Heu = ----
ρ
or
m
Hρ = ----- u
e
Since u is constant, ρ is also constant, i.e. the particle describes a circular orbit of radius ρ. The radius of the circular orbit is thus directly proportional to u, and inversely proportional to H.
If the ion is moving at an angle θ with the direction of the magnetic field, it describes a curve which is compounded of a motion of a particle of velocity u sin θ perpendicular to the field and u cos θ in the direction of the field. The former describes a circular orbit of radius ρ, given by
m
Hρ = --- u sin θ ;