Cyclotron motion in a uniform magnetic field

What you are seeing: a charged particle (q = m = 1) in a uniform out-of-page magnetic field B. The Lorentz force $\mathbf{F} = q \mathbf{v} \times \mathbf{B}$ is always perpendicular to $\mathbf{v}$, so it does no work; the speed is constant. The trajectory is a circle of radius $r = m v / (q B)$ traced at angular frequency $\omega_c = q B / m$. Increasing $B$ tightens the orbit but speeds up the rotation, leaving the period $T = 2\pi m / (q B)$ shorter.

Vary $B$: smaller $B$ gives bigger circles. Vary the initial speed: at fixed $B$, larger $v$ gives bigger circles but the same period. The field-strength readout shows the resulting radius and period.