English: The Pilot Plasma Engine. This traveling wave accelerator, being operated by Raymond W. Plamer of the Lewis Electromagnetic Propulsion Division, uses an alternating current power supply. The AC feature avoids the life limitations of direct current accelerators where electrode parts rapidly deteriorate from touching the plasma. The traveling wave accelerator works like its name. A neutral plasma of electrons and ions is produced in the source at the left. This plasma moves to the right and is accelerated by a moving magnetic field in the four black coils. Such acceleration produces thrust, perhaps enough to propel a future spacecraft beyond the Moon.