Amplification of magnetic fields. In panel a, the total magnetic energy is shown as a function of time on a logarithmic scale (blue) and on a linear scale (orange). Panels b, c, d, e: the sonic Mach number, the ratio of the wavelength of the fastest growing MRI mode and the AREPO cell size (λ_MRI/l_cell), and the absolute magnetic-field strength (|B|) in the orbital plane, respectively. They provide details of the two episodes of field amplification: at t = 352 d, marked with black dots, and at t = 1504 d, indicated with red dots.