Width of the diffusion region δ_s, and inertial length d_s measured at the center of the diffusion region, for ions and electrons. Panels a) are for the simulation with ω_ce/ω_pe = 3, , T_bg = 1.5 × 10⁷ K and B_G = 0; panels b) for ω_ce/ω_pe = 6, . The phase between 0 and 18T_pe for panels a) (0 and 33T_pe for panels b) corresponds to times where the tearing instability has not yet started. The decrease in δ_e between 18 and 20T_pe for a (33 and 37T_pe for b) is the linear and non-linear growth phase of the instability.