Two propagating modes of low-frequency waves in a single-ended Q machine

Two propagating modes of low-frequency perturbations are excited by applying oscillating currents to a small coil surrounding a plasma column in a single-ended Q machine. One of them has the same phase velocity and damping factor as grid-excited waves, in spite of quite different exciting mechanisms. The other is observed to propagate only when the exciting frequency is higher than the frequency slightly above the ion cyclotron frequency. Its phase velocity increases with an increase in the magnetic field. This mode follows a dispersion relation of electrostatic ion cyclotron waves propagating along a magnetized plasma column.