Evolution of magnetic field distributions during the core hydrogen-burning phase for the inner 0.34 M_⊙ region of a 1.5 M_⊙ magneto-rotational star, for five different epochs, which are indicated by the legends. In this test case, magnetic dissipation by the η effect is included and accounts for the short timescale evolution. Top panel: radial component of the field, B_r. Middle panel: the toroidal component, B_ϕ, is shown for a case in which only the diffusion term of the magnetic dissipation is included. Meanwhile, B_ϕ evolution for a case with both diffusion and advection terms of the magnetic dissipation is shown in the bottom panel.