The Relationship of the n=1 Column Mode to Spheromak Formation

Observations from spheromaks and simulations [1] using the time-dependent, nonlinear, resistive magnetohydrodynamic code NIMROD indicate that in the formation phase an n=1 instability (toroidal Fourier mode) is excited by the current driven down the plasma column by electrostatic current injection into the spheromak. Toroidal harmonics are generated, partly by nonlinear effects; and the growth of the column mode terminates in a violent reconnection event that forms the spheromak: toroidal flux reconnects and poloidal flux emerges. By means of NIMROD simulations, detailed diagnostics, visualizations, and analytical calculations, we investigate the relationship between the n=1 column mode and the reconnection event that forms the spheromak. [1] C. R. Sovinec, B. I. Cohen, et al., Phys. Rev. Lett. 94, 035003 (2005); B.I. Cohen, E.B. Hooper, et al., Phys. Plasmas 12, 056106 (2005); E. B. Hooper, B. I. Cohen, et al., J. Fusion Energy 26, 71 (2007); E. B. Hooper, B. I. Cohen, et al., Phys. Plasmas 15, 032502 (2008).