Parametric excitation of equilibrium surface ripples on magnetically confined nonneutral plasma columns

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Abstract
The parametric excitation of equilibrium surface ripples on a drifting, magnetically confined nonneutral plasma column is investigated by passing it through a spatially periodic magnetic field. Measurements of the relationship between the ripple amplitude and the pump frequency, the number of pump periods, and the pump amplitude verify most of the features predicted theoretically. Measurements also verify the predicted relationship between the rigid rotor angular velocity of the plasma column and the amplitude of these equlibrium ripples. Rotation of the column opposite to the direction that an isolated electron would gyrate in the same magnetic field and rotation at an angular velocity greater than the cyclotron frequency are observed. The relation between the ripple amplitude and the propagation characteristics of space-charge waves is discussed.