Relativistic electron beams (REBs) are streams of electrons
moving at relativistic
speeds. They are the lasing medium in free electron lasers
(FELs) to be used in atmospheric research conducted at such entities as the Pan-oceanic Environmental and Atmospheric Research Laboratory (PEARL) at the University of Hawaii
It has been suggested that REBs could be used to heat and accelerate the reaction mass in electrical rocket engines that Dr. Robert W. Bussard called Quiet Electric Discharge Engines (QEDs).