Comment on “Weakly collisional Landau damping and three-dimensional Bernstein–Greene–Kruskal modes: New results on old problems” [Phys. Plasmas 13, 055903 (2006)

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In their paper on two-dimensional/three-dimensional 2D/3D Bernstein–Greene–Kruskal BGK modes, Ng et al. made a couple of very brief references to my 2005 paper on BGK modes in a magnetized plasma Ref. 2 , referring it with others as one with gyrokinetic solutions of 3D BGK for a “strong B” their characterization of the fact that the solution breaks down when B is sufficiently weak . They did not reference my 2002 work, which earlier analyzed BGK modes in a magnetized plasma with unexplicable typographical error subsequently noted , an analysis which was expanded in my 2005 paper. Furthermore, while Ng et al. did not specify the meaning of strong B, in both references to Ref. 2 they immediately lumped it in with their discussion of the published B→ analyses. In fact, the strong-B solutions presented in Ref. 2 are clearly more general than the B→ case and only reduce to that one-dimensional 1D case when the limit B→ is specifically taken in the general solutions derived. The claim is incorrect in the later discussion of their paper when, in referring to these ”strong-B” solutions, they claimed that the “physical reason such solutions exist is related to the 1D aspect of the theory.” Furthermore, for the 3D strong-B solutions I derived an angular criterion with respect to the magnetic field direction for the existence of magnetized BGK modes,