High Power Fundamental Mode Large-orbit Gyrotron Experiment

A large-orbit gyrotron oscillator (LOG) is under development as a source of high power, 650 MHz radiation in the TE
^º
₁₁
mode. A stainless-steel cold cathode is used to produce a streaming relativistic (500 - 700 keV) annular electron beam. The E-layer begins rotating as it passes through a magnetic cusp and its energy is then extracted via the negative mass instability. We present experimental results from parameter surveys of beam energy, current, and magnetic field on the detected rf power levels. Initial experiments have demonstrated the generation of single-mode rf power in excess of 100 MW. Results from theoretical studies of this system, such as accessible cusp equilibria and cusp-limiting currents, start-oscillation current, and linear growth rates will be presented. Additionally, we present preliminary designs of a LOG consisting of a rectangular cross-section interaction region that excites the TE
^º
₁₀
mode.