The magnetic force = Fm = i l X B on the proton beam.
= vector cross product of length of conductor and magnetic field
Magnitude of Fm = i l B sin Ф where
i = current in conductor, l = lenght of conductor facing magnetic field
B = magnetic field , Ф = angle between conductor & mag. field
Direction is perpendicular to conductor & mag. field. Use right hand thumb rule.
If, Ф = 0, ie., conductor is along the direction of field, then Force = 0.
Magnetic force depends on current in conductor and lenght of conductor , magnetic field strenght, and angle between conductor and mag field.