HIGH-CURRENT RACETRACK MICROTRON AS A FREE-ELECTRON LASER DRIVER

A racetrack microtron combines the best features of a linac and a clas sical microtron. It might serve as a basis for free electron lasers to make these promising devices more compact and relatively cheap and th us available for many laboratories. At the same time it is known that stable acceleration in a racetrack is broken up at high intensity by a utomodulation of the beam current. It is shown in this paper that such modulation originates from positive feedback arising at some frequenc ies between the system rf cavity and the electron beam. The beam-cavit y interaction equations followed by a stability analysis are presented . A linear approximation is used to derive stability conditions, the l atter being represented in an analytical form followed by numerical ca lculations and a stability diagram. Comparing the results obtained wit h experimentally measured values shows the validity of the approach us ed. The physical meaning of observed intensity modulation as well as s ome measures of their suppression are discussed.