Fourier spectrum. Left: fourier decomposition of spatial structure in magnetic field and mass density of charges in the periodic x-direction at t = 612.9 s. For each horizontal mode, n, the amplitudes are calculated and averaged in height over the region of high RTI activity between z = −1.35 Mm and z = 0.65 Mm. Height-averaged Fourier decomposition amplitudes are shown for out-of-plane magnetic field, , in-plane magnetic field, , total magnetic field, B²/μ₀, and mass density of charges, ρ_c. The normalization value (E₀) used for magnetic field data is 10⁻³ J m⁻³ and for ρ_c is 10⁻¹² kg m⁻³. The linear spectral fits ⟨Aⁿ⟩_z ∝ n^Λ for (B²/μ₀) and ρ_c are calculated using a subset of 11 mode amplitude values for n = [5, 7, 10, 13, 18, 25, 35, 48, 66, 91, 126] that are approximately equidistributed over the range of the fit in the log₁₀n space, as illustrated with “x” markers in the panel. Right: time evolution of the spectral exponents. Λ_B and Λ_ρc, during the late non-linear and saturation phases of the RTI calculated at the same time instances as shown in the Fig. 3 snapshots. The errors of the fit are shown as vertical error bars.