The NRL Ka-band CHI wiggler ubitron amplifier

Summary form only given. A 35 GHz CHI (Coaxial Hybrid Ion) wiggler ubitron amplifier experiment is under construction at the Naval Research Laboratory. The purpose of the experiment is to study the CHI wiggler configuration´s potential of generating high wiggler magnetic fields at short periods with excellent beam focusing and transport properties. The nominal design parameters of the experiment are a center frequency of 35 GHz, wiggler period of 7.5 mm, and beam voltage of approximately 150 kV. Calculations have shown an intrinsic (untapered) efficiency of /spl ap/7% when operating at 6.3 kG axial field (wiggler field, B/sub w//spl ap/1270 G). The calculated gain was 36 dB, saturating at a distance of 46 cm. These parameters yield an instantaneous amplifier bandwidth of /spl ap/25%. There appears to be room for further improvement in efficiency, a matter that will be scrutinized more closely in the final design. Components of the experiment include a modified SLAC klystron electron gun (its beam converted from solid to annular), and the input and output RF couplers. Extensive work was performed on the design of the annular beam gun. This includes different techniques used in the development of the electron beam focusing coils, since the beam is immersed in a magnetic field from the cathode onward. In addition to the design of the components themselves, their placement in relation to each other in the gun-wiggler region is critical due to space limitation and beam transport issues. The techniques used for beam focusing were also used to study the transport of the beam from the gun output to the wiggler input.