cyclotron is used to accelerate charged particles to very high frequencies by making it to pass through a moderate electric field a no. of times .....the perpendicular magnetic field makes it to oscillate ......as u knw it consist of two metallic dees ... D1 & D2 ...a charged particle like alpha particle is placed in between the gap of two dees ...when charged particle reaches D1 then for it D1 is +ve and D2 is -ve ...so starts accelerating towards it... when it reaches D2 for it D2 IS +ve &there is no electric field there due to the poor shielding effect of metallic dees .....as soon as the electric feild is applied ..it finds AGAIN D2 to be -ve & start accelerating towards it...in this way charged particles come in motion &after attaining high energies it get ejected by window pane ...
this is the working of cyclotron ...
ihope u will be bebefitted by my answer