First operation of a Ka-band CHI wiggler ubitron amplifier

Summary form only given. The 35 GHz center frequency CHI (Coaxial Hybrid Iron) niggler ubitron amplifier experiment being performed at the Naval Research Laboratory is presently in operation. The CHI wiggler is ideally suited for operation at short wiggler periods without sacrificing wiggler field magnitudes, leading to the possibility of lower voltage free-electron lasers. The wiggler period of the device under investigation is 6.4 mm, and the frequency band of operation is centered about 35 GHz. Due to the nature of the wiggler, which uses an applied axial field to create the wiggler field, there exists a gyroresonance effect between the wiggler motion and the cyclotron motion at a particular applied field. The possibility exists of using this axial field to enhance the interaction through the increased transverse motion of the beam. First results show amplification at both Group I and Group II regimes, i.e., below and above the gyroresonant field. Cyclotron resonance maser oscillation was also identified for certain applied field values on Group I orbits. These should not interfere with the interaction with the main TE01 coaxial mode. Efforts are currently under way to increase the gain and eliminate any interference due to the the cyclotron oscillation. Results to date will be presented.