Saturated spectra of right-handed waves (I₊; top panel) and of left-handed waves (I₋; bottom panel). Lines of different colour correspond to different mass ratio adopted in the simulations: blue line corresponds to m_i/m_e = 1000 (Fid run), red line corresponds to 400, and orange line corresponds to 100. Inset: cut-off wavenumber of left-handed branch for different values of m_i/m_e. Blue circles correspond to values derived from simulations with n_cr/n_i = 10⁻² and red circles are from simulations with n_cr/n_i = 5 × 10⁻³. The dashed black line follows k_cutd_i = 0.5.