An accelerator for accelerating two beams of charged particles and for producing a collision of the beams includes: an apparatus for producing an electrostatic potential field such that the two beams are acceleratable or deceleratable by the electrostatic field, a reaction zone for collision of the charged particles; first and second acceleration distances for the first and second beams, each acceleration distance directed towards the reaction zone, wherein the reaction zone is arranged geometrically with respect to the potential field and to the acceleration distances such that the particles of the beams are acceleratable towards the reaction zone along the first and second acceleration distances and, after interaction in the reaction zone and passage through the reaction zone, are deceleratable in the potential field, such that energy used by the potential field apparatus for accelerating the beams towards the reaction zone can be at least partially recovered by the deceleration.