Effective turbulence coefficient α_eff as a functionof β_mag for gas of density of n_⟨H⟩ = 10¹⁰ cm⁻³ and 10¹² cm⁻³ at T = 100 K in a disk midplane. The minimum free electron abundance is 10⁻³ with respect to the total number of negative charges (i.e., all the other charges are on dust grains). Left panels: ideal-MHD, ohmic, and ambipolar diffusion contributions to α_eff, while two right panels: resulting α_eff including the all-mode damping criterion of Jin (1996). Lines at 10⁻¹⁰ in the right panels mean no MRI-driven turbulence for a total ionization fraction of 10⁻¹¹ for all values of β_mag.