Comment on 'Magnetic field effects on gas discharge plasmas' [Phys. Plasmas 13, 063511 (2006)]

N. Sternberg, V. Godyak, and D. Hoffman [Phys. Plasmas 13, 063511 (2006)] have produced a detailed paper on a cylindrical plasma column in an axial magnetic field. The authors found that the radial component of the ion velocity, on leaving the plasma region, is the ion acoustic velocity. This is, of course, the Bohm velocity, but the authors did not comment on this fact. The Bohm criterion does appear to be of general validity, however, and perhaps a greater emphasis should have been given to this result.