Fourier mode amplitudes (top panels) and growth rates (bottom panels) of B _x in one of the current sheets at times t = 19 τ _c0 (left panels) and t = 37.5 τ _c0 (right panels) in simulation S2K025L. The amplitude was computed with the Fast Fourier Transform via , where N _x , N _y , and N _z are dimensions of the computational grid, and the initial reversing field B ₀ = 0.1 in these units. The components of the wave vector are expressed in units of 2π divided by the computational box size along the relevant direction. We only show growth rates for modes with amplitudes | B _x ( k)| > 10 ⁻⁶.