A CHI wiggler ubitron amplifier experiment: wiggler characterization

Summary form only given. A 35 GHz CHI (Coaxial Hybrid Iron) wiggler ubitron amplifier experiment is under construction at the Naval Research Laboratory. The CHI wiggler configuration has the potential of generating high wiggler magnetic fields at short periods with excellent beam focusing and transport properties. This makes it a desirable configuration for the generation of high power coherent radiation in relatively compact systems. The CHI wiggler consists of alternating rings of magnetic and non-magnetic materials concentric with a central rod of similar alternating design but shifted along the axis by half a period. Once inserted in a solenoidal magnetic field, the CHI structure deforms the axial field to create a radial field oscillating with the same periodicity as the rings. An annular electron beam is propagated through the coaxial gap where the oscillating radial field imparts an azimuthal wiggle motion. The principal goals of the experiment are to investigate the performance tradeoffs involved in the CHI configuration for high frequency amplifiers operating at low voltages with small wiggler periods. The nominal design parameters are a center frequency of 35 GHz, wiggler period of 0.75 cm, and beam voltage of approximately 150 kV. A prototype CHI wiggler is presently being fabricated for use in conjunction with an existing 30 kG superconducting solenoid.