The role of the nϕ=1 column mode in spheromak formation

Abstract

Observations in strongly driven spheromak experiments and simulations using a time-dependent, three-dimensional, nonlinear, resistive magnetohydrodynamic code indicate that in the formation phase an nϕ=1 instability (nϕ is the toroidal Fourier mode) is excited by the current-carrying column injected from the gun region. The growth of the nϕ=1 column mode terminates in a violent event in which there is significant magnetic reconnection and a topology change. The combined action of the nϕ=1 kink instability and the reconnection event amplifies the poloidal flux. By means of experimental diagnostics, detailed diagnostics and visualizations in the simulations, and a phenomenological model of the linear perturbations, we investigate the roles of the nϕ=1 column mode and reconnection in forming the spheromak.