Upper hybrid wave collective accelerator studies

The authors report progress in the development of a low-repetition-rate modulator for use in an upper-hybrid-wave collective accelerator project as well as initial results on wave excitation on a 400-kV, 150-400-A beam driven by a single-shot Marx-Blumlein pulser. Waves are excited as the beam propagates through a cavity where an interaction develops between the rotating beam and electromagnetic waves in the cavity. The cavity is tapered into a uniform guide in which all electromagnetic modes are cut off for the frequencies of interest while the cyclotron body wave on the beam continues to propagate. Measurements of the body wave downstream of the cavity are reported. It is pointed out that the accelerator concept is of interest for a variety of reasons, one of which is that it allows for the development of an accelerator in which the need for coupling circuits between the RF source and the accelerated beam is eliminated. A corollary of this is that the acceleration field is a maximum at the location of the beam being accelerated and not at the structure boundaries where breakdown may occur. A second important reason for the study is that the system is simple and eliminates the need for complex structures while retaining the essential features of an RF accelerator