MULTISTAGE CYCLOTRON AUTORESONANCE ACCELERATOR

It has been shown previously that a cyclotron autoresonance accelerato r (CARA) has a practical upper energy limit that arises from axial vel ocity stalling in the rising axial magnetic field. This paper shows th at this upper energy limit can be overcome by operating a series of CA RA stages, with each succeeding stage at a higher gyroharmonic. The ac celerator would be driven from a single external rf source, and gyroha rmonic operation in stages beyond the first would be accomplished by s tagewise reduction in the guide magnetic field. Analytical and simulat ion results are presented to show, under ideal conditions, that stalli ng can thereby be avoided and acceleration to high energy can be achie ved. 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 e nergy of over 5 MeV can be reached at the end of the third stage, wher eas a practical single-stage CARA with a 250-kV injected beam has an u pper energy limit of about 1.7 MeV. It is also shown that tandem opera tion of a large number of CARA stages could, in principle, allow accel eration of electrons up to GeV energies.