syn·chro·cy·clo·tron 
(sĭng′krō-sīklə-trŏn′, sĭn′-)
(sĭng′krō-sīklə-trŏn′, sĭn′-)n.
A cyclotron that modulates the frequency of the electric fields that accelerate a particle, thereby synchronizing the accelerating forces with the particle as its relativistic mass increases with velocity.