Multistage cyclotron autoresonance accelerator

Abstract

It has been shown previously that a cyclotron autoresonance accelerator (CARA) has a practical upper energy limit that arises from axial velocity stalling in the rising axial magnetic field. This paper shows that this upper energy limit can be overcome by operating a series of CARA stages, with each succeeding stage at a higher gyroharmonic. The accelerator would be driven from a single external rf source, and gyroharmonic operation in stages beyond the first would be accomplished by stagewise reduction in the guide magnetic field. Analytical and simulation results are presented to show, under ideal conditions, that stalling can thereby be avoided and acceleration to high energy can be achieved. For a three-stage CARA with a 15-A, 250-kV injected electron beam driven by 75 MW of rf power at 11.424 GHz, the results show that an energy of over 5 MeV can be reached at the end of the third stage, whereas a practical single-stage CARA with a 250-kV injected beam has an upper energy limit of about 1.7 MeV. It is also shown that tandem operation of a large number of CARA stages could, in principle, allow acceleration of electrons up to GeV energies.