Modeling of magnetic island formation in magnetic reconnection experiment

Formation of a magnetic island found in the Magnetic Reconnection Experimen t (MRX) [M. Yamada, H. Ji, S. Hsu, et al., Phys. Plasmas 4, 1936 (1997)] is investigated by a magnetohydrodynamic (MHD) relaxation theory and a numeri cal simulation. In the cohelicity injection with a mean toroidal field, the growing process of the island into a spheromak-type configuration is expla ined by quasistatic transition of the force-free and minimum energy state t o a state with larger normalized helicity. It also turns out that no magnet ic island would be generated in the counterhelicity case. The MHD simulatio n with inhomogeneous electric resistivity agrees with experimental results, which clearly shows formation and growth of the magnetic island in a diffu sion region where the reconnection takes place. (C) 1999 American Institute of Physics. [S1070-664X(99)03904-X].