Stationary modes in a non-neutral plasma

In a non-neutral plasma column of constant density it is shown that, for certain parameter values, an infinitely degenerate internal mode, which has no variation in the axial direction, can be stationary in the laboratory frame. However, this mode cannot be driven resonantly by stationary electric or magnetic field asymmetries. When the plasma density is nonuniform the possibility of resonance of stationary field asymmetries with the continuous spectrum is pointed out. (C) 1998 American Institute of Physics.