When a high-energy electron (negative charge) from the discharge cathode hits, or bombards, a propellant atom (neutral charge), a second electron is released, yielding two negative electrons and one positively charged ion. High-strength magnets are placed along the discharge chamber walls so that as electrons approach the walls, they are redirected into the discharge chamber by the magnetic fields. Maximizing the length of time that electrons and propellant atoms remain in the discharge chamber, increases the chances that the atoms will be ionized.