Unstable electrostatic ion cyclotron waves excited by an ion beam

Abstract
Electrostatic ion cyclotron waves were observed in a quiescent cesium plasma into which a low-energy beam of sodium ions was injected. The instability appeared when the beam velocity was above 12 times the ion thermal velocity. The waves propagated along the magnetic field with a velocity somewhat smaller than that of the beam. The dispersion relation was in good agreement with theory.