MAGNETOHYDRODYNAMIC SIMULATION ON CO-HELICITY AND COUNTER-HELICITY MERGING OF SPHEROMAKS AND DRIVEN MAGNETIC RECONNECTION

A magnetohydrodynamic relaxation process of spheromak merging is studi ed by means of an axisymmetric numerical simulation. As a result of co unter-helicity merging, a field-reversed configuration is obtained in the final state, while a larger spheromak is formed after co-helicity merging. In the counter-helicity case, a clear pressure profile of whi ch iso-surfaces coincide with flux surfaces is generated by thermal tr ansport of a poloidal flow induced by driven reconnection. It is also found that a sharp pressure gradient formed in the vicinity of a recon nection point causes a bouncing motion of spheromaks. According to the bounce motion, the reconnection rate changes repeatedly. As shown by the Tokyo University Spherical Torus No. 3 (TS-3) experiments [M. Yama da, et al., Phys. Rev. Lett. 65, 721 (1990)], furthermore, strong acce leration of a toroidal flow and reversal of a toroidal field in the co unter-heIicity merging were observed. (C) 1997 American Institute of P hysics.