Parametric Excitation of Nonneutral-Plasma Surface Ripples

Parametric excitation of the equilibrium surface ripples of a drifting, magnetically confined, nonneutral plasma is investigated by passing it through a spatially periodic magnetic field. Resonances are observed at $2{\Omega }_0$, ${\Omega }_0$, and $\frac{{\Omega }_0}{2}$ (${\Omega }_0$ is the natural frequency for the ripple). The ripple amplitude of the equilibrium surface is measured as a function of the phase angle of the excitation, the number of pump periods, and the magnitude of the magnetic field perturbations.