a) Initial purely toroidal magnetic configuration. The region of interest is between 0 ≤ ϖ ≲ ϖ₀ given that the field strength falls off at greater ϖ. Colored areas represent surfaces of equal distance to the axis. Field lines are also plotted; their density is related to the increase in the field strength proportional to the distance from the axis. b) Mixed poloidal-toroidal field configuration. The field lines show a spiral morphology, for this particular case (with p = 1) two spirals turns are completed in the box, i.e. toroidal Alfvén frequency is double the vertical Alfvén frequency ω_A,φ = 2ω_A,z.