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The temporal evolution of the current-driven electrostatic ion cyclotron instability was investigated experimentally. The critical destabilizing electron drift velocity for different values of mode phase velocity was measured. The phase velocity was changed by varying the effective plasma column length and hence the parallel wavelength. Ion cyclotron damping was observed to dominate over electron Landau damping at low phase velocities. The temporal growth rate was experimentally determined for several values of electron drift and found to agree very well with linear theory. The observed saturated mode amplitudes compare favorably with the saturation levels predicted by a theory of nonlinear stabilization due to wave induced collisions.

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Ion-cyclotron waves are excited by a cesium ion beam in a cesium Q-machine plasma with drifting plasma electrons. These interactions differ significantly from those in the case of drifting ions in that the drifting electrons play an active role in the instability mechanism. The observed mode frequencies are slightly below those of the electron current driven modes. These waves can be convectively or absolutely unstable, depending on the ion beam velocity. For low beam velocities the instabifities are convective in character with large spatial growth rates ki/kr ∼ 0.2. For larger beam velocities the instabilities are absolute in character with temporal growth rates 0.04. The absolute instabilities are similar to two-stream instabilities. Plasma ion heating is observed and is consistent with a model in which mode amplitudes are saturated by diffusion effects.

High-re solution tunable laser resonance diagnostics reveal ion density decreases within the unstable region of an ion-cyclotron wave as well as hot-ion transport out of the unstable region, showing that instability and heating are dominated by a nonlocal process combining ion transport with heating.