Magnetic field effects on secondary electrons emitted during ion implantation in vacuum arc plasmas

Aluminum ions produced in a vacuum arc system with a straight magnetic duct were implanted in a copper sample oriented with its surface parallel to the plasma stream and magnetic field. One Faraday cup measured the secondary electrons emitted normally to the sample's surface, while another cup was oriented to detect electrons that flow along the field lines. Large negative spikes coincident with high voltage pulses are seen in the perpendicular cup's current when the field is absent. These spikes correspond to emitted secondary electrons as shown by their energies, measured by operating the cup as a retarding potential analyzer. A secondary electron emission coefficient of 0.53 was measured at -2.5 kV. When a 12.5 mT magnetic field is applied, these spikes are not seen, neither in the perpendicular cup's current, showing that secondary electrons were magnetically suppressed, nor in the longitudinal cup's current, indicating that a virtual cathode was formed near the electrode's surface