Maximum Lorentz factor of dust grains with a = 5 × 10⁻⁷ cm for various grain average atomic weight and potential. The thickness of the lines accounts for the change in potential (from 1 V to 100 V). The black, red, and blue lines correspond, respectively, to a magnetic field amplified due to the growth of non-resonant streaming instabilities (Bell), to a fixed value of 100 μG, and to a fixed value of 3 μG. The solid lines assume a mean mass μ = 5, and the dashed lines μ = 56.