The Collaborative International Dictionary of English v.0.48:

betatron \be"ta*tron\ n.
   a type of particle accelerator which accelerates a continuous
   beam of electrons to high speeds by means of the electric
   field produced by changing magnetic flux.

   Syn: induction accelerator.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

betatron
    n 1: accelerates a continuous beam of electrons to high speeds
         by means of the electric field produced by changing
         magnetic flux [syn: betatron, induction accelerator]