Production of tightly focused e-beams with high-current accelerators

Using numerical modeling, several approaches to the problem of designing an injector to produce a 3-30 kA, 2-4 mm-diameter electron beam in the 10-20 MeV energy range were studied. The cathode may be small in diameter and immersed in a strong magnetic field, producing an equilibrium beam for transport to a target (the immersed case). This approach appears to be the most promising for applications such as radiography. The alternative is the conventional nonimmersed cathode. For the production of small-diameter electron beams in the range of 10-20 MeV, the authors propose an inductive-voltage-adder, single-(diode)-gap approach, e.g. SABRE instead of the conventional multigap linac. For the injector, they propose the use of a small-diameter cathode in a field of 40-60 kG. Calculations predict that very high current densities can be expected, with relative insensitivity to parameter variations.<>