In a cyclotron, a charged particle

Inside the dees of a cyclotron, a uniform magnetic field acts perpendicular to the velocity of the charged particle. This magnetic field provides the necessary centripetal force, causing the particle to move in a circular path. Since the direction of velocity continuously changes, the particle experiences centripetal acceleration.

In the gap between the dees, an oscillating electric field is present. This electric field increases the speed (and kinetic energy) of the particle, which is also a form of acceleration (tangential acceleration).

Therefore, the charged particle undergoes acceleration all the time.

Answer: undergoes acceleration all the time.