Balancing the centripetal force mv^2/r with the force experienced due to motion in a magnetic field qvB: m = qBr/v = qBC/2piv (C circumference). Putting in numbers: m = 1.83e-23 kg (~11,000 mass of proton at rest!). Energy of beam = Np * 1/2 m v^2 (Np number of protons). Again, using the numbers, we get energy = 2.4e8 J. This is equivalent to the energy a standard car (mass 1.5t) has when traveling at around 1300 mph! (I originally asked this in the question but I went over the character count!).