Electron beam pulses produced by helicon-wave excitation

The 443 nm Ar⁺ line emission intensity in a cylindrical argon magnetoplasma excited by a 13.56 MHz helicon antenna is found to be strongly modulated at the excitation frequency. The peak in optical emission propagates in the axial direction at a velocity corresponding to that of helicon waves launched by the antenna. The spatiotemporal modulation is consistent with pulses of electrons produced by acceleration under the antenna and subsequent entrainment of these electrons over half of a trapping period in the axial electric field of the helicon wave.