A 200-eV electron beam is incident on an electrode in a laboratory plasma. The emission of secondary electrons produces a region of negative differential resistance in the current-voltage characteristic of the electrode. Spontaneous dynatron oscillations are driven by the negative differential resistance when a resonant circuit is placed in series with the electrode. The instability is driven by the beam energy, produces large amplitudes comparable to the beam voltage, modulates beam and plasma parameters, and excites plasma eigenmodes such as ion acoustic waves.

• Received 29 June 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.556