An ion-acceleration mechanism is proposed in which ions are trapped and accelerated by a negative-energy space-charge wave. Under certain conditions, an electron beam propagating down a slowly converging metal guide can be accelerated. A low-phase-velocity space-charge wave initiated at the large-radius end of the guide, because it is supported by the beam, will also accelerate. By trapping ions in the potential wells of a low-phase-velocity wave, ion acceleration down the converging drift tube can be achieved.

• Received 20 October 1975

DOI:https://doi.org/10.1103/PhysRevLett.36.1180