Development of an X-band magnicon amplifier for the Next Linear Collider-cold cathode experiments and a thermionic design study

Summary form only given. The Naval Research Laboratory has been studying the operation of an 11 GHz frequency-doubling magnicon amplifier driven by a -650 kV, 225 A, 5.5-mm-diam. electron beam produced by a velvet cathode driven by a single-shot Marx generator. The magnicon circuit consists of a set of 5.56 GHz TM/sub 110/ deflection cavities (a drive cavity, two gain cavities, and a two-section /spl pi/-mode penultimate cavity) containing synchronously rotating modes that spin the beam up to high transverse momentum, followed by an 11.12 GHz TM/sub 210/ output cavity that uses a synchronously rotating mode to decelerate the electrons and generate microwave radiation. In the design, the electron spin-up develops progressively Through the deflection cavities. In the experiments, a plasma saturation effect was observed that limits the circulating power in each of the gain cavities to <10 kW. In order to overcome this low field saturation, the experiment was operated near the instability point of the penultimate cavity. We have designed a new thermionic magnicon experiment, incorporating an advanced high-convergence electron gun to produce a 500 kV, 200 A, 2-mm-diam. electron beam, an improved deflection cavity design, and an improved output cavity that employs side-coupling to extract the RF power through a pair of X-band waveguides separated by 135/spl deg/ around the azimuth of the cavity without destroying the symmetry of the rotating quadrupole mode. The predicted efficiency is /spl sim/60%.