The magnetic force acting on the proton is
where
q is the proton charge
v is its speed
B is the intensity of the magnetic field
is the angle between the direction of v and B; since the proton is moving perpendicular to the magnetic field, 
and 
, so the force becomes
this force provides the centripetal force that keeps the proton in circular motion:
where the term on the left is the centripetal force, with
m being the mass of the proton
r the radius of its orbit
Re-arranging the previous equation, we can find the radius of the proton's orbit:
And now we can calculate the centripetal acceleration of the proton, which is given by
where
q is the proton charge
v is its speed
B is the intensity of the magnetic field
this force provides the centripetal force that keeps the proton in circular motion:
where the term on the left is the centripetal force, with
m being the mass of the proton
r the radius of its orbit
Re-arranging the previous equation, we can find the radius of the proton's orbit:
And now we can calculate the centripetal acceleration of the proton, which is given by
