gardner, A. Bhattacharjee and C.C.Hegna

Title:

Behavior of Magnetic Islands in 3D MHD Equilibria of Helical Devices

Date of publication:

Sep. 1994

Key words:

helical system, heliac, heliotron, torsatron, stellarator, three dimensional equilibrium, beta limit, magnetic island, self-healing of magnetic island, finite pressure effect

Abstract:

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-Schluter currents is important. The earlier theory is extended to elucidate the occurrence of the complete self-healing of island when the resistive interchange criterion satisfied.

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