Polarization control in high power microwaves from a rectangular cross section gyrotron

Summary form only given, as follows. We summarize the results of experiments on a gyrotron utilizing rectangular-cross-section (RCS) interaction cavities. Current issues under investigation include polarization control as a function of magnetic field, power versus pulselength of microwave emission, and mode competition. The electron beam driver producing an annular beam is the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V=-0.7 to -1.0 MV, I/sub diode/=1-10 kA, I/sub tube/=0.1-3 kA, and /spl tau//sub e-beam/=0.4-1.0 /spl mu/s. The annular e-beam is spun up into an axis-encircling beam by passing it through a magnetic cusp prior to entering the RCS interaction cavity. Initial experimental results show a high degree of polarization [P(TE/sub 10/)/P(TE/sub 01/)=30 or 1/30] as a function of cavity fields. Megawatt microwave output shifts from the fundamental mode, which dominates the next order mode by an order of magnitude, to the next order mode as the field is raised from 1.4 to 1.7 kGauss. Frequency measurements using microstrip bandpass filters and a superheterodyne mixer support this result as well as MAGIC simulations. MAGIC code simulations using various magnetic fields will be presented as well as results.