Electron beam quality in a cyclotron autoresonance accelerator

Abstract

An analysis of the electron beam dynamics in a cyclotron autoresonance accelerator (CARA) is presented. The beam is to be employed in harmonic convertor experiments to generate high-power centimeter-wavelength microwaves, with potential application as a driver for a next-generation electron-positron collider. The presentation will highlight the quality of the electron beam generated by this acceleration mechanism. For beam energies up to about 1 MeV and beam currents up to 50 A, the evolution of the axial velocity spread is determined by a self-consistent numerical solution of the governing nonlinear equations for an ensemble of electrons with finite initial emittance. It is shown that the requirement for an up-tapered guide magnetic field to maintain resonance leads to a diminution of the axial velocity (due to the mirror effect) that eventually causes the acceleration to cease. It is also shown that under some conditions a CARA can have an acceleration efficiency approaching 100%. An estimate is given, and examples are considered for the deterioration of a CARA beam's spatiotemporal character arising from self-fields.