The propellant used in this technique is xenon, a heavy inert gas. The energy, which propels the xenon jet, is the electrical energy from solar cells. This electricity is supplied to both the ionization chamber and to the neutralizer at the nozzle of the rocket.
The propellant is pumped into the ionization chamber where the propellant atoms get ionized.
The process takes place as follows:
Ionization is done by electron bombardment of the neutral atoms. Positive ions are produced by electron bombardment of neutral propellant atoms in a discharge chamber. The impact of an electron on a xenon atom knocks away one of xenon's 54 electrons. This results in a xenon atom with a positive charge, or what is known as an ion.
The exhaust of the rocket must be neutral. That is because, if only positive ions are emitted, the knocked off electrons are left behind and the spacecraft becomes negatively charged. So after a certain amount of time, the spacecraft would attract all the emitted positive ions and the propulsion system would not do its function of creating thrust. In order to ensure that exhaust is neutral, neutralizer emits exactly the same number of electrons into the ion stream (exhaust), as there are ions. This prevents the spacecraft from charging to a large negative potential.