Design of a 15-MeV CW Microtron

With the above-described adjustments a CW microtron should be realizable producing an output energy of 15 MeV in 39 turns. The salient design characteristics of this machine are listed in Table II and the early orbits are plotted in Figure 3. An investigation of the dependence of orbit stability on the angle of injection shows that this is critical. For the chosen conditions electrons injected more than 1° from the assigned input beam direction (10° to the cavity axis) mill not be accepted into stable orbits. Thus an electron gun is necessary which will provide a large current within a very small angular spread. In addition, deviations from the chosen entering phase angle of more than half a degree will result in the subsequent orbits being unstable. The accelerator thus starts off by reducing the intensity of the beam injected into the cavity from the cathode by a factor of 360. Nevertheless, with an efficient electron gun and good homogeneity in the magnetic field, final beam currents approaching 100 ¿a should be obtainable.