A Variable Energy Racetrack Microtron

A racetrack microtron whose energy may be varied continuously from 4.5 to 18 MeV has been built at the University of Western Ontario, and has been operated to full energy. Electrons from an external electron gun are injected with an electrostatic inflector, and accelerated in a short sidecoupled linac section. The RF power delivered to the linac section can be varied by means of a power splitter, thus allowing the energy gain in the section to be adjusted continuously from 1.5 to 3 MeV. The accelerator can be operated in three different modes: single traversal of the linac section with a final beam energy of 1.5 to 3 MeV, n = 2 with three traversals of the linac covering the final energy range from 4.5 to 9 MeV and n = 1 with six traversals of the linac and a corresponding energy range of 9 to 18 MeV. The magnetic guide field consists of two 180° magnets with alternating high and low field regions. To satisfy the resonance conditions the average induction can be varied up to 0.6 T and the lengths of the drift space between the magnets can be adjusted by moving the pole pieces of the magnets.