Beam loss due to the vr - vz = 1 and 3vr - vz = 3 resonances

In the Oak Ridge Isochronous Cyclotron (ORIC) there had been unexplained beam loss when protons were accelerated to maximum energy. Since recent successes in computing trim-coil currents lend assurance that the magnetic field is reasonably isochronous, the computed orbit properties can now be compared with the observed beam behavior. The orbit properties computed for proton acceleration indicate that the 60-MeV beam passes through the v_r - v_z =l resonance; computed and measured radii for beam loss are in excellent agreement. Computations also show that the beam is passing through, and in some cases closely following, the essential resonance 3v_r - v_z = 3. Under certain operating conditions where it had been very difficult to accelerate the beam to full radius, the valley coils (which can vary the axial focusing strength over a wide range) can now be adjusted so as to avoid the v_r - v_z = 1 coupling resonances and allow acceleration of the beam to full radius without significant beam loss.