An ion beam is rapidly switched off during ion implantation on detecting a beam instability. The ion beam is generated or provided by a non-arc discharge based ion source, such as an electron gun ion source or an RF ion source. The ion beam is scanned across a workpiece from a starting location toward an ending location. During the scanning, one or more beam characteristics are monitored, such as beam current, beam flux, shape, and the like. An instability is detected when one or more of the beam characteristics deviate from acceptable values or levels. The ion beam is rapidly turned off on the detected instability.