Cyclotron resonance describes the interaction of external forces with charged particles experiencing a magnetic field, thus already moving on a circular path. It is named after the cyclotron, a cyclic particle accelerator that utilizes an oscillating electric field tuned to this resonance to add kinetic energy to charged particles.
The cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicular to the direction of a uniform magnetic field B (constant magnitude and direction). Since that motion is always circular, the cyclotron frequency is given by equality of centripetal force and magnetic Lorentz force
with the particle mass m, its charge q, velocity v, and the circular path radius r, also called gyroradius.
By substitution for the circulation frequency which defines the cyclotron frequency, this leads to
or the angular frequency
It is notable that the cyclotron frequency is independent of the radius and velocity and therefore independent of the particle's kinetic energy.