Image: CubeSat micro-pulsed plasma thruster
(PHYSorg.com Space & Earth)

This micro-pulsed plasma thruster has been designed for propulsion of miniature CubeSats; its first firing is seen here. The thruster works by pulsing a lightning-like electric arc between two electrodes. This vaporizes the thruster propellant into charged plasma, which is then accelerated in the electromagnetic field set up between the electrodes.