Charged particles experience a force normal to their motion,which may be a reason for their circular path around a centre.Cyclotrons are those machinaries that accelerate the charged particles outwards the field in a spiral path and thereby exciting the particle.
Cyclotrons are used in researches to study about EM waves,and to study the properties of nucleus of an atom in nuclear physics.
Apart from researches,they are used in particle therapy like cancer ,wherein the radiations are used to penetrate body tissues and damage cancer cells ,senescent cells,etc.