Operation of a Ka-band CHI wiggler ubitron amplifier

Summary form only given, as follows. The status of a 35 GHz CHI (Coaxial Hybrid Iron) wiggler ubitron amplifier experiment being performed at the Naval Research Laboratory is presented. The purpose of the experiment is to study the CHI wiggler´s potential of generating high wiggler fields at short wiggler periods as well as its excellent beam focusing and transport properties. The wiggler is immersed in an applied axial field which acts to both create the wiggler field and enhance the interaction. This enhancement near autoresonance is also investigated, for both Group I and II orbits. The wiggler period is 6.4 mm. The operation point is chosen at grazing incidence (at 35 GHz) of beam and RF uncoupled dispersion curves, resulting in a wide instantaneous bandwidth. A SLAG klystron gun has been modified to produce an annular 100 kV, 10 A beam. Focusing of the beam from the gun into the CHI structure is provided by a system of three DC magnet coils. Broadband (/spl ap/20%) RF input and output couplers have been designed to couple from a rectangular TE/sub 10/ to the coaxial TE/sub 01/ interaction mode. Simulations using the above parameters have shown an intrinsic untapered efficiency of 6.75% when operating at an applied field of 7.7 kG. The instantaneous bandwidth was /spl ap/25%, with a gain of 28.3 dB, saturating at a distance of 63 cm for 100 W drive power. Results to date are reported, along with measurements of the performance of the separate components.